DNA damage by superoxide-generating systems in relation to the mechanism of action of the anti-tumour antibiotic adriamycin

Photo-activated proflavine degrades protein and impairs enzyme activity: Involvement of hydroxyl radicals

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Generation of hydroxyl radical (·OH) increased by proflavine upon illumination with fluorescent light.

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Proflavine resulted in oxidative modifications and degradation of protein and enzyme structure.

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The addition of Cu (II) augmented photo-illuminated proflavine to generate hydroxyl radicals.

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Proflavine-induced hydroxyl radicals have a deleterious influence on protein and enzyme activity.

Proflavine is a well-known antiseptic and bacteriostatic drug, however, it has the potential to be hazardous and mutagenic. Proflavine enters cells and intercalates between DNA base pairs, resulting in mutation and replication inhibition. Previously several investigators demonstrated that photo-activated proflavine generated double-stranded DNA breakage and protein structural alterations. The present study investigated the role of hydroxyl radical (·OH) due to activation of proflavine in the breakdown of protein and enzyme by photo-activated proflavine. The results show that the formation of hydroxyl radicals increased as the photo-illumination period increased, as did the concentrations of proflavine and Cu (II). As demonstrated by SDS-PAGE, the excess of free radicals due to proflavine resulted in oxidative modifications and degradation of BSA protein and trypsin enzyme. Additionally, with an increase in Cu (II) concentration, photo-illuminated proflavine induced a considerable loss of enzyme activity and also accelerated the degradation of the enzyme. Bathocuproine, a particular Cu (I)-sequestering agent, prevented protein degradation and enzyme inactivation. Hydroxyl radical scavengers inhibited the protein-damaging process, indicating that hydroxyl radicals play a substantial role in protein damage. The tryptophan moiety was quenched by proflavine, demonstrating that it binds to proteins and enzymes, changing their structure and activity. As a result, this study helps to better understand proflavine's deleterious influence on protein and enzyme degradation by oxygen-free radicals.

Coenzyme Q10 for Prevention of Anthracycline-Induced Cardiotoxicity

Preclinical and clinical studies suggest that anthracycline-induced cardiotoxicity can be prevented by administering coenzyme Q10 during cancer chemotherapy that includes drugs such as doxorubicin and daunorubicin. Studies further suggest that coenzyme Q10 does not interfere with the antineoplastic action of anthracyclines and might even enhance their anticancer effects. Preventing cardiotoxicity might allow for escalation of the anthracycline dose, which would further enhance the anticancer effects. Based on clinical investigation, although limited, a cumulative dose of doxorubicin of up to 900 mg/m2, and possibly higher, can be administered safely during chemotherapy as long as coenzyme Q10 is administered concurrently. The etiology of the dose-limiting cardiomyopathy that is induced by anthracyclines can be explained by irreversible damage to heart cell mitochondria, which differ from mitochondria of other cells in that they possess a unique enzyme on the inner mitochondrial membrane. This enzyme reduces anthracyclines to their semiquinones, resulting in severe oxidative stress, disruption of mitochondrial energetics, and irreversible damage to mitochondrial DNA. Damage to mitochondrial DNA blocks the regenerative capability of the organelle and ultimately leads to apoptosis or necrosis of myocytes. Coenzyme Q10, an essential component of the electron transport system and a potent intracellular antioxidant, appears to prevent damage to the mitochondria of the heart, thus preventing the development of anthracycline-induced cardiomyopathy.

The maintenance of mitochondrial DNA integrity--critical analysis and update

DNA molecules in mitochondria, just like those in the nucleus of eukaryotic cells, are constantly damaged by noxious agents. Eukaryotic cells have developed efficient mechanisms to deal with this assault. The process of DNA repair in mitochondria, initially believed nonexistent, has now evolved into a mature area of research. In recent years, it has become increasingly appreciated that mitochondria possess many of the same DNA repair pathways that the nucleus does. Moreover, a unique pathway that is enabled by high redundancy of the mitochondrial DNA and allows for the disposal of damaged DNA molecules operates in this organelle. In this review, we attempt to present a unified view of our current understanding of the process of DNA repair in mitochondria with an emphasis on issues that appear controversial.

Pro-oxidants ameliorate radiation-induced apoptosis through activation of the calcium-ERK1/2-Nrf2 pathway

There are no reports describing the ability of pro-oxidants to protect against radiation-induced apoptosis. Activation of the redox-sensitive transcription factor Nrf2 by low levels of ROS is known to protect against oxidative stress-induced cell death. In this study, hydrogen peroxide, diethylmaleate, and 1,4-naphthoquinone (NQ) exhibited complete protection against radiation-induced cell death in lymphocytes as estimated by propidium iodide staining. Radioprotection by NQ was demonstrated by inhibition of caspase activation, decrease in cell size, DNA fragmentation, nuclear blebbing, and clonogenic assay. Interestingly, NQ offered protection to lymphocytes even when added to cells postirradiation. NQ increased intracellular ROS levels and decreased GSH levels. NQ activated Nrf2 and increased the expression of the cytoprotective gene heme oxygenase-1 in lymphocytes. NQ increased ERK phosphorylation, which is upstream of Nrf2, and this ERK activation was through increased intracellular calcium levels. Administration of NQ to mice offered protection against whole-body irradiation (WBI)-induced apoptosis in splenic lymphocytes and loss of viability of spleen and bone marrow cells. It restored WBI-mediated changes in hematological parameters and functional responses of lymphocytes. Importantly, NQ rescued mice against WBI-induced mortality. These results demonstrated that a pro-oxidant such as NQ can protect against radiation-induced apoptosis by activation of multiple prosurvival mechanisms including activation of the calcium-ERK1/2-Nrf2 pathway.

Is there more to aging than mitochondrial DNA and reactive oxygen species?

