Iron is the intracellular metal involved in the production of DNA damage by oxygen radicals

Application of constant-current coulometry for estimation of plasma total antioxidant capacity and its relationship with transition metal contents

Simple and express coulometric method for the evaluation of the total antioxidant capacity (TAC) of human plasma based on the reaction with electrogenerated bromine is applied. TAC of plasma from patients with different ethiology of chronic renal failure was observed. The levels of antioxidant capacity for venous and arterial plasma are authentically different (15+/-1 kCl/L versus 11.7+/-0.7 kCl/L, p<0.01). The application of Vitamin E and ximedon as an antioxidant treatment significantly increase TAC level of plasma. Free liposoluble antioxidants in plasma in alpha-tocopherol units was determined. Redox potential of plasma is measured and its correlation with lg(TAC) is obtained. Transition metal contents of Fe, Cu, Mn, Ni, and Cr in plasma of patients with chronic renal failure is significantly higher than that for a control group. Correlation analysis has shown negative linear regression between TAC value and transition metals concentration in plasma. This confirms interrelation of processes with participation of free radicals, antioxidants and transition metals as donors of electrons in chain radical processes. Moreover, it shows utility of common parameters, TAC for example, for estimation of efficiency of antioxidant defense system in living organism, in particular its antioxidant status.

Stress responses in mycobacteria

Mycobacterium tuberculosis is a successful pathogen that overcomes numerous challenges presented by the immune system of the host. This bacterium usually establishes a chronic infection in the host where it may silently persist inside a granuloma until, a failure in host defenses, leads to manifestation of the disease. None of the conventional anti-tuberculosis drugs are able to target these persisting bacilli. Development of drugs against such persisting bacilli is a constant challenge since the physiology of these dormant bacteria is still not understood at the molecular level. Some evidence suggests that the in vivo environment encountered by the persisting bacteria is anoxic and nutritionally starved. Based on these assumptions, anaerobic and starved cultures are used as models to study the molecular basis of dormancy. This review outlines the problem of persistence of M. tuberculosis and the various in vitro models used to study mycobacterial latency. The basis of selecting the nutritional starvation model has been outlined here. Also, the choice of M. smegmatis as a model suitable for studying mycobacterial latency is discussed. Lastly, general issues related to oxidative stress and bacterial responses to it have been elaborated. We have also discussed general control of OxyR-mediated regulation and emphasized the processes which manifest in the absence of functional OxyR in the bacteria. Lastly, a new class of protein called Dps has been reviewed for its important role in protecting DNA under stress.

“In vitro” protection of DNA from Fenton reaction by plant polyphenol verbascoside

The protection effect of verbascoside (Ver) against Fenton reaction on plasmid pBR322 DNA was studied using agarose gel electrophoresis and UV-visible spectroscopy. The pBR322 plasmid DNA is damaged by hydroxyl radical (OH*) generated from the Fenton reaction with H2O2 and Fe(II) or Fe(III). This DNA damage is characterized by the diminution of supercoiled DNA forms or by the increase of relaxed or linear DNA forms after oxidative attack. The UV spectrum study showed that verbascoside can form complexes with Fe(II) or Fe(III), and the complexation can be reversed by the addition of EDTA. The formation constants of verbascoside-Fe complexes were estimated as 10(21.03) and 10(31.94) M(-2) for Fe(II) and Fe(III) respectively. The inhibition of Fenton reaction by verbascoside could be partially explained by the sequestration of Fe ions.

Hsp27 consolidates intracellular redox homeostasis by upholding glutathione in its reduced form and by decreasing iron intracellular levels

Small stress proteins [small heat shock proteins (sHsps)] are molecular chaperones that modulate the ability of cells to respond to oxidative stress. The current knowledge concerning the protective mechanism generated by the expression of mammalian heat shock protein-27 (Hsp27) that allows cells to increase their resistance to oxidative stress is presented. We describe the effects mediated by Hsp27 expression toward crucial enzymes such as glucose-6-phosphate dehydrogenase and glutathione reductase that uphold glutathione in its reduced form. New data are presented showing that the expression of sHsps correlates with a drastic decrease in the intracellular level of iron, a catalyzer of hydroxyl radical (OH( . )) generation. A decreased ability of sHsps expressing cells to concentrate iron will therefore end up in a decreased level of oxidized proteins. In addition, we propose a role of Hsp27 in the presentation of oxidized proteins to the proteasome degradation machinery. We also present an analysis of several Hsp27 mutants that suggests that the C-terminal part of this stress protein is essential for its protective activity against oxidative stress.

Genotoxic consequences associated with oxidative damage in testis of mice subjected to iron intoxication

While iron-induced testicular dysfunction has been demonstrated adequately, the mechanism(s) involved and the genotoxic implications are not fully understood. In order to understand the genotoxic effects of iron intoxication, initially induction of oxidative stress response in testis of adult albino mice (CFT-Swiss) was ascertained following administration (i.p.) of acute sub-lethal doses of iron dextran (ID). Subsequently, multiple sub-lethal doses (50, 100 and 200 mg/kg bw/day) were employed to characterize effects on lipid peroxidation (LPO) in testis (homogenates, microsomal/mitochondrial fractions), DNA damage and incidence of abnormal sperms. While acute doses of ID induced only a marginal increase in LPO response in testis at 24 h of administration, multiple doses elicited a moderate (30-40%) increase in LPO in whole homogenates and significant dose-related elevation in both mitochondrial (20-45%) and microsomal fractions (25-65%). This was associated with significant increase in DNA damage in the testis as evidenced by increased single strand breaks in a fluorimetric analysis of DNA unwinding (FADU) assay. Further, evidences of oxidative damage in testis was evident in terms of increased protein carbonyls and altered antioxidant enzymic activities. The genotoxic implications were investigated by quantification of the frequency of abnormal sperms sampled at specific periods during spermatogenetic cycle. Nearly three- to seven-fold increase in percent abnormal sperms among the ID treated males were evident during the first 3 weeks although the counts were unaffected. Interestingly, in a classical dominant lethal (DL) assay, mating of ID treated (100 mg/kg bw/day for 5 days) males sequentially for a period of 5 weeks with untreated females resulted in a significant increase in male-mediated dominant lethal type mutations (the frequency of dead implants) during the first 3 weeks only indicating a stage-specific effect on post-meiotic germ cells. These findings provide an account of the early oxidative damage in testis in vivo following exposure to low levels of iron which may be wholly or in part responsible for the genotoxic consequences observed in this model of iron overload.

Oxidised guanidinohydantoin (Ghox) and spiroiminodihydantoin (Sp) are major products of iron- and copper-mediated 8-oxo-7,8-dihydroguanine and 8-oxo-7,8-dihydro-2′-deoxyguanosine oxidation

8-Oxo-7,8-dihydroguanine (8-oxoGua), an important biomarker of DNA damage in oxidatively generated stress, is highly reactive towards further oxidation. Much work has been carried out to investigate the oxidation products of 8-oxoGua by one-electron oxidants, singlet oxygen, and peroxynitrite. This report details for the first time, the iron- and copper-mediated Fenton oxidation of 8-oxoGua and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo). Oxidised guanidinohydantoin (Gh(ox)) was detected as the major product of oxidation of 8-oxoGua with iron or copper and hydrogen peroxide, both at pH 7 and pH 11. Oxaluric acid was identified as a final product of 8-oxoGua oxidation. 8-oxodGuo was subjected to oxidation under the same conditions as 8-oxoGua. However, dGh(ox) was not generated. Instead, spiroiminodihydantoin (Sp) was detected as the major product for both iron and copper mediated oxidation at pH 7. It was proposed that the oxidation of 8-oxoGua was initiated by its one-electron oxidation by the metal species, which leads to the reactive intermediate 8-oxoGua (+), which readily undergoes further oxidation. The product of 8-oxoGua and 8-oxodGuo oxidation was determined by the 2'-deoxyribose moiety of the 8-oxodGuo, not whether copper or iron was the metal involved in the oxidation.

Nuclear ferritin in corneal epithelial cells: tissue-specific nuclear transport and protection from UV-damage

We have identified the heavy chain of ferritin as a developmentally regulated nuclear protein of embryonic chicken corneal epithelial cells. The nuclear ferritin is assembled into a supramolecular form that is indistinguishable from the cytoplasmic form of ferritin found in other cell types. Thus it most likely has iron-sequestering capabilities. Free iron, via the Fenton reaction, is known to exacerbate UV-induced and other oxidative damage to cellular components, including DNA. Since corneal epithelial cells are constantly exposed to UV light, we hypothesized that the nuclear ferritin might protect the DNA of these cells from free radical damage. To test this possibility, primary cultures of cells from corneal epithelium and other tissues were UV irradiated, and damage to DNA was detected by an in situ 3'-end labeling assay. Consistent with the hypothesis, corneal epithelial cells with nuclear ferritin had significantly less DNA breakage than the other cells types examined. However, when the expression of nuclear ferritin was inhibited the cells now became much more susceptible to UV-induced DNA damage. Since ferritin is normally cytoplasmic, corneal epithelial cells must have a mechanism that effects its nuclear localization. We have determined that this involves a nuclear transport molecule which binds to ferritin and carries it into the nucleus. This transporter, which we have termed ferritoid for its similarity to ferritin, has at least two domains. One domain is ferritin-like and is responsible for binding the ferritin; the other domain contains a nuclear localization signal that is responsible for effecting the nuclear transport. Therefore, it seems that corneal epithelial cells have evolved a novel, nuclear ferritin-based mechanism for protecting their DNA against UV damage. In addition, since ferritoid is structurally similar to ferritin, it may represent an example of a nuclear transporter that evolved from the molecule it transports (i.e., ferritin).

Hyperinsulinemia may boost both hematocrit and iron absorption by up-regulating activity of hypoxia-inducible factor-1α

There is growing evidence that increases in both hematocrit and body iron stores are components of the insulin resistance syndrome. The ability of insulin and of IGF-I - whose effective activity is increased in the context of insulin resistance - to boost activity of the transcription factor hypoxia-inducible factor-1alpha (HIF-1alpha), may be at least partially responsible for this association. HIF-1alpha, which functions physiologically as a detector of both hypoxia and iron-deficiency, promotes synthesis of erythropoietin, and may also mediate the up-regulatory impact of hypoxia on intestinal iron absorption. Insulin/IGF-I may also influence erythropoiesis more directly, as they are growth factors for developing reticulocytes. Conversely, the activation of HIF-1alpha associated with iron deficiency may be responsible for the increased glucose tolerance noted in iron-deficient animals; HIF-1alpha promotes efficient glucose uptake and glycolysis - a sensible adaptation to hypoxia - by inducing increased synthesis of glucose transporters and glycolytic enzymes. Recent reports that phlebotomy can increase the efficiency of muscle glucose uptake in lean healthy omnivores are intriguing and require further confirmation. Whether increased iron stores contribute to the elevated vascular risk associated with insulin resistance is doubtful, inasmuch as most prospective studies fail to correlate serum ferritin or transferrin saturation with subsequent vascular events. However, current data are reasonably consistent with the possibility that moderately elevated iron stores are associated with increased overall risk for cancer - and for colorectal cancer in particular; free iron may play a catalytic role in 'spontaneous' mutagenesis. Thus, iron excess may mediate at least some of the increased cancer risk associated with insulin resistance and heme-rich diets. People who are insulin resistant can minimize any health risk associated with iron overload by avoiding heme-rich flesh foods and donating blood regularly.

Ferritoid, a tissue-specific nuclear transport protein for ferritin in corneal epithelial cells

Previously we reported that ferritin in corneal epithelial (CE) cells is a nuclear protein that protects DNA from UV damage. Since ferritin is normally cytoplasmic, in CE cells, a mechanism must exist that effects its nuclear localization. We have now determined that this involves a nuclear transport molecule we have termed ferritoid. Ferritoid is specific for CE cells and is developmentally regulated. Structurally, ferritoid contains multiple domains, including a functional SV40-type nuclear localization signal and a ferritin-like region of approximately 50% similarity to ferritin itself. This latter domain is likely responsible for the interaction between ferritoid and ferritin detected by co-immunoprecipitation analysis. To test functionally whether ferritoid is capable of transporting ferritin into the nucleus, we performed cotransfections of COS-1 cells with constructs for ferritoid and ferritin. Consistent with the proposed nuclear transport function for ferritoid, co-transfections with full-length constructs for ferritoid and ferritin resulted in a preferential nuclear localization of both molecules; this was not observed when the nuclear localization signal of ferritoid was deleted. Moreover, since ferritoid is structurally similar to ferritin, it may be an example of a nuclear transporter that evolved from the molecule it transports (ferritin).

Redox-sensitive mechanisms of phytochemical-mediated inhibition of cancer cell proliferation (review)

Phytochemicals are potential cancer chemopreventive agents, based partly on cellular research establishing that phytochemicals inhibit the proliferation of cancer cells. To elucidate the mechanism of phytochemicals, a basic understanding is needed of what stimulates cancer cell proliferation. Cancer cells, particularly those that are highly invasive or metastatic, may require a certain level of oxidative stress to maintain a balance between undergoing either proliferation or apoptosis. They constitutively generate large but tolerable amounts of H2O2 that apparently function as signaling molecules in the mitogen-activated protein kinase pathway to constantly activate redox-sensitive transcription factors and responsive genes that are involved in the survival of cancer cells as well as their proliferation. With such a reliance of cancer cells on H2O2 it follows that if the excess H2O2 can be scavenged by phenolic phytochemicals having antioxidant activity, the oxidative stress-responsive genes can be suppressed and consequently cancer cell proliferation inhibited. On the other hand, phenolic phytochemicals and another group of phytochemicals known as isothiocyanates can induce the formation of H2O2 to achieve an intolerable level of high oxidative stress in cancer cells. As an early response, the stress genes are activated. However, when the critical threshold for cancer cells to cope with the induced oxidative stress has been reached, key cellular components such as DNA are damaged irreparably. In conjunction, genes involved in initiating cell cycle arrest and/or apoptosis are activated. Therefore, phytochemicals can either scavenge the constitutive H2O2 or paradoxically generate additional amounts of H2O2 to inhibit the proliferation of cancer cells.

Protection of human lung cells against hyperoxia using the DNA base excision repair genes hOgg1 and Fpg

Hyperoxia causes pulmonary toxicity in part by injuring alveolar epithelial cells. Previous studies have shown that toxic oxygen-derived species damage DNA and this damage is recognized and repaired by either human enzyme 8-oxoguanine DNA glycosylase (hOgg1) or Escherichia coli enzyme formamidopyrimidine DNA glycosylase (Fpg). To determine whether these DNA repair proteins can reduce O(2)-mediated DNA damage in lung cells, A549 lung epithelial cells were transduced with either hOgg1 or Fpg using a retroviral vector containing enhanced green fluorescent protein. Expression of each gene in the transduced cells was confirmed by fluorescent microscopy, Northern blotting, Western blotting, and an enzymatic oligonucleotide cleavage assay. A549 cells expressing either hOgg1 or Fpg were protected from hyperoxia as evidenced by a decrease in DNA damage and a corresponding increase in cell survival. Further, we determined that overexpression of hOgg1 or Fpg partially mitigated the toxic effects of hydrogen peroxide in lung cells. Our data suggest that increased expression of DNA base excision repair genes might represent a new approach for protecting critical lung cells from the toxic effects of hyperoxia.