With the aging of the population, we are seeing a global increase in the prevalence of age-related disorders, especially in developed countries. Chronic diseases disproportionately affect the older segment of the population, contributing to disability, a diminished quality of life and an increase in healthcare costs. Increased life expectancy reflects the success of contemporary medicine, which must now respond to the challenges created by this achievement, including the growing burden of chronic illnesses, injuries and disabilities. A well-developed theoretical framework is required to understand the molecular basis of aging. Such a framework is a prerequisite for the development of clinical interventions that will constitute an efficient response to the challenge of age-related health issues. This review critically analyzes the experimental evidence that supports and refutes the Free Radical/Mitochondrial Theory of Aging, which has dominated the field of aging research for almost half a century.

Juglone, a naphthoquinone from walnut, exerts cytotoxic and genotoxic effects against cultured melanoma tumor cells

This study demonstrates cytotoxic and genotoxic potential of juglone, a chief constituent of walnut, and its underlying mechanisms against melanoma cells. MTT assay and clonogenic assay were used to study cytotoxicity, micronucleus assay to assess genotoxicity, glutathione (GSH) assay and 2',7'-dicholorofluorescein diacetate (DCFH-DA) assay to evaluate the oxidative stress induction. Apoptosis/necrosis induction was analysed by flow cytometry. We observed a concentration-dependent decrease in cell survival with a corresponding increase in the lactate dehydrogenase levels. A dose-dependent increase in the frequency of micronucleated binucleate cells indicated the potential of juglone to induce cytogenetic damage in melanoma tumor cells. Moreover, results of the micronuclei study indicated division delay in the proliferating cell population by showing decrease in the cytokinesis blocked proliferation index. Further, juglone-induced apoptosis and necrosis could be demonstrated by oligonucleosomal ladder formation, microscopic analysis, increase in the hypodiploid fraction (sub Go peak in DNA histogram), as well as an increased percentage of AnnexinV(+)/PI(+) cells detected by flow cytometry. A significant concentration-dependent decrease in the glutathione levels and increase in dichlorofluorescein (DCF) fluorescence after juglone treatment confirmed the ability of juglone to generate intracellular reactive oxygen species. The cytotoxic effect of juglone can be attributed to mechanisms including the induction of oxidative stress, cell membrane damage, and a clastogenic action leading to cell death by both apoptosis and necrosis.

Structure and function of "metalloantibiotics"

Although most antibiotics do not need metal ions for their biological activities, there are a number of antibiotics that require metal ions to function properly, such as bleomycin (BLM), streptonigrin (SN), and bacitracin. The coordinated metal ions in these antibiotics play an important role in maintaining proper structure and/or function of these antibiotics. Removal of the metal ions from these antibiotics can cause changes in structure and/or function of these antibiotics. Similar to the case of "metalloproteins," these antibiotics are dubbed "metalloantibiotics" which are the title subjects of this review. Metalloantibiotics can interact with several different kinds of biomolecules, including DNA, RNA, proteins, receptors, and lipids, rendering their unique and specific bioactivities. In addition to the microbial-originated metalloantibiotics, many metalloantibiotic derivatives and metal complexes of synthetic ligands also show antibacterial, antiviral, and anti-neoplastic activities which are also briefly discussed to provide a broad sense of the term "metalloantibiotics."

Hedgehog in the human: a possible explanation for the VATER association

Foregut malformations are relatively common anomalies, occurring in 1 in 2000-5000 live births. The adriamycin-induced rat model of the VATER association has provided a means of studying the morphogenesis of a variety of major congenital structural abnormalities similar to those seen in humans with VATER association. The secreted glycoprotein, Sonic hedgehog (Shh), may act as an endodermal signal that controls gut and lung patterning. Mice with targeted deletion of Shh have foregut defects that are consistent with those produced by administration of adriamycin. It is possible that mutations induced by adriamycin may result from the breakdown of the Shh signalling pathway.

Cloning and characterization of three differentially expressed peroxidoxin genes from Leishmania chagasi. Evidence for an enzymatic detoxification of hydroxyl radicals

Antioxidants have been implicated in protecting cells from oxygen radicals produced as a result of aerobic metabolism and in response to foreign pathogens by phagocytic cells. The mechanisms allowing pathogens to withstand the toxic prooxidant environment within the phagolysosome are poorly understood. We have cloned and characterized three antioxidant genes belonging to the 2-Cys family of peroxidoxins from Leishmania chagasi that may prove to provide these parasites with an enhanced defense mechanism against toxic oxidants. The 5'-untranslated regions and coding regions of each gene are highly conserved, whereas the 3'-untranslated regions have diverged significantly. L. chagasi peroxidoxin 1 (LcPxn1) is predominantly expressed in the amastigote stage, whereas LcPxn2 and LcPxn3 are expressed mainly in the promastigote stage, with LcPxn3 being far less abundant than LcPxn2. LcPxn2 and LcPxn3 possess a nine-amino acid extension at the carboxyl terminus, which LcPxn1 lacks. LcPxn1 appears to exist as high molecular weight multimers in vivo, and recombinant LcPxn1 was shown to detoxify hydrogen peroxide and alkyl hydroperoxides. We also present strong evidence that recombinant LcPxn1 can enzymatically detoxify hydroxyl radicals, an activity never before clearly demonstrated for a protein.

Multiprobe RNase protection assay analysis of mRNA levels for the Escherichia coli oxidative DNA glycosylase genes under conditions of oxidative stress

Escherichia coli formamidopyrimidine DNA glycosylase (Fpg), MutY DNA glycosylase, endonuclease VIII, and endonuclease III are oxidative base excision repair DNA glycosylases that remove oxidized bases from DNA, or an incorrect base paired with an oxidized base in the case of MutY. Since genes encoding other base excision repair proteins have been shown to be part of adaptive responses in E. coli, we wanted to determine whether the oxidative DNA glycosylase genes are induced in response to conditions that cause the type of damage their encoded proteins remove. The genes fpg, mutY, nei, and nth encode Fpg, MutY, endonuclease VIII, and endonuclease III, respectively. Multiprobe RNase protection assays were used to examine the transcript levels of these genes under conditions that induce the SoxRS, OxyR, and SOS regulons after a shift from anaerobic to aerobic growth and at different stages along the growth curve. Transcript levels for all four genes decreased as cells progressed from log-phase growth to stationary phase and increased after cells were shifted from anaerobic to aerobic growth. None of the genes were induced by hydrogen peroxide, paraquat, X rays, or conditions that induce the SOS response.