Identification of Rhus verniciflua Stokes compounds that exhibit free radical scavenging and anti-apoptotic properties

Rhus verniciflua Stokes (RVS) is a widely used herbal plant with various biological properties. Our previous study using cultured neuronal cells showed that an ethanol extract of RVS had strong antioxidant properties. In this study, we characterized the antioxidant activity of the RVS ethanol extract and identified the active compounds responsible for this activity. From the RVS ethanol extract, we derived three water-eluted fractions and another three fractions eluted by organic solvents, and determined that the water-eluted fractions are what protect against reactive oxygen species (ROS) generated by iron and enzymes. Water-eluted fraction F(2) was the most efficient antioxidant. Moreover, DNA fragmentation and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) staining experiments revealed that F(2) also protects against thymocyte apoptosis mediated by hydroxyl radicals. Finally, EI-MS, (1)H-NMR, and (13)C-NMR spectra signals confirmed that the fraction contained flavonoid derivatives, including fustin, quercetin, butein, and sulfuretin. These results suggest that the flavonoid derivatives in F(2) are the compounds in the RVS ethanol extract that act as antioxidants.

The radiation-induced lesions which trigger the bystander effect

The ionizing radiation induced bystander effect is initiated by damage to a cellular molecule which then gives rise to a signal exported to other cells. The nature of this damage is considered with the understanding that it may not be the same as that responsible for the traditional cellular effects of radiation. Consideration is give to amounts of endogenous damage and to radiation yields of the various candidate lesions.

Hepatothermic therapy of obesity: rationale and an inventory of resources

Hepatothermic therapy (HT) of obesity is rooted in the observation that the liver has substantial capacities for both fatty acid oxidation and for thermogenesis. When hepatic fatty acid oxidation is optimized, the newly available free energy may be able to drive hepatic thermogenesis, such that respiratory quotient declines while basal metabolic rate increases, a circumstance evidently favorable for fat loss. Effective implementation of HT may require activation of carnitine palmitoyl transferase-1 (rate-limiting for fatty acid beta-oxidation), an increase in mitochondrial oxaloacetate production (required for optimal Krebs cycle activity), and up-regulation of hepatic thermogenic pathways. The possible utility of various natural agents and drugs for achieving these objectives is discussed. Potential components of HT regimens include EPA-rich fish oil, sesamin, hydroxycitrate, pantethine, L-carnitine, pyruvate, aspartate, chromium, coenzyme Q10, green tea polyphenols, conjugated linoleic acids, DHEA derivatives, cilostazol, diazoxide, and fibrate drugs. Aerobic exercise training and very-low-fat, low-glycemic-index, high-protein or vegan food choices may help to establish the hormonal environment conducive to effective HT. High-dose biotin and/or metformin may help to prevent an excessive increase in hepatic glucose output. Since many of the agents contemplated as components of HT regimens are nutritional or food-derived compounds likely to be health protective, HT is envisioned as an on-going lifestyle rather than as a temporary 'quick fix'. Initial clinical efforts to evaluate the potential of HT are now in progress.

Iron and its sensitive balance in the cell

Iron is vital in life because it is an important component of molecules that undergoes redox reactions or transport oxygen. However, the existence of two stable and inter-convertible forms of iron, iron(III) and iron(II), makes possible one electron being transferred to or captured from other species to form radicals. In particular, superoxide and hydroxyl radicals may be formed in these reactions, both with capacity of attacking other molecules. DNA is one important target and a vast literature exists showing that attack of hydroxyl radical to DNA leads to cell death cellular necrosis, apoptosis, mutation and malignant transformation. Therefore, a fine balance must exist at various levels of an organism to maintain iron concentration in a narrow range, above and below which deleterious effects of distinct nature occur. This review will deal with the formation of oxygen reactive species in iron participating reactions, defenses in the organism against these species, the different mechanisms of iron homeostasis and iron deficiency and iron overload related diseases.

Mechanism of guanine-specific DNA damage by oxidative stress and its role in carcinogenesis and aging

Reactive species generated by chemicals and UV radiation can cause sequence-specific DNA damage and play important roles in mutagenesis, carcinogenesis and aging. We have investigated sequence specificity of oxidative stress-mediated DNA damage by using 32P-labeled DNA fragments obtained from the human c-Ha-ras-1 and p53 genes. Free hydroxyl radical causes DNA damage with no marked site specificity. Reactive nitrogen species, sulfate radicals, nitrogen-centered radicals, benzoyloxyl radical and alkoxyl radical show different sequence specificity. Benzoyloxyl radical specifically causes damage to the 5'-G in GG sequence. UVA radiation also causes DNA damage at this site through electron transfer in the presence of certain photosensitizers. The 5'-G in GG sequence is easily oxidized because a large part of the highest occupied molecular orbital is distributed on this site. On the basis of these findings, the sequence specificity of DNA damage is presumably determined by (a) redox potential of reactive species; (b) ionization potential of DNA bases; and (c) site-specific binding of metal ion to DNA. Here we discuss the mechanisms of sequence-specific DNA damage in relation to carcinogenesis and aging.

Cellular sites of H2O2-induced damage and their protection by nitroxides

While the exact mechanism of H2O2-induced cytotoxicity is unknown, there is considerable evidence implicating DNA as a primary target. A recent study showed that a cell-impermeable nitroxide protected mammalian cells from H2O2-induced cell killing and suggested that the protection was mediated through cell membrane-bound or extracellular factors. To further define the protective properties of nitroxides, Chinese hamster V79 cells were exposed to H2O2 with or without cell-permeable and impermeable nitroxides and selected metal chelators. EPR spectroscopy and paramagnetic line broadening agents were used to distinguish between intra- and extracellular nitroxide distribution. To study the effectiveness of nitroxide protection, in the absence of a cell membrane, H2O2-mediated damage to supercoiled plasmid DNA was evaluated. Both deferrioxamine and Tempol cross the cell membrane, and inhibited H2O2-mediated cell killing, whereas the cell-impermeable DTPA and nitroxide, CAT-1, failed to protect. Similar protective effects of the chelators and nitroxides were observed when L-histidine, which enhances intracellular injury, was added to H2O2. In contrast, when damage to plasmid DNA was induced (in the absence of a cell membrane), both nitroxides were protective. Collectively, these results do not support a role for membrane-bound or extracellular factors in mediating H2O2 cytotoxicity in mammalian cells.

Current prospects for controlling cancer growth with non-cytotoxic agents--nutrients, phytochemicals, herbal extracts, and available drugs

In animal or cell culture studies, the growth and spread of cancer can be slowed by many nutrients, food factors, herbal extracts, and well-tolerated, available drugs that are still rarely used in the clinical management of cancer, in part because they seem unlikely to constitute definitive therapies in themselves. However, it is reasonable to expect that mechanistically complementary combinations of these measures could have a worthwhile impact on survival times and, when used as adjuvants, could improve the cure rates achievable with standard therapies. The therapeutic options available in this regard include measures that: down-regulate serum free IGF-I; suppress the synthesis of mevalonic acid and/or certain derivatives thereof; modulate arachidonate metabolism by inhibiting 5-lipoxygenase, 12-lipoxygenase, or COX-2; antagonize the activation of AP-1 transcription factors; promote the activation of PPAR-gamma transcription factors; and that suppress angiogenesis by additional mechanisms. Many of these measures appear suitable for use in cancer prevention.

Retinol supplementation induces DNA damage and modulates iron turnover in rat Sertoli cells

Recent intervention studies revealed that supplementation with retinoids resulted in a higher incidence of lung cancer. Recently the causal mechanism has begun to be clarified. We report here that retinol caused cellular DNA damage probably involving cellular iron accumulation. Retinol (7 microM) significantly induced DNA single strands breaks, DNA fragmentation and production of 8-oxo-7, 8-dihydro-2'-deoxyguanosine in cultured Sertoli cells. In contrast, lower doses seemed not to induce single-strands break in this experimental model. The breaks in DNA were inhibited by an iron scavenger; and 7 microM retinol treatment modulated iron turnover leading to iron accumulation, suggesting that iron ions were required for the retinol cellular effects. These findings suggest that retinol-induced DNA damage was associated with the modulation of iron turnover, and these characteristics could be responsible for the increased incidence of lung cancer associated with retinoids supplementation.

The iron chelator pyridoxal isonicotinoyl hydrazone (PIH) and its analogues prevent damage to 2-deoxyribose mediated by ferric iron plus ascorbate

Iron chelating agents are essential for treating iron overload in diseases such as beta-thalassemia and are potentially useful for therapy in non-iron overload conditions, including free radical mediated tissue injury. Deferoxamine (DFO), the only drug available for iron chelation therapy, has a number of disadvantages (e.g., lack of intestinal absorption and high cost). The tridentate chelator pyridoxal isonicotinoyl hydrazone (PIH) has high iron chelation efficacy in vitro and in vivo with high selectivity and affinity for iron. It is relatively non-toxic, economical to synthesize and orally effective. We previously demonstrated that submillimolar levels of PIH and some of its analogues inhibit lipid peroxidation, ascorbate oxidation, 2-deoxyribose degradation, plasmid DNA strand breaks and 5,5-dimethylpyrroline-N-oxide (DMPO) hydroxylation mediated by either Fe(II) plus H(2)O(2) or Fe(III)-EDTA plus ascorbate. To further characterize the mechanism of PIH action, we studied the effects of PIH and some of its analogues on the degradation of 2-deoxyribose induced by Fe(III)-EDTA plus ascorbate. Compared with hydroxyl radical scavengers (DMSO, salicylate and mannitol), PIH was about two orders of magnitude more active in protecting 2-deoxyribose from degradation, which was comparable with some of its analogues and DFO. Competition experiments using two different concentrations of 2-deoxyribose (15 vs. 1.5 mM) revealed that hydroxyl radical scavengers (at 20 or 60 mM) were significantly less effective in preventing degradation of 2-deoxyribose at 15 mM than 2-deoxyribose at 1.5 mM. In contrast, 400 microM PIH was equally effective in preventing degradation of both 15 mM and 1.5 mM 2-deoxyribose. At a fixed Fe(III) concentration, increasing the concentration of ligands (either EDTA or NTA) caused a significant reduction in the protective effect of PIH towards 2-deoxyribose degradation. We also observed that PIH and DFO prevent 2-deoxyribose degradation induced by hypoxanthine, xanthine oxidase and Fe(III)-EDTA. The efficacy of PIH or DFO was inversely related to the EDTA concentration. Taken together, these results indicate that PIH (and its analogues) works by a mechanism different than the hydroxyl radical scavengers. It is likely that PIH removes Fe(III) from the chelates (either Fe(III)-EDTA or Fe(III)-NTA) and forms a Fe(III)-PIH(2) complex that does not catalyze oxyradical formation.

Mitochondrial aconitase is a source of hydroxyl radical. An electron spin resonance investigation

Mitochondrial aconitase (m-aconitase) contains a [4Fe-4S](2+) cluster in its active site that catalyzes the stereospecific dehydration-rehydration of citrate to isocitrate in the Krebs cycle. It has been proposed that the [4Fe-4S](2+) aconitase is oxidized by superoxide, generating the inactive [3Fe-4S](1+) aconitase. In this reaction, the likely products are iron(II) and hydrogen peroxide. Consequently, the inactivation of m-aconitase by superoxide may increase the formation of hydroxyl radical ((*)OH) through the Fenton reaction in mitochondria. In this work, evidence for the generation of (*)OH from the reaction of m-aconitase with superoxide is provided using ESR spin trapping experiments with 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide and alpha-phenyl-N-tert-butylnitrone. Formation of free ( small middle dot)OH was verified with the (*)OH scavenger Me(2)SO, which forms methyl radical upon reacting with (*)OH. The addition of Me(2)SO to incubation mixtures containing m-aconitase and xanthine/xanthine oxidase yielded methyl radical, which was detected by ESR spin trapping. Methyl radical formation was further confirmed using [(13)C]Me(2)SO. Parallel low temperature ESR experiments demonstrated that the generation of the [3Fe-4S](1+) cluster increased with increasing additions of superoxide to m-aconitase. This reaction was reversible, as >90% of the initial aconitase activity was recovered upon treatment with glutathione and iron(II). This mechanism presents a scenario in which (*)OH may be continuously generated in the mitochondria.

Retinol-induced elevation of ornithine decarboxylase activity in cultured rat Sertoli cells is attenuated by free radical scavenger and by iron chelator

We investigated retinol effects in ornithine decarboxylase activity in Sertoli cells. We also tested the hypothesis that free radical scavengers and iron chelators may attenuate the effect of retinol. Sertoli cells isolated from 15-day-old Wistar rats were previously cultured for 48 h and then treated with retinol by 24 h with or without mannitol (1 mM) or 1,10 phenanthroline (100 microM). We measured ornithine decarboxylase and catalase activities and malondialdehyde concentrations in response to retinol treatment. In response to 7 microM retinol treatment ornithine decarboxylase activity increased 30%. Retinol-induced ornithine decarboxylase activity was significantly decreased by addition of free radical scavenger (mannitol) or iron chelator (1,10 phenanthroline). In addition the same effect was observed in catalase increased activity and in malondialdehyde concentrations. These results suggest that retinol treatment induced ornithine decarboxylase and catalase activity and increased malondialdehyde concentration. These effects appear to be mediate by ROS.

Determination of rate constants for the reaction of hydroxyl radicals with some purines and pyrimidines using sunlight

Sunlight mediated hydroxyl radical production from aqueous ferric perchlorate at low pH has been investigated using deoxyribose-thiobarbituric acid assay. The rate of production of hydroxyl radical was found to be dependent on the time of irradiation. Hydroxyl radical scavengers can compete with deoxyribose for hydroxyl radicals produced in the system leading to a decreased yield of thiobarbituric acid chromogen. The second-order rate constants of the added scavengers can be determined using a simple competition kinetic method. The rate constants for the reaction of hydroxyl radical with a number of purine and pyrimidine derivatives were determined using this method. The rate constants obtained (1-7 x 10(9) dm(3) mol(-1) s(-1)) were found to be in good agreement with those reported using pulse radiolysis technique. The rate constants of dimethyluracil, xanthosine, amino and methyl substituted pyrimidines, cytidine monophosphate and uridine monophosphate were also determined by this method. It is proposed that sunlight mediated production of hydroxyl radical coupled with deoxyribose-thiobarbituric acid assay is a simple and efficient method for the determination of rate constants for the reaction of hydroxyl radical with a wide range of biomolecules.

Apoptosis in Ca2 + reperfusion injury of cultured astrocytes: roles of reactive oxygen species and NF-kappaB activation

We previously reported that incubation of cultured astrocytes in Ca2 + -containing medium after exposure to Ca2 + -free medium caused Ca2 + influx followed by delayed cell death. Here, we studied the mechanisms underlying the Ca2 + -mediated injury of cultured astrocytes. Our results show that Ca2 + reperfusion injury of astrocytes appears to be mediated by apoptosis, as demonstrated by DNA fragmentation and prevention of death by caspase-3 inhibitors. Paradoxical Ca2 + challenge stimulated rapidly reactive oxygen species (ROS) production. Ca2 + reperfusion injury of astrocytes was influenced by several reagents which modified ROS production. When astrocytes were exposed to hydrogen peroxide (H2O2) for 30 min and then incubated without H2O2 for 1-5 days, cell toxicity including apoptosis was observed. Ca2 + reperfusion injury induced by Ca2 + depletion or H2O2 exposure was blocked by the iron chelator 1, 10-phenanthroline, the NF-kappaB inhibitor pyrrolidinedithiocarbamate and the calcineurin inhibitor FK506. Incubation in normal medium after H2O2 exposure rapidly increased the level of nuclear NF-kappaB p65 subunit, and the effect was blocked by 1,10-phenanthroline, pyrrolidinedithiocarbamate and FK506. These findings indicate that Ca2 + reperfusion-induced apoptosis is mediated at least partly by ROS production and ROS cause NF-kappaB activation in cultured astrocytes.