Pro-oxidant, anti-oxidant and cleavage activities on DNA of curcumin and its derivatives demethoxycurcumin and bisdemethoxycurcumin

Curcumin, a naturally occurring phytochemical responsible for the colour of turmeric shows a wide range of pharmacological properties including antioxidant, anti-inflammatory and anti-cancer effects. We have earlier shown that curcumin in the presence of Cu(II) causes strand cleavage in DNA through generation of reactive oxygen species, particularly the hydroxyl radical. Thus, curcumin shows both antioxidant as well as pro-oxidant effects. In order to understand the chemical basis of various biological properties of curcumin, we have studied the structure-activity relationship between curcumin and its two naturally occurring derivatives namely demethoxycurcumin (dmC) and bisdemethoxycurcumin (bdmC). Curcumin was found to be the most effective in the DNA cleavage reaction and a reducer of Cu(II) followed by dmC and bdmC. The rate of formation of hydroxyl radicals by the three curcuminoids also showed a similar pattern. The relative antioxidant activity was examined by studying the effect of these curcuminoids on cleavage of plasmid DNA by Fe(II)-EDTA system (hydroxyl radicals) and the generation of singlet oxygen by riboflavin. The results indicate that curcumin is considerably more active both as an antioxidant as well as an oxidative DNA cleaving agent. The DNA cleavage activity is the consequence of binding of Cu(II) to various sites on the curcumin molecule. Based on the present results, we propose three binding sites for Cu(II). Two of the sites are provided by the phenolic and methoxy groups on the two benzene rings and the third site is due to the presence of 1,3-diketone system between the rings. Furthermore, both the antioxidant as well as pro-oxidant effects of curcuminoids are determined by the same structural moieties.

Mammalian small stress proteins protect against oxidative stress through their ability to increase glucose-6-phosphate dehydrogenase activity and by maintaining optimal cellular detoxifying machinery

The protective activity of small stress proteins (sHsp) against H2O2-mediated cell death in the highly sensitive murine L929 fibroblast has been analyzed. We report here that the human Hsp27- and murine Hsp25-mediated rise in glutathione (GSH) levels as well as the maintenance of this redox modulator in its reduced form was directly responsible for the protection observed at the level of cell morphology and mitochondrial membrane potential. sHsp expression also buffered the increase in protein oxidation following H2O2 treatment and protected several key enzymes against inactivation. In this case, however, the protection necessitated both an increase in GSH and the presence of sHsp per se since the pattern of protection against protein oxidation mediated by a simple GSH increase was different from that induced by sHsp expression. Among the enzymes analyzed, we noticed that sHsp significantly increased glucose-6-phosphate dehydrogenase (G6PD) activity and to a lesser extent glutathione reductase and glutathione transferase activities. Moreover, an increased GSH level was observed in G6PD-overexpressing L929 cell clones. Taken together our results suggest that sHsp protect against oxidative stress through a G6PD-dependent ability to increase and uphold GSH in its reduced form and by using this redox modulator as an essential parameter of their in vivo chaperone activity against oxidized proteins.

Uric acid inhibits L-DOPA-CU(II) mediated DNA cleavage

It has been proposed that considerable DNA damage may be caused by endogenous metabolites produced during the body's normal metabolic processes. We have previously shown that L-DOPA, in the presence of Cu(II) leads to oxidative DNA breakage in vitro. Uric acid is considered to be a naturally occuring antioxidant and is present in plasma at a relatively high concentration. In this paper we report that uric acid inhibits L-DOPA-Cu(II) mediated DNA cleavage at concentrations similar to or lower than those found in plasma. Xanthine, which is the structural analogue of uric acid is a more potent inhibitor of the reaction. Uric acid was also shown to directly quench the generation of hydroxyl radicals by L-DOPA-Cu(II). The results have been discussed in relation to the putative protective role of uric acid against endogenous DNA damage by oxygen radicals.

Enhancement of daunomycin toxicity by the differentiation inducer hexamethylene bisacetamide in erythroleukemia cells

Cytotoxic effects of daunomycin were investigated upon differentiation of Friend erythroleukemia cells induced with hexamethylene bisacetamide, a process during which a 20-fold increase in the hemoglobin content occurred. Daunomycin proved to be more toxic to differentiated Friend cells than to their undifferentiated counterparts. No changes in the daunomycin uptake rates of the two cell types were detectable. Externally added catalase and desferrioxamine mesylate protected against the additional cytotoxicity of daunomycin in differentiated cells, pointing to hydrogen peroxide and iron ions as mediators of the toxic effect. Daunomycin-dependent, cyanide-insensitive oxygen consumption of control and induced cells did not differ significantly, and the rate of formation of the daunomycin semiquinone radical electron paramagnetic resonance signal was similar in both cell types, indicating that the difference in toxicity was not due to increased drug activation by plasma membrane enzymes. Differentiated cells had a lowered catalase content; the cellular iron content was shown to increase by 2.8-fold upon cell differentiation, with hemoglobin-bound iron being about 50% of the total. Altogether, the results suggest increased intracellular hydrogen peroxide generation mediated by hemoglobin, combined with a decrease in catalase activity and an increase in accessible iron, as responsible for the higher sensitivity to daunomycin shown by differentiated Friend cells. This represents the first experimental system where the increase in anthracycline cytotoxicity upon cell differentiation can be attributed to redox activation and the formation of reactive oxygen species.