Polyphenol tannic acid inhibits hydroxyl radical formation from Fenton reaction by complexing ferrous ions

Tannic acid (TA), a plant polyphenol, has been described as having antimutagenic, anticarcinogenic and antioxidant activities. Since it is a potent chelator of iron ions, we decided to examine if the antioxidant activity of TA is related to its ability to chelate iron ions. The degradation of 2-deoxyribose induced by 6 microM Fe(II) plus 100 microM H2O2 was inhibited by TA, with an I50 value of 13 microM. Tannic acid was over three orders of magnitude more efficient in protecting against 2-deoxyribose degradation than classical *OH scavengers. The antioxidant potency of TA was inversely proportional to Fe(II) concentration, demonstrating a competition between H2O2 and AT for reaction with Fe(II). On the other hand, the efficiency of TA was nearly unchanged with increasing concentrations of the *OH detector molecule, 2-deoxyribose. These results indicate that the antioxidant activity of TA is mainly due to iron chelation rather than *OH scavenging. TA also inhibited 2-deoxyribose degradation mediated by Fe(III)-EDTA (iron = 50 microM) plus ascorbate. The protective action of TA was significantly higher with 50 microM EDTA than with 500 microM EDTA, suggesting that TA removes Fe(III) from EDTA and forms a complex with iron that cannot induce *OH formation. We also provided evidence that TA forms a stable complex with Fe(II), since excess ferrozine (14 mM) recovered 95-96% of the Fe(II) from 10 microM TA even after a 30-min exposure to 100-500 microM H2O2. Addition of Fe(III) to samples containing TA caused the formation of Fe(II)n-TA, complexes, as determined by ferrozine assays, indicating that TA is also capable of reducing Fe(III) ions. We propose that when Fe(II) is complexed to TA, it is unable to participate in Fenton reactions and mediate *OH formation. The antimutagenic and anticarcinogenic activity of TA, described elsewhere, may be explained (at least in part) by its capacity to prevent Fenton reactions.

Chelating of iron and copper alters properties of DNA in L5178Y cells, as revealed by the comet assay

We have previously found different proportions of iron and copper in nuclei of two sublines of murine lymphoma L5178Y (LY) and proposed a model of chromatin organization with these metal ions at the DNA attachment sites. We now examine the effect of chelators, desferal (DFO, iron-specific) and neocupreine (NEO, copper-specific) on DNA of LY-R and LY-S cells, using the comet and micronuclei frequency tests. There is less copper and more iron in LY-R nuclei than in LY-S nuclei. Accordingly, the effect of NEO is more marked in LY-R than in LY-S cells and in both sublines it is expressed as enhanced tail moment (measure of DNA damage in the comet assay) and increased micronuclei frequency. On the contrary, the effect of DFO on the tail moment is less pronounced in LY-R than in LY-S cells. With increasing DFO concentrations, there is a gradual decrease in the tail moment values below the control level in LY-S cells. In LY-R cells the tail moment values initially increase, then gradually decrease, eventually falling below the control level. This points to a dramatic conformational change that masks the effect of DNA discontinuities. The presence of the latter is indicated by the increase in micronuclei frequency. These results support the postulated differential role of iron and copper ions in maintaining the higher order DNA structure in LY sublines.

Characterisation of Fasciola hepatica cytochrome c peroxidase as an enzyme with potential antioxidant activity in vitro

Cytochrome c peroxidase oxidises hydrogen peroxide using cytochrome c as the electron donor. This enzyme is found in yeast and bacteria and has been also described in the trematodes Fasciola hepatica and Schistosoma mansoni. Using partially purified cytochrome c peroxidase samples from Fasciola hepatica we evaluated its role as an antioxidant enzyme via the investigation of its ability to protect against oxidative damage to deoxyribose in vitro. A system containing FeIII-EDTA plus ascorbate was used to generate reactive oxygen species superoxide radical, H2O2 as well as the hydroxyl radical. Fasciola hepatica cytochrome c peroxidase effectively protected deoxyribose against oxidative damage in the presence of its substrate cytochrome c. This protection was proportional to the amount of enzyme added and occurred only in the presence of cytochrome c. Due to the low specific activity of the final partially purified sample the effects of ascorbate and calcium chloride on cytochrome c peroxidase were investigated. The activity of the partially purified enzyme was found to increase between 10 and 37% upon reduction with ascorbate. However, incubation of the partially purified enzyme with 1 mM calcium chloride did not have any effect on enzyme activity. Our results showed that Fasciola hepatica CcP can protect deoxyribose from oxidative damage in vitro by blocking the formation of the highly toxic hydroxyl radical (.OH). We suggest that the capacity of CcP to inhibit .OH-formation, by efficiently removing H2O2 from the in vitro oxidative system, may extend the biological role of CcP in response to oxidative stress in Fasciola hepatica.

Synergistic lethal effect between hydrogen peroxide and neocuproine (2,9-dimethyl 1,10-phenanthroline) in Escherichia coli

Despite 2,9-dimethyl 1,10-phenanthroline (NC) has been extensively used as a potential inhibitor of damage due to oxidative stress in biological systems, the incubation of E. coli cultures with the copper ion chelator NC prior to the challenge with hydrogen peroxide caused a lethal synergistic effect. The SOS response seems to be involved in the repair of the synergistic lesions through the recombination pathway. Furthermore, there is evidence for the UvrABC excinuclease participation in the repair of the synergistic lesions, and the base excision repair may also be required for bacterial survival to the synergistic effect mainly at high concentrations of H2O2, being the action of Fpg protein an important event. Incubation of lexA (Ind-) cultures with iron (II) ion chelator 2,2'-dipyridyl simultaneously with NC prevented the lethal synergistic effect. This result suggests an important role of the Fenton reaction on the phenomenon. NC treatment was able to increase the number of DNA strand breaks (DNAsb) induced by 10 mM of H2O2 in lexA (Ind-) strain and the simultaneous treatment with 2,2'-dipyridyl was able to block this effect.

Sequence-specific DNA cleavage by Fe2+-mediated fenton reactions has possible biological implications

Preferential cleavage sites have been determined for Fe2+/H2O2-mediated oxidations of DNA. In 50 mM H2O2, preferential cleavages occurred at the nucleoside 5' to each of the dG moieties in the sequence RGGG, a sequence found in a majority of telomere repeats. Within a plasmid containing a (TTAGGG)81 human telomere insert, 7-fold more strand breakage occurred in the restriction fragment with the insert than in a similar-sized control fragment. This result implies that telomeric DNA could protect coding DNA from oxidative damage and might also link oxidative damage and iron load to telomere shortening and aging. In micromolar H2O2, preferential cleavage occurred at the thymidine within the sequence RTGR, a sequence frequently found to be required in promoters for normal responses of many procaryotic and eucaryotic genes to iron or oxygen stress. Computer modeling of the interaction of Fe2+ with RTGR in B-DNA suggests that due to steric hindrance with the thymine methyl, Fe2+ associates in a specific manner with the thymine flipped out from the base stack so as to allow an octahedrally-oriented coordination of the Fe2+ with the three purine N7 residues. Fe2+-dependent changes in NMR spectra of duplex oligonucleotides containing ATGA versus those containing AUGA or A5mCGA were consistent with this model.