International Commission for Protection Against Environmental Mutagens and Carcinogens. Oxidative DNA damage--the effects of certain genotoxic and operationally non-genotoxic carcinogens

A wide variety of oxidative DNA lesions are commonly present in untreated human and animal DNA. One of these lesions, 8-hydroxydeoxyguanosine, has been shown to lead to base mispairing (mutation) on DNA replication. Other lesions remain to be investigated in this respect. Oxidative DNA lesions on cell replication may, in appropriate circumstances, lead to proto-oncogene activation. Oxidative DNA damage, on fixation, may also lead to cytotoxicity followed by regenerative proliferation. The probable or possible importance of oxidative DNA damage is reviewed for various classes of carcinogens and natural processes, including metal ions, high-energy radiation, miscellaneous chemicals, tumor-promoting agents, polyhydroxyphenols/quinones, lipid metabolism, peroxisome proliferators and thyroid function. It is concluded that although the evidence needs considerable strengthening in many of these examples, the available information indicates the potential importance of oxidative DNA damage in the induction of tumors by these agents. It is also possible that non-cancerous degenerative diseases associated with aging are the result of the accumulation of lesions resulting from unrepaired oxidative DNA damage.

Effect of ascorbate on adriamycin-Fe(3+)-induced lipid peroxidation and DNA damage

Adriamycin-Fe(3+)-induced lipid peroxidation was enhanced by ascorbate at low concentrations. High concentrations of ascorbate also enhanced the peroxidation reaction, but only at an early stage. The initial rate of peroxidation depended upon the ratio of adriamycin-Fe2+/adriamycin-Fe3+ and the maximum rate was observed at the ratio of 1:1. These results suggest that the adriamycin-Fe(3+)-induced lipid peroxidation may be initiated by an adriamycin-Fe(2+)-oxygen-adriamycin-Fe3+ complex. Ascorbate also promoted bathophenanthroline-Fe2+ formation from adriamycin-Fe3+ in a dose-dependent manner. It seems likely that ascorbate influences the peroxidation reaction via the reduction of adriamycin-Fe3+. During the interaction of adriamycin-Fe3+ with ascorbate, deoxyribose was not degraded, suggesting that hydroxyl radical formation did not occur. In contrast, plasmid PM2 DNA was readily damaged during the interaction of adriamycin-Fe3+ with ascorbate. Catalase, mannitol and dimethylsulfoxide prevented DNA damage. No DNA damage occurred when the reaction was run under nitrogen gas, indicating that oxygen is involved.

Doxorubicin-mediated free radical generation in intact human tumor cells enhances nitroxide electron paramagnetic resonance absorption intensity decay

The decay of nitroxide spin label electron paramagnetic resonance (EPR) absorption intensity was used to investigate the doxorubicin-mediated intracellular generation of free radicals. The effects of 50-500 micrograms/ml doxorubicin on human tumor cells (MCF-7, breast cancer cells, and HL-60, promyelocytic leukemia, cells) were studied by measuring 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) absorption intensity decay (TAID) at a TEMPO concentration of 10 microM. Doxorubicin accelerated the TAID in both cell lines with a detection limit of 50 micrograms/ml for MCF-7 cells and 500 micrograms/ml doxorubicin for HL-60 cells. Preincubation of cells with the iron chelating agent, deferoxamine (5 mM), partially prevented the effects of doxorubicin on the TAID. Catalase and copper, zinc-superoxide dismutase (Cu,Zn-SOD) had no influence on the effects of doxorubicin on the TAID in intact cells. However, Cu,Zn-SOD completely abolished the effects of doxorubicin on the TAID in a MCF-7 cell-free system. Our findings suggest that doxorubicin mediates the intracellular generation of O2.- and that iron is involved in this process.

Induction of oxidative single- and double-strand breaks in DNA by ferric citrate

The relative risk of primary hepatocellular carcinoma in genetic hemochromatosis (GH) is estimated at over 200 times as that of control populations. Recently, ferric ion chelated to citrate (Fe-citrate) was identified as the major non-transferrin-bound iron in the serum of GH patients. We investigated whether low concentration of Fe-citrate plus reductant could damage supercoiled plasmid DNA under physiological pH and ionic strength. Incubation of Fe-citrate with either H2O2, L-ascorbate, or L-cysteine induced single- and double-strand breaks in supercoiled plasmid pZ189 in a concentration- and time-dependent fashion. DNA strand breaks produced by Fe-citrate plus H2O2 increased at reduced pH (< or = 6.9). Catalase and free radical scavengers inhibited the DNA breakage produced by Fe-citrate in combination with each reductant, suggesting that H2O2 and finally .OH are responsible DNA damaging species. The catalytic ability of Fe-citrate to induce DNA strand breaks, particularly double-strand breaks (DSBs), may contribute to the carcinogenic processes observed in GH.

Redox cycling of potential antitumor aziridinyl quinones

The formation of reactive oxygen intermediates (ROI) during redox cycling of newly synthesized potential antitumor 2,5-bis (1-aziridinyl)-1,4-benzoquinone (BABQ) derivatives has been studied by assaying the production of ROI (superoxide, hydroxyl radical, and hydrogen peroxide) by xanthine oxidase in the presence of BABQ derivatives. At low concentrations (< 10 microM) some BABQ derivatives turned out to inhibit the production of superoxide and hydroxyl radicals by xanthine oxidase, while the effect on the xanthine-oxidase-induced production of hydrogen peroxide was much less pronounced. Induction of DNA strand breaks by reactive oxygen species generated by xanthine oxidase was also inhibited by BABQ derivatives. The DNA damage was comparable to the amount of hydroxyl radicals produced. The inhibiting effect on hydroxyl radical production can be explained as a consequence of the lowered level of superoxide, which disrupts the Haber-Weiss reaction sequence. The inhibitory effect of BABQ derivatives on superoxide formation correlated with their one-electron reduction potentials: BABQ derivatives with a high reduction potential scavenge superoxide anion radicals produced by xanthine oxidase, leading to reduced BABQ species and production of hydrogen peroxide from reoxidation of reduced BABQ. This study, using a unique series of BABQ derivatives with an extended range of reduction potentials, demonstrates that the formation of superoxide and hydroxyl radicals by bioreductively activated antitumor quinones can in principle be uncoupled from alkylating activity.

Substrate specificity of the Escherichia coli Fpg protein (formamidopyrimidine-DNA glycosylase): excision of purine lesions in DNA produced by ionizing radiation or photosensitization

We have investigated the excision of a variety of modified bases from DNA by the Escherichia coli Fpg protein (formamidopyrimidine-DNA glycosylase) [Boiteux, S., O'Connor, T. R., Lederer, F., Gouyette, A., & Laval, J. (1990) J. Biol. Chem. 265, 3916-3922]. DNA used as a substrate was modified either by exposure to ionizing radiation or by photosensitization using visible light in the presence of methylene blue (MB). The technique of gas chromatography/mass spectrometry, which can unambiguously identify and quantitate pyrimidine- and purine-derived lesions in DNA, was used for analysis of hydrolyzed and derivatized DNA samples. Thirteen products resulting from pyrimidines and purines were detected in gamma-irradiated DNA, whereas only the formation of 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua) and 8-hydroxyguanine (8-OH-Gua) was observed in visible light/MB-treated DNA. Analysis of gamma-irradiated DNA after incubation with the Fpg protein followed by precipitation revealed that the Fpg protein significantly excised 4,6-diamino-5-formamidopyrimidine (FapyAde), FapyGua, and 8-OH-Gua. The excision of a small but detectable amount of 8-hydroxyadenine was also observed. The detection of these products in the supernatant fractions of the same samples confirmed their excision by the enzyme. Nine pyrimidine-derived lesions were not excised. The Fpg protein also excised FapyGua and 8-OH-Gua from visible light/MB-treated DNA. The presence of these products in the supernatant fractions confirmed their excision.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA damage by oxygen-derived species. Its mechanism and measurement in mammalian systems

When cells are exposed to oxidative stress, DNA damage frequently occurs. The molecular mechanisms causing this damage may include activation of nucleases and direct reaction of hydroxyl radicals with the DNA. Several oxygen-derived species can attack DNA, producing distinctive patterns of chemical modification. Observation of these patterns and measurement of some of the products formed has been used to determine the role of different oxygen-derived species in DNA cleavage reactions, to assess the extent of oxidative damage to DNA in vivo and to investigate the mechanism of DNA damage by ionizing radiation and chemical carcinogens.

Damage to the DNA bases in mammalian chromatin by hydrogen peroxide in the presence of ferric and cupric ions

Modification of DNA bases in mammalian chromatin upon treatment with hydrogen peroxide in the presence of ferric and cupric ions was studied. Ten DNA base products in mammalian chromatin were identified and quantitated by the use of gas chromatography-mass spectrometry with selected-ion monitoring after hydrolysis of chromatin and trimethylsilylation of hydrolysates. This technique permitted the analysis of modified DNA bases in chromatin without the necessity of isolation of DNA from chromatin first. Modified bases identified were typical hydroxyl radical-induced products of DNA, indicating the involvement of hydroxyl radical in their formation. This was also confirmed by inhibition of product formation by typical scavengers of hydroxyl radical. The inhibition of product formation was much more prominent in the presence of chelated ions than unchelated ions, indicating a possible site-specific formation of hydroxyl radical when metal ions are bound to chromatin. Hydrogen peroxide in the presence of cupric ions caused more DNA damage than in the presence of ferric ions. Chelation of cupric ions caused a marked inhibition in product formation. By contrast, DNA was damaged more extensively in the presence of chelated ferric ions than in the presence of unchelated ferric ions. The presence of ascorbic acid generally increased the yields of the products, indicating increased production of hydroxyl radical by reduction of metal ions by ascorbic acid. Superoxide dismutase afforded partial inhibition of product formation only in the case of chelated iron ions. The yields of the modified bases in chromatin were lower than those observed with calf thymus DNA under the same conditions.

Copper-ion-dependent damage to the bases in DNA in the presence of hydrogen peroxide

Mixtures of Cu2+ and H2O2 at pH 7.4 caused damage to the bases in DNA greater than that caused by mixtures of Fe3+ and H2O2. Addition of ascorbic acid to the Cu2+/H2O2 system caused a very large increase in base damage, much greater than that produced by the Fe3+/H2O2/ascorbic acid system. The products of base damage in the presence of Cu2+ were typical products that have been shown to result from attack of hydroxyl radicals upon the DNA bases. Cytosine glycol, thymine glycol, 8-hydroxyadenine and especially 8-hydroxyguanine were the major products in both the Cu2+/H2O2 and the Cu2+/H2O2/ascorbic acid systems. Base damage in DNA by these systems was inhibited by the chelating agents EDTA and nitrilotriacetic acid and by catalase, but not by superoxide dismutase, nor by the hydroxyl-radical scavenger mannitol. It is proposed that Cu2+ ions bound to the DNA react with H2O2 and ascorbic acid to generate hydroxyl radicals, which then immediately attack the DNA bases in a site-specific manner. A hypoxanthine/xanthine oxidase system also caused damage to the DNA bases in the presence of Cu2+ ions. This was inhibited by superoxide dismutase and catalase. The high activity of Cu2+ ions, when compared with Fe3- ions, in causing hydroxyl-radical-dependent damage to DNA and to other biomolecules, means that the availability of Cu2+ ions in vivo must be carefully controlled.