Distinct mechanisms of site-specific DNA damage induced by endogenous reductants in the presence of iron(III) and copper(II)

The ability of Cu(II) and Fe(III) to promote site-specific DNA damage in the presence of endogenous reductants was investigated by using 32P-5'-end-labeled DNA fragments obtained from the human p53 tumor suppressor gene and the c-Ha-ras-1 protooncogene. Ascorbate induced metal-dependent DNA damage most efficiently (ascorbate > GSH > NADH). Cu(II) induced endogenous reductants-dependent DNA damage more efficiently than Fe(III). Endogenous reductants plus Fe(III) caused DNA cleavage at every nucleotide, without marked site preference. DNA damage by Fe(III) was inhibited by hydroxyl free radical (.OH) scavengers and catalase. These results suggest that endogenous reductants plus Fe(III) generate free or extremely near free .OH via H2O2 formation, and that .OH causes DNA damage. In the presence of 50 microM Cu(II) in bicarbonate buffer, ascorbate caused DNA cleavage frequently at sites of two or more adjacent guanine residues. In contrast, in the presence of 20 microM Cu(II), ascorbate caused DNA cleavage frequently at thymine residues. Catalase and a Cu(I)-specific chelator inhibited DNA damage by Cu(II), whereas .OH scavengers did not. Fe(III)-dependent 8-oxo-7,8-dihydro-2'-deoxyguanosine formation was inhibited by .OH scavengers, whereas no inhibition by .OH scavengers was observed with Cu(II). These results suggest that .OH is the main active species formed with Fe(III), whereas copper-peroxide complexes with a reactivity similar to .OH participate in Cu(II)-dependent DNA damage. The polyguanosine sequence specificity of DNA damage in the presence of high concentrations of Cu(II) can be explained by the preferential binding of Cu(II) to guanine residues.

The Iron Chelator L1 Potentiates Oxidative DNA Damage in Iron-Loaded Liver Cells

Iron-mediated carcinogenesis is thought to occur through the generation of oxygen radicals. Iron chelators are used in attempts to prevent the long term consequences of iron overload. In particular, 1,2-dimethyl-3-hydroxypyrid-4-one (L1), has shown promise as an effective chelator. Using an established hepatocellular model of iron overload, we studied the generation of iron-catalyzed oxidative DNA damage and the influence of iron chelators, including L1, on such damage. Iron loading of HepG2 cells was found to greatly exacerbate hydrogen peroxide–mediated DNA damage. Desferrithiocin was protective against iron/hydrogen peroxide–induced DNA damage; deferoxamine had no effect. In contrast, L1 exposure markedly potentiated hydrogen peroxide–mediated oxidative DNA damage in iron-loaded liver cells. However, when exposure to L1 was maintained during incubation with hydrogen peroxide, L1 exerted a protective effect. We interpret this as indicating that L1's potential toxicity is highly dependent on the L1:iron ratio. In vitro studies examining iron-mediated ascorbate oxidation in the presence of L1 showed that an L1:iron ratio must be at least 3 to 1 for L1 to inhibit the generation of free radicals; at lower concentrations of L1 increased oxygen radical generation occurs. In the clinical setting, such potentiation of iron-catalyzed oxidative DNA damage at low L1:iron ratios may lead to long-term toxicities that might preclude administration of L1 as an iron chelator. Whether this implication in fact extends to the in vivo situation will have to be verified in animal studies.

The Iron Chelator L1 Potentiates Oxidative DNA Damage in Iron-Loaded Liver Cells

Iron-mediated carcinogenesis is thought to occur through the generation of oxygen radicals. Iron chelators are used in attempts to prevent the long term consequences of iron overload. In particular, 1,2-dimethyl-3-hydroxypyrid-4-one (L1), has shown promise as an effective chelator. Using an established hepatocellular model of iron overload, we studied the generation of iron-catalyzed oxidative DNA damage and the influence of iron chelators, including L1, on such damage. Iron loading of HepG2 cells was found to greatly exacerbate hydrogen peroxide–mediated DNA damage. Desferrithiocin was protective against iron/hydrogen peroxide–induced DNA damage; deferoxamine had no effect. In contrast, L1 exposure markedly potentiated hydrogen peroxide–mediated oxidative DNA damage in iron-loaded liver cells. However, when exposure to L1 was maintained during incubation with hydrogen peroxide, L1 exerted a protective effect. We interpret this as indicating that L1's potential toxicity is highly dependent on the L1:iron ratio. In vitro studies examining iron-mediated ascorbate oxidation in the presence of L1 showed that an L1:iron ratio must be at least 3 to 1 for L1 to inhibit the generation of free radicals; at lower concentrations of L1 increased oxygen radical generation occurs. In the clinical setting, such potentiation of iron-catalyzed oxidative DNA damage at low L1:iron ratios may lead to long-term toxicities that might preclude administration of L1 as an iron chelator. Whether this implication in fact extends to the in vivo situation will have to be verified in animal studies.

Nuclear ferritin protects DNA from UV damage in corneal epithelial cells

Previously, we identified the heavy chain of ferritin as a developmentally regulated nuclear protein of embryonic chicken corneal epithelial cells. The nuclear ferritin is assembled into a supramolecular form indistinguishable from the cytoplasmic form of ferritin found in other cell types and thus most likely has iron-sequestering capabilities. Free iron, via the Fenton reaction, is known to exacerbate UV-induced and other oxidative damage to cellular components, including DNA. Since corneal epithelial cells are constantly exposed to UV light, we hypothesized that the nuclear ferritin might protect the DNA of these cells from free radical damage. To test this possibility, primary cultures of cells from corneal epithelium and stroma, and from skin epithelium and stroma, were UV irradiated, and DNA strand breaks were detected by an in situ 3'-end labeling method. Corneal epithelial cells without nuclear ferritin were also examined. We observed that the corneal epithelial cells with nuclear ferritin had significantly less DNA breakage than other cell types examined. Furthermore, increasing the iron concentration of the culture medium exacerbated the generation of UV-induced DNA strand breaks in corneal and skin fibroblasts, but not in the corneal epithelial cells. Most convincingly, corneal epithelial cells in which the expression of nuclear ferritin was inhibited became much more susceptible to UV-induced DNA damage. Therefore, it seems that corneal epithelial cells have evolved a novel, nuclear ferritin-based mechanism for protecting their DNA against UV damage.

Synergistic DNA damaging effects of malondialdehyde/Cu(II) in PM2 DNA and in human fibroblasts

Malondialdehyde (MDA) is a product of lipid peroxidation (LPO). In combination with CuCl2 MDA induced single strand breaks in PM2 DNA whereas MDA or CuCl2 alone had no effect. Cu(II) oxidized MDA by a radical mechanism under formation of Cu(I). DNA strand break induction was inhibited by catalase (98%), neocuproine (76%) and DMSO (61%). The synergistic damaging effect of MDA and Cu(II) was also demonstrated in human fibroblasts measured by alkaline elution. The combination MDA/CuCl2 caused extensive DNA breakage while neither MDA nor CuCl2 alone induced DNA damage within the cell. Synergistic cytotoxic effects were observed 18 h after a simultaneous treatment of the cells with MDA and CuCl2 for 1 h.