Preliminary study of the protective effect of the calcium channel blocker, nifedipine, on adriamycin-induced tissue injury

The effect of nifedipine, an oral calcium-channel blocker, on adriamycin-induced wound healing was studied. Nifedipine was administered to animals prior to treating with adriamycin. The healing strengths of cecal, fascial, and skin anatomoses were measured. Animals treated with adriamycin alone had significant decreases in healing strength compared to controls: for cecum at postoperative days (POD) 7 and 14; for skin at PODs 14, 21, and 28; for fascia at POD 28. Overall, nifedipine reduced the impact of adriamycin injury on the strength of healing incisional anastomoses. Nifedipine also appeared to protect collagen synthesis at anastomotic sites from adriamycin-induced impairment.

Chemical determination of free radical-induced damage to DNA

Free radical-induced damage to DNA in vivo can result in deleterious biological consequences such as the initiation and promotion of cancer. Chemical characterization and quantitation of such DNA damage is essential for an understanding of its biological consequences and cellular repair. Methodologies incorporating the technique of gas chromatography/mass spectrometry (GC/MS) have been developed in recent years for measurement of free radical-induced DNA damage. The use of GC/MS with selected-ion monitoring (SIM) facilitates unequivocal identification and quantitation of a large number of products of all four DNA bases produced in DNA by reactions with hydroxyl radical, hydrated electron, and H atom. Hydroxyl radical-induced DNA-protein cross-links in mammalian chromatin, and products of the sugar moiety in DNA are also unequivocally identified and quantitated. The sensitivity and selectivity of the GC/MS-SIM technique enables the measurement of DNA base products even in isolated mammalian chromatin without the necessity of first isolating DNA, and despite the presence of histones. Recent results reviewed in this article demonstrate the usefulness of the GC/MS technique for chemical determination of free radical-induced DNA damage in DNA as well as in mammalian chromatin under a vast variety of conditions of free radical production.

The enzymatic one-electron reduction of porphyrins to their anion free radicals

The anaerobic enzymatic one-electron reduction of uroporphyrin I (in the absence of light) by the ferredoxin/ferredoxin:NADP+ oxidoreductase system was investigated using NADPH as the source of reducing equivalents. The porphyrin anion free radical metabolite formed by one-electron reduction of the parent molecule was detected with ESR spectroscopy. The ESR spectrum exhibited a singlet (g = 2.0021) with a 5.4-G peak-to-peak linewidth. The reduction process was also investigated under aerobic conditions. The reduction of molecular oxygen to superoxide anion radical by the porphyrin anion radical was demonstrated by using the ESR technique of spin trapping. The ESR spectra of the spin-trapped oxygen-derived radicals were superoxide dismutase-sensitive and catalase-insensitive, supporting the assignment of the trapped radical to the superoxide anion radical. These aerobic experiments demonstrate electron transfer from the porphyrin anion radical to molecular oxygen. The anaerobic reduction of Photofrin II by hepatic microsomes and the ferredoxin/ferredoxin:NADP+ oxidoreductase system to a porphyrin anion radical was also investigated. Free radical formation by ferredoxin: NADP+ oxidoreductase is totally dependent upon ferredoxin. The ESR spectrum of this porphyrin free radical also exhibited a singlet (g = 2.0026) with a 15-G peak-to-peak linewidth.

The role of hydroxyl radicals in tetrachlorohydroquinone induced DNA strand break formation in PM2 DNA and human fibroblasts

Tetrachlorohydroquinone (TCHQ), which has previously been identified as a metabolite of pentachlorophenol, induces DNA strand breaks in isolated DNA and in human fibroblasts. Strand break formation in PM2 DNA is prevented by the addition of catalase and the hydroxyl radical scavengers DMSO, ethanol and mannitol, whereas addition of SOD reduced SSB only slightly. Oxygen radicals are formed by the autoxidation of TCHQ to the tetrachlorosemiquinone radical. Desferrioxamine (0.2 mM) completely abolished strand break formation, whereas the metal chelator DETAPAC (1 mM) reduced SSB by only 8.5%. The formation of the semiquinone radical at physiological conditions is shown by ESR spectroscopy. Exposure of human fibroblasts to TCHQ also leads to DNA single strand breaks measured by the alkaline elution assay. These were reduced by addition of 5% DMSO. This indicates that at least part of the strand break formation in human cells is also due to the action of hydroxyl radicals.

Doxorubicin (adriamycin): a critical review of free radical-dependent mechanisms of cytotoxicity

The antineoplastic drug doxorubicin is capable of generating a variety of free radical species in subcellular systems and this capacity has been considered critical for its antitumor action. However, for most tumor cell lines this mechanism of cytotoxicity does not appear to play a major role. Free radical-independent cytotoxicity mechanisms, taking place in the nuclear compartment of the cell, may more likely be involved in the antitumor effect of doxorubicin.

Effect of artificial electron acceptors on the cytotoxicity of mitomycin C and doxorubicin in human lung tumor cells

The cytotoxicities of mitomycin C (MMC) and doxorubicin (DOX) have been proposed to depend on intracellular reduction by reduced flavoproteins. We investigated whether MMC- and DOX-induced cytotoxicity could be inhibited by competing for electrons from reduced flavoproteins by the artificial electron acceptors phenazine methosulfate (PMS), menadione (MEN) and methylene blue (MB). In intact SW-1573 human lung tumor cells these compounds proved to be excellent electron acceptors, as judged from their capacity to induce high levels of cyanide-resistant respiration. In addition, PMS, MEN and MB were found to decrease the cytotoxicity of MMC, by 90, 63 and 29%, respectively, at concentrations that were themselves completely nontoxic. In contrast, DOX cytotoxicity was not detectably affected. These results suggest that in SW-1573 cells flavoprotein-mediated bioreduction is required for the cytotoxic effect of MMC, but not for that of DOX.