Up-regulation of IGF binding protein-1 as an anticarcinogenic strategy: relevance to caloric restriction, exercise, and insulin sensitivity

The mitotic rate of stem cells is a major determinant of cancer risk. Insulin-like growth factors (IGFs) are virtually obligate stimulants of cell turnover in nearly every tissue. IGF activity is subject to rapid modulation by hepatic release of IGF binding protein-1 (IGFBP-1), a factor whose synthesis is suppressed by insulin and increased by glucagon. Up-regulation of IGFBP-1 production can be expected to decrease IGF activity and thereby diminish cancer risk. Measures that sensitize peripheral tissues to insulin, and thereby down-regulate insulin secretion, can be expected to increase IGFBP-1 synthesis, provided that they do not unduly sensitize hepatocytes as well. Prolonged aerobic exercise and caloric restriction also increase IGFBP-1 production. Since IGF-1 suppresses hepatic synthesis of sex hormone binding globulin (SHBG), down-regulation of IGF activity will increase SHBG levels and thus diminish the availability of free sex hormones--an effect that should further decrease cancer risk in sex hormone-responsive tissues. These considerations rationalize many findings in animal and epidemiologic studies, and suggest that non-diabetic insulin resistance may be a significant cancer risk factor. Increased IGF activity associated with insulin resistance may also promote benign hyperplasias-most notably atherosclerosis. Hyperinsulinemia stimulates intimal hyperplasia indirectly, via IGF.

natural antimutagenic agents may prolong efficacy of human immunodeficiency virus drug therapy

The long-term efficacy of new combination drug therapies for human immunodeficiency virus infection may be limited by the tendency of transfected human immunodeficiency virus to mutate to drug-resistant forms. This argues for the use of safe antimutagenic measures as adjuvants to such therapies. Certain nutrients and food factors-notably selenium, green-tea polyphenols, and cruciferous phytochemicals-can suppress cancer initiation and mutagenesis in animal and cell culture models; epidemiological studies suggest that ambient variations in consumption of these food factors can have an important impact on human cancer rates. Low-fat diets may reduce deoxyribonucleic acid base damage in human leukocytes, whereas increased body iron stores are likely to increase mutation rates. Thus, ample but safe intakes of selenium, green-tea polyphenols, and cruciferous vegetables, in the context of a diet low in fat and assimilable iron, can be expected to prolong the efficacy of drug therapy in subjects infected with the human immunodeficiency virus. These measures can also be recommended for cancer prevention in the general population.

Iron homeostasis, oxidative stress, and DNA damage

Cellular DNA damage under prooxidant conditions has been shown to be mediated by iron. In fact, iron is an important element in the establishment of a prooxidant status in the cell. It is discussed that there exists a mutual dependence between iron metabolism and oxidative stress. Changes in the former by means of genetic manipulation bring about modification in the redox status as judge by oxidative damage in DNA. On the other hand, the induction of a cellular prooxidative condition activates the protein IRP (iron regulatory protein) in a way that renders the cell more able to take up iron. The possible implications of these results is discussed in the light of recent findings reported in the literature on hydrogen peroxide as a signaling species for cell proliferation. The question of DNA strand break formation under prooxidant conditions is reviewed from the viewpoint of which agent is more important: an oxidant generated by Fenton type reaction or Ca2+-activated nucleases. The presence of iron in the nucleus is reviewed. Results have been produced indicating that the larger concentration of this metal in the nucleus, as compared to the cytosol, seems to be explained by an iron-type P-ATPase. There is no explanation, presently, for iron presence in the nucleus, but it certainly imposes a prooxidant trend that needs to be counterbalanced in some way, and evidence is reviewed that nuclear metallothionein plays a role in this regard.

8OHdG levels in brain do not indicate oxidative DNA damage in Alzheimer's disease

Accumulation of oxidative DNA damage has been proposed to underlie aging and neurodegenerative diseases such as Alzheimer's Disease (AD). The DNA adduct 8-hydroxy-2'-deoxyguanosine (8OHdG) is considered a good indicator of oxidative DNA damage. To investigate whether this type of DNA damage is involved in AD etiology, 8OHdG levels were determined in postmortem human brain tissue of controls and AD patients (in frontal, occipital, and temporal cortex and in hippocampal tissue). Parametric studies in rat revealed no influences of postmortem delay, repeated freezing/thawing or storage time. In human brain, approximately two 8OHdG molecules were present per 10(5) 2'-deoxyguanosines. In AD patients and controls, 8OHdG-levels were not related to age, sex, or brain region. Also, no differences were found between controls and AD patients. It was concluded that 8OHdG in nuclear DNA, although present throughout the brain in fairly high amounts, does not accumulate with age, nor does it appear to be involved in AD. More detailed studies are required to extend this conclusion to other types of oxidative damage.

Arsenite induces apoptosis in Chinese hamster ovary cells by generation of reactive oxygen species

Arsenic, a human carcinogen, possesses a serious environmental threat but the mechanism of its toxicity remains unclear. Knowledge of how arsenic induces cell death and how cells escape the death path may help to understand arsenic carcinogenesis. We have investigated the nature of sodium arsenite-induced cell death in Chinese hamster ovary K1 cells. Following phosphate-citric acid buffer extraction, apoptotic cells with lower DNA content than the G1 cells were detected by flow cytometry. Immediately after 4 h of 40 microM arsenite treatment, no appreciable fraction of cells with sub-G1 DNA content was detected; however, the sub-G1 cell fraction increased with postarsenite incubation time, and detectable increase started at 8 h of incubation, whereas the intracellular peroxide level as measured by the fluorescent intensity of 2',7'-dichlorofluorescein increased immediately following a 4-h arsenite treatment. Simultaneous treatment with arsenite plus antioxidant (N-acetyl-cysteine, Trolox, and Tempo); copper ion chelator (neocuproine); protein kinase inhibitor (H-7) or protein synthesis inhibitor (cycloheximide) reduced the fraction of sub-G1 cell and internucleosomal DNA degradation. Trolox, neocuproine, or cycloheximide given after arsenite treatment also effectively reduced apoptosis. These results lead to a working hypothesis that arsenite-induced apoptosis in CHO-K1 cells is triggered by the generation of hydrogen peroxide, followed by a copper-mediated Fenton reaction that catalyzes the production of hydroxyl radicals, which selectively activates protein kinase through de novo synthesis of macromolecules.

DNA single and double strand breaks induced by aliphatic and aromatic aldehydes in combination with copper (II)

The aliphatic n-butyr-and n-valeraldehyde as well as the aromatic benz- and anisaldehyde induced DNA strand breaks in PM2 DNA in the presence of CuCl2. Neither aldehydes nor CuCl2 alone showed DNA breakage properties. The maximum of single strand breaks (SSBs) induced by the combination of CuCl2 and aldehydes was dependent on the CuCl2-concentration. The aliphatic aldehydes induced SSBs and double strand breaks (DSBs) at lower concentrations than aromatic aldehydes when optimal CuCl2 concentration were used. Catalase and neocuproine nearly completely inhibited strand break formation induced by aromatic aldehydes/CuCl2. The prevention of strand breaks induced by aliphatic aldehydes/CuCl2 was less effective. While the inhibition by neocuproine was only 25%, catalase was totally ineffective. In all aldehydes/CuCl2 mixtures the formation of Cu(I) was observed. The results point to different DNA damaging species produced during redox reactions of aromatic and aliphatic aldehydes in combination with CuCl2.

Enhancement of oxidative cleavage of DNA by the binding sites of two anti-double-stranded DNA antibodies

Nucleic acid specificity was tested for two monoclonal anti-double-stranded DNA autoantibodies, 2C10 and H241, derived from two lupus-prone MRL/Mp-lpr/lpr mice. Antibody 2C10 bound double-stranded oligonucleotides with a preference for dA-dT over dG-dC base pairs and did not bind single-stranded oligonucleotides. Distamycin A, an antibiotic that binds to the minor groove, inhibited 2C10 binding of double-stranded DNA, suggesting that this antibody interacts with dA-dT base pairs in the minor groove. Antibody H241 binding was previously shown to have a dG-dC preference and to involve both major and minor grooves. In attempted footprinting assays, both 2C10 and H241 markedly en- hanced rather than protected against cleavage of DNA by hydroxyl radical-generating systems. With 2C10, this enhancement effect was observed only when hydroxyl radical generation was associated with oxidation of Fe(II). In contrast, H241 enhancement occurred in the presence of H2O2 and ascorbate or UV light irradiation and did not depend on added metal ion. The enhancement sites were related to the antibody binding specificities. The oligonucleotide 5'-AAAATATATATTT-3' was a much more effective inhibitor of the 2C10 enhancement than of the H241 effect, whereas the oligonucleotide 5'-GGGGCGCGCGCCC-3' was a much more effective inhibitor of the H241 enhancement. In addition, the enhanced cleavage occurred preferentially at dA-dT-rich regions with 2C10 and at dG-dC-rich regions with H241. These findings raise the possibility that anti-DNA autoantibodies could enhance DNA damage in inflammatory lesions in which hydroxyl radicals are generated.