Evidence for three differentially regulated catalase genes in Neurospora crassa: effects of oxidative stress, heat shock, and development

Genetic and biochemical studies demonstrated that Neurospora crassa possesses three catalases encoded by three separate structural genes. The specific activities of the three enzymes varied in response to superoxide-mediated stress, heat shock, and development. The three loci, which we designated cat-1, cat-2, and cat-3, map to the right arms of chromosomes III, VII, and III, respectively. The cat-1-encoded enzyme (designated Cat-1; estimated molecular weight, 315,000; pI 5.2) was the predominant catalase in rapid-growth mycelium, and its activity was substantially increased in paraquat-treated and heat-shocked mycelium. Cat-2 (Mw, 165,000; pI 5.4) was absent from rapid-growth mycelium but present at low levels in conidia and stationary-phase mycelium. It was the predominant catalase in extracts derived from mycelium that had been heat shocked for 2 h. Cat-3 (Mw, 340,000; pI 5.5) was the predominant catalase in extracts from mature conidia.

Free radical formation by antitumor quinones

Quinones are among the most frequently used drugs to treat human cancer. All of the antitumor quinones can undergo reversible enzymatic reduction and oxidation, and form semiquinone and oxygen radicals. For several antitumor quinones enzymatic reduction also leads to formation of alkylating species but whether this involves reduction to the semiquinone or the hydroquinone is not always clear. The antitumor activity of quinones is frequently linked to DNA damage caused by alkylating species or oxygen radicals. Some other effects of the antitumor quinones, such as cardiotoxicity and skin toxicity, may also be related to oxygen radical formation. The evidence for a relationship between radical formation and the biological activity of the antitumor quinones is evaluated.

Recent advances in the development of a diagnostic test for irradiated foodstuffs

Recent advances in the development and application of diagnostic tests for irradiated foodstuffs are reviewed. Exposure of water, the major chemical constituent of most foodstuffs to a source of ionising radiation initially generates the highly reactive radical species H., .OH and e- (aq) which react very rapidly with a wide variety of biological molecules. The detection of foodstuffs subjected to irradiation processing requires the identification and/or quantification of 'unnatural' chemical species (i.e. those not usually formed by normal metabolic processes) produced by the attack of .OH radical or e- (aq) on suitable 'target' molecules. Modern methods for the analysis of a series of these 'unnatural' products arising from the interaction of radiolytically-generated .OH radical or e- (aq) with polyunsaturated fatty acids, DNA, aromatic compounds and other biologically important scavenger molecules are examined. It is concluded that the analytical test to be conducted is highly dependent on the nature of the foodstuff to be tested.

The role of hydroxyl radical in chromosomal and plasmid damage in Neisseria gonorrhoeae in vivo

Viable Neisseria gonorrhoeae exposed to streptonigrin generate intracellular hydroxyl radical detected by spin-trapping with 5,5-dimethyl-l-pyrroline-N-oxide; gonococci exposed to paraquat generate primarily superoxide (J. Biol. Chem., 262: 13404-143048, 1987). The use of streptonigrin and paraquat provide a model with which to examine the action and site(s) of hydroxyl radical-mediated damage. N. gonorrhoeae exposed to streptonigrin, but not paraquat, developed extensive chromosomal, plasmid, and RNA damage. Addition of excess Fe+3 to the reaction mixture enhanced intracellular hydroxyl radical formation by paraquat, detectable as DNA damage. Desferal and dimethyl sulfoxide allowed approximately 25% of protection of plasmid DNA damage as judged by linear scanning densitometry. These results demonstrate DNA and RNA damage in viable organisms exposed to intracellular redox stress and confirm the critical role of hydroxyl radical in this process.

gamma-radiolysis study of the reduction by COO- free radicals of daunorubicin intercalated in DNA

The reduction of daunorubicin intercalated in DNA was studied using COO- free radicals produced by gamma-radiolysis as reductants. The reduction process of the drug intercalated in DNA was found to be very similar to the one of daunorubicin in aqueous solution without DNA. (a) the final product is the same (7-deoxy daunomycinone); (b) the reduction yield is the same [2.6 +/- 0.2) x 10(-7) mol.J-1); (c) H2O2 reacts with hydroquinone daunorubicin giving back the drug in a one-step reaction. However 7-deoxy daunomycinone precipitation was so slow that this aglycone could be reduced by COO- free radicals giving its hydroquinone form, which cannot be observed without DNA. This shows that the whole 4-electron reduction process takes place in DNA. The implications of these findings are discussed.

Free radical production at the site of an acute inflammatory reaction as measured by chemiluminescence

A foot-pad oedema model was used to investigate the presence of free radicals using a chemiluminescence method. This model is an example of a cell mediated hypersensitivity reaction. Male rats were inoculated in the scruff with Freund's Complete Adjuvant (FCA) on Day 0 and then challenged 6 days later with FCA in one hind paw. An acute inflammatory reaction was initiated over the following 96 hours and within 4 hours of induction, reactive oxygen species were detected in the inflamed tissue. A peak of chemiluminescence activity was seen 8 hours after the induction of the inflammatory reaction, well before maximum oedema was observed. Using mannitol, catalase and DABCO to elucidate the nature of the reactive oxygen species it was found that hydroxyl radicals, hydrogen peroxide and singlet oxygen all contributed to this burst of oxidative activity and are therefore probably involved with the process of lipid peroxidation and the severity of an inflammatory reaction.

Cellular targets of adriamycin-induced damage in Escherichia coli

The cellular targets of adriamycin (ADR) activity were studied in Escherichia coli by following colony forming ability and various cellular functions. The parameter exhibiting the best correlation with mortality was inhibition of RNA synthesis. Total DNA synthesis was inhibited to a lesser extent, but may reflect a concurrent inhibition of replication and stimulation of DNA repair activity. Protein synthesis, membrane function and rate of oxygen consumption were affected later. No extensive DNA fragmentation was observed. The inhibition of RNA synthesis was independent of the stringent response and of inhibition of DNA synthesis induced by nalidixic acid. ADR activated the SOS repair system, and the lesions induced by the drug could be repaired by recA dependent functions. These results indicate that the primary activity of ADR was directed against the DNA and interfered with the DNA template function.

Release of iron from ferritin by cardiotoxic anthracycline antibiotics

The use of the extremely effective anthracycline antitumor drugs adriamycin and daunomycin is limited by a severe, dose-dependent cardiomyopathy. Anthracycline-induced toxicity has been proposed to involve iron-dependent oxidative damage to biological macromolecules yet little is known regarding the availability of physiologic iron. We now report that, in the presence of NADPH-cytochrome P-450 reductase, these drugs undergo redox cycling to generate superoxide which mediates a slow, reductive release of iron from ferritin, the major intracellular iron storage protein. Anaerobically, the semiquinone free radical forms of adriamycin and daunomycin catalyze a very rapid, extensive release of iron from ferritin. In contrast, diaziquone, an aziridinyl quinone antitumorigenic agent which is less cardiotoxic, is unable to release iron from ferritin. Thus, the present studies suggest that the cardiomyopathy observed with the anthracyclines, and perhaps their antineoplastic activity as well, may be related to their ability to delocalize tissue iron, thereby contributing to the formation of strong oxidants capable of damaging critical cellular constituents.

Redox activities of antitumor anthracyclines determined by microsomal oxygen consumption and assays for superoxide anion and hydroxyl radical generation

To explore the structural characteristics of various derivatives of the anticancer drugs, doxorubicin and daunorubicin, for exhibiting redox activities believed to be associated with toxic radical production, we tested over fifty derivatives in a rapid screening procedure for augmenting oxygen consumption by rat liver microsomes. Measurement of parent drug disappearance and of metabolite appearance for fourteen anthracyclines with a broad range of activities for augmenting oxygen consumption indicated that a single reaction, conversion to the 7-deoxyaglycone, occurred. Multiple tests of selected compounds showed that the liver microsome system exhibited saturation kinetics, and calculated values of Vmax/Km gave the same relative order of activities as did the screening test. The liver microsome system was not found to be stereoselective. Measurements of the abilities of a number of the anthracycline derivatives after chemical activation by reduction with sodium borohydride to convert oxygen to superoxide anion, or to the hydroxyl radical, were also made. The reactivities of the anthracyclines in these latter two assays were positively related to the activities obtained in the rat liver microsome screening test, suggesting that all three tests were measuring various steps in the sequence from anthracycline semiquinone radical formation through oxygen activation and radical formation. Superoxide anion generation from chemically reduced anthracyclines was inhibited by the addition of calf thymus DNA, and the extent of inhibition was positively correlated with the measured DNA association constants of the anthracyclines. However, the DNA association constants were unrelated to superoxide anion generation in the absence of DNA or to the augmentation of oxygen consumption in liver microsomes. Half-wave potentials were negatively correlated with both the results of the microsomal oxygen consumption test and the production of superoxide anion in the chemical test system. No relationships were discerned among the DNA association constants, half-wave potentials, or reoxidizabilities of the anthracyclines tested. Comparisons of the relatively low activities of certain of the anthracyclines in the biochemical and chemical tests for oxygen activation with their known high activities against murine tumors in vivo, but low cardiotoxicities in animal model systems, suggest that the separation of the cytotoxic antitumor and cardiotoxic actions of these derivatives may have been achieved.

Reduction of oxygen by NADH/NADH dehydrogenase in the presence of adriamycin

Cardiac mitochondrial NADH dehydrogenase (Cytochrome c reductase, EC1.6.99.3) catalyses the reduction of ferricytochrome c to ferrocytochrome c by NADH. In the presence of the anthracycline anti-tumour drug, adriamycin, electron transfer from NADH is subverted to dioxygen. Using the electron spin resonance technique of spin trapping with the spin trapping agent 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) adriamycin was found to stimulate the formation of superoxide and hydroxyl radicals in the NADH/NADH dehydrogenase reaction. Hydroxyl radical formation is dependent on the availability of trace amounts of redox active metal ions - particularly ferric ions. Trace amounts of ferric ions catalyse the formation of hydroxyl radicals by both superoxide-dependent and adriamycin-dependent one electron reduction of hydrogen peroxide. The metabolism of adriamycin by cardiac mitochondrial NADH dehydrogenase may be an important etiological factor in adriamycin-induced cardiotoxicity. It may be therapeutically beneficial to keep nonessential ferric/ferrous ions in the myocardium at minimum levels with siderophoric iron chelators - providing the anti-tumour activity of adriamycin is not impaired.

Non-enzymic lipid peroxidation in microsomes and microsomal phospholipids induced by anthracyclines

The stimulation of non-enzymic lipid peroxidation by doxorubicin, daunorubicin and 7 derivatives was investigated in extracted microsomal phospholipids and in intact microsomes. Evidence was obtained for the necessity of a free amino-sugar moiety for a stimulative effect on lipid peroxidation. Binding of anthracyclines to RNA (which is present in microsomes) was inhibitory towards stimulation. Drugs that stimulated lipid peroxidation in a non-enzymic system with extracted phospholipids also were stimulative in an enzymic, NADPH-dependent, microsomal system. They were not always effective in intact microsomes without the enzymic system. The role of the enzymic system in the stimulation of anthracycline induced lipid peroxidation is thought to be the reduction of iron ions rather than the stimulation of oxygen radical production via the anthracyclines.

Free radical damage to deoxyribose by anthracycline, aureolic acid and aminoquinone antitumour antibiotics. An essential requirement for iron, semiquinones and hydrogen peroxide

Anthracycline, aureolic acid and aminoquinone antitumour antibiotics damage deoxyribose in cell-free systems when reduced in air by the enzyme ferredoxin reductase. Damage to deoxyribose is inhibited by the iron chelator desferrioxamine, the copper-containing protein caeruloplasmin and catalase but not by superoxide dismutase. Scavengers of the hydroxyl radical such as formate, butan-1-ol, ethanol and benzoate do not offer much protection, whereas mannitol and thiourea do. These findings point to a site-specific Fenton reaction in which the drug semiquinones reduce complexed iron and dioxygen leading to the formation of hydrogen peroxide and a ferrous complex.