N,N'-bis-(3,4,5-trimethoxybenzyl) ethylenediamine N,N'-diacetic acid as a new iron chelator with potential medicinal applications against oxidative stress

N,N'-bis-(3,4,5-trimethoxybenzyl) ethylenediamine N,N,-diacetic acid dihydrochloride (OR10141) is a member of a recently described series of "oxidative stress activatable iron chelators." These chelators have a relatively low affinity for iron but can be site-specifically oxidized, in situations mimicking oxidative stress in vitro, into species with strong iron-binding capacity. It is hoped that this local activation process will minimise toxicity compared to strong iron chelators that may interfere with iron metabolism. The present paper describes the results of experiments aimed at characterising oxidative reactions between iron-OR10141 complexes and hydrogen peroxide. Incubation of ascorbate and hydrogen peroxide with the ferric chelate of OR10141 in neutral aqueous solution yields a purple solution with a chromophore at 560 nm, which is consistent with an o-hydroxylation of one of the trimethoxybenzyl rings. Oxidation of OR10141 also takes place, although more slowly, by incubating hydrogen peroxide with ferric OR10141 complex in the absence of reductant. HPLC analysis shows that OR10141 is consumed during the reaction and transformed principally into N-(2-hydroxy 3,4,5-trimethoxybenzyl) N'-(3,4,5-trimethoxybenzyl) ethylenediamine N,N'-diacetic acid. Minor products are also formed, some of which were identified by mass spectrometry. The protective effect of OR10141 in vitro against DNA single strand breaks, protein damage, and lipid peroxidation induced by Fenton chemistry suggests that this compound is able to compete for iron with biological molecules and, thus, that this strategy of protection against oxidative stress is feasible. In addition, preliminary results showing protective effects of OR10141 dimethyl ester against toxicity induced by hydrogen peroxide in cell culture are described. It is concluded that OR10141 and related prodrugs might be useful in vivo in chronic situations involving oxidative stress.

DNA strand breaks produced by oxidative stress in mammalian cells exhibit 3'-phosphoglycolate termini

In recent years two mechanisms have been proposed for the production of DNA strand breaks in cells undergoing oxidative stress: (i) DNA attack by OH radical, produced by Fenton reaction catalyzed by DNA-bound iron; and (ii) DNA attack by calcium-activated nucleases, due to the increase of cytosolic and nuclear calcium induced by oxidative stress. We set out to investigate the participation of the former mechanism by detecting and quantifying 3'-phosphoglycolate, a 3' DNA terminus known to be formed by OH radical attack to the deoxyribose moiety, followed by sugar ring rupture and DNA strand rupture. These structures were found in DNA of monkey kidney cells exposed to hydrogen peroxide, iron nitrilotriacetate or ascorbate, all species known to favor a cellular pro-oxidant status. The method employed to measure 3' phosphoglycolate was the 32P-postlabeling assay. Repair time course experiments showed that it takes 10 h for 3'-phosphoglycolate to be removed from DNA. It was found that the DNA of both control cells and cells exposed to hydrogen peroxide had a very poor capacity of supporting in vitro DNA synthesis, catalyzed by DNA polymerase I. If the DNA was previously incubated with exonuclease III, an enzyme able to expose 3'-OH primers by removal of 3'-phosphoglycolate and 3'-phosphate termini the in vitro synthesis was substantially increased. This result shows that either of these termini are present at the break and that 3'-hydroxyl termini are virtually absent. At least 25% of the strand breaks exhibited 3'-phosphoglycolate termini as determined by the 32P-postlabeling assay, but due to the characteristic of the method this percentage is likely to be higher. These results favor the hypothesis that an oxidative agent generated by Fenton reaction is responsible for DNA strand breakage in cells undergoing oxidative stress.

Content of iron and copper in the nuclei and induction of pH 9-labile lesions in L5178Y sublines inversely cross-sensitive to H2O2 and x-rays

Cells from the L5178Y murine lymphoma subline LY-R are twice as resistant to killing by ionizing radiation than the subline LY-S. In contrast, LY-R cells are more sensitive to killing by H2O2, the effect being more pronounced at 37 degrees C than 0 degree C. Initial DNA damage after H2O2 treatment (both temperatures, 5 min) has been estimated by the 'comet' assay (single-cell gel electrophoresis) and fluorescent halo technique. According to both methods, the initial damage is significantly higher in LY-R cells, particularly that inflicted at 0 degree C. Differences between DNA unwinding and rewinding abilities at pH 9 and 6.9 (estimated by the fluorescent halo technique) point to a considerable difference in pH-9-labile damage between the sublines, as observed previously for x-irradiated cells (Kapiszewska et al. 1992). In contrast to findings with x-irradiated cells, however, after H2O2 treatment this damage is more extensive in LY-R cells than in LY-S cells. Thus, the initial pH-9-labile damage corresponds to the pattern of sensitivity to H2O2 and x-rays. We suggest that this is caused by different proportions of cuprous and ferric ions found in the nuclei of LY sublines and by the different ability of these ions to react with H2O2 and water radiolysis products. The copper/iron ratio in the nucleus is 1.31 in LY-R cells and 4.84 in LY-S cells.

Oxidative stress and living cells

The review deals with the effects of reactive oxygen species, both radical and nonradical (e.g. hydrogen peroxide), on cells and organisms. The chemical and biochemical aspects include description of individual reactive oxygen species, chemical reactions giving rise to them, their interconversions and interactions with metals (Fe2+, Cu2+, Cu+) and other substances (scavengers, antioxidants). The biological aspects concern the specific features and locations of cellular enzyme systems involved in radical production and/or removal. Major harmful effects of the species on the molecular (protein oxidation, lipid peroxidation, damage to DNA) and cellular level (effect on signal transduction, on cell membrane functions and on gene expression) are surveyed. Methods whereby cells and organisms cope with the onslaught of these reactive species are reviewed as well as implications for plant, animal and human health.

Comparison of effects of iron and calcium chelators on the response of L5178Y sublines to X-rays and H2O2

The L5178Y murine lymphoma subline LY-R is twofold more resistant to killing by ionizing radiation than the subline LY-S. In contrast, LY-R cells are more sensitive to killing by hydrogen peroxide: at 37 degrees C LY-R cells are 1.4 times more sensitive to the killing effect of H2O2 than LY-S cells. Pretreatment with the iron chelator desferroxamine followed by hydrogen peroxide treatment at 37 degrees C gives a considerable sparing effect, which is substantially greater for the LY-R subline than for the LY-S subline. This is reflected in the initial DNA damage (estimated by single cell gel electrophoresis), survival and mutation frequency in the HGPRT locus. Similar results have been obtained with calcium chelators, which, according to recent findings (Sandström and Granström 1993), also are efficient iron chelators. In contrast, the response to X-rays is not modified by the above chelators, with the exception of mutation frequencies: lower mutant numbers are found in desferroxamine pretreated LY-R cells.

A role for metals and free radicals in the induction of apoptosis in thymocytes

Recent reports have implicated a possible but undefined role for reactive oxygen species in the induction and mediation of apoptosis. In the present study, the role of free radicals and metal ions in apoptosis induced in rat thymocytes by dexamethasone and etoposide was examined. Copper chelators, but not iron specific chelators, inhibited apoptosis induced by both these stimuli. Several antioxidants also possessed potent inhibitory effects. We therefore propose that diverse agents may induce apoptosis in thymocytes by a common mechanism involving a copper mediated Fenton reaction, generating site specific hydroxyl radicals, possibly as a result of activation of the redox sensitive transcription factor NF-kappa B.