Cu(II)/H2O2-induced DNA damage is enhanced by packaging of DNA as a nucleosome

Copper-Based Complexes with Adamantane Ring-Conjugated bis(3,5-Dimethyl-pyrazol-1-yl)acetate Ligand as Promising Agents for the Treatment of Glioblastoma

The new ligand L2Ad, obtained by conjugating the bifunctional species bis(3,5-dimethylpyrazol-1-yl)-acetate and the drug amantadine, was used as a chelator for the synthesis of new Cu complexes 1-5. Their structures were investigated by synchrotron radiation-induced X-ray photoelectron spectroscopy (SR-XPS), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and by combining X-ray absorption fine structure (XAFS) spectroscopy techniques and DFT modeling. The structure of complex 3 was determined by single-crystal X-ray diffraction analysis. Tested on U87, T98, and U251 glioma cells, Cu(II) complex 3 and Cu(I) complex 5 decreased cell viability with IC50 values significantly lower than cisplatin, affecting cell growth, proliferation, and death. Their effects were prevented by treatment with the Cu chelator tetrathiomolybdate, suggesting the involvement of copper in their cytotoxic activity. Both complexes were able to increase ROS production, leading to DNA damage and death. Interestingly, nontoxic doses of 3 or 5 enhanced the chemosensitivity to Temozolomide.

Heavy metals toxicity on epigenetic modifications in the pathogenesis of Alzheimer's disease (AD)

Alzheimer's disease (AD) is a progressive decline in cognitive ability and behavior which eventually disrupts daily activities. AD has no cure and the progression rate varies unlikely. Among various causative factors, heavy metals are reported to be a significant hazard in AD pathogenesis. Metal-induced neurodegeneration has been focused globally with thorough research to unravel the mechanistic insights in AD. Recently, heavy metals suggested to play an important role in epigenetic alterations which might provide evidential results on AD pathology. Epigenetic modifications are known to play towards novel therapeutic approaches in treating AD. Though many studies focus on epigenetics and heavy metal implications in AD, there is a lack of research on heavy metal influence on epigenetic toxicity in neurological disorders. The current review aims to elucidate the plausible role of cadmium (Cd), iron (Fe), arsenic (As), copper (Cu), and lithium (Li) metals on epigenetic factors and the increase in amyloid beta and tau phosphorylation in AD. Also, the review discusses the common methods of heavy metal detection to implicate in AD pathogenesis. Hence, from this review, we can extend the need for future research on identifying the mechanistic behavior of heavy metals on epigenetic toxicity and to develop diagnostic and therapeutic markers in AD.

One step cascade detection of galactose based on a galactose oxidase-composited peroxidase nanozyme

Abnormal galactose metabolism is the main cause of galactosemia, which makes the accurate and rapid analysis of galactose levels in food and organism the key issue at present. In this study, a novel strategy for one-step galactose determination was proposed based on galactose oxidase and copper-based metal-organic framework complexes (GAOx@MOF) with dual catalytic activities at neutral pH. Typically, GAOx catalyzes the oxidation of the C6 hydroxyl group of D-galactose to generate an aldehyde (D-galactose-hexanedial), and coupled with the reduction of dioxygen to H₂O₂, which was immediately transformed to ˙OH by mimicking peroxidase activity and at the same time oxidized ABTS to a green product with a clear colorimetric signal. The whole process was completed using one buffer, which simplified the procedure and increased the sensitivity. Moreover, the proposed method can also be used for the quantitative analysis of galactose. It showed a good linear relationship at 20-1000 μM, while the LOD was 6.67 μM. Furthermore, the strategy has been successfully utilized for galactose determination in milk samples, which proved its promising applications in clinical analysis and the food industry.

Atom probe tomography and transmission electron microscopy: a powerful combination to characterize the speciation and distribution of Cu in organic matter

The large surface areas in porous organic matter (OM) and on the surface of altered minerals control the sequestration of metal(loid)s in contaminated soils and sediments. This study explores the sequestration of Cu by OM in surficial forest soil in close proximity to the Horne smelter, Rouyn-Noranda, Quebec, Canada. The organic-rich soils have elevated concentrations of Cu (Cu = 〈0.75〉 wt%) but lack associations between organic matter (OM) and Cu-sulfides, commonly observed in organic-rich Cu-contaminated soils. This provides a unique opportunity to study the sequestration of Cu by OM in a sulfur-depleted environment using a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atom probe tomography (APT). In two examined OM particles, Cu is predominantly sequestered as (I) nano- to micrometer-size Cu-bearing spinels, (II) as cuprite (Cu₂O) nanoparticles or (III) finely dispersed Cu in association with clusters of magnetite (Fe₃O₄) nanoparticles embedded in amorphous silica-rich pockets and (IV) in the OM matrix. The occurrence of euhedral crystals and nanoparticles in the single-digit range within the OM matrix indicate that the majority of the nanoparticles formed in situ within the OM particles. A model is developed which proposes that the sequestration of Cu in OM is promoted by (I) the partial mineralization of the OM matrix by amorphous silica; (II) the nucleation of magnetite nanoparticles on highly reactive silanol groups; (III) the diffusion of Cu within mineralized and altered areas of the OM; (IV) the availability of Cu-bearing species, which in turn is controlled by the hydrodynamic properties of the pore channels; (V) the formation of precursors and nucleation of Cu-bearing nanoparticles. This study shows that the combination of SEM, TEM and APT provides new insights into the sequestration of metal contaminants by OM at various scales ranging from the single-digit nano- to micrometer scale.

The role of organic colloids in the sequestration and mobilization of copper in smelter-impacted soils

This study shows that Cu occurs predominantly as Cu-sulfides and Cu-bearing phosphates and -carbonates in organic matter (OM) colloids within smelter-impacted soils in which they are often associated with other inorganic components. Major emitters of Cu are smelters and coal-power plants, which cause severe damage to the health of soils and aquatic systems as elevated Cu concentrations are toxic for terrestrial and aquatic organisms. Toxic effects and the long-term environmental fate of Cu depend among many other factors on its speciation in soil and water bodies. This study explores the role of OM colloids (defined as particles with diameters in the range of 100 to 1000 nm and with a larger proportion of organic than inorganic material) in the sequestration of Cu in contaminated soils around the Horne smelter, Rouyn Noranda, Quebec, Canada, focusing on a thin soil overlying bedrock (bedrock soil) and forest soil. The sequestration and mobilization of Cu by OM colloids are studied using a combination of column leaching experiments, ultra-centrifugation and transmission electron microscopy (TEM). TEM analysis indicates that Cu occurs as nano-sized CuS_x phases in OM colloids of the bedrock soil, and as Cu-bearing Ca-Mg-phosphates and Ca-carbonates in OM colloids of the forest soil. The nano-sized CuS_x phases occur along the rim of OM colloids or are attached to silica inclusions located within OM colloids, suggesting that their in situ formation is strongly controlled by the presence of polar groups within or on the surface of OM colloids. The proportion of Cu-bearing colloids in the soil leachates ranges from 20 to 40% of the total colloidal fraction, suggesting that OM colloids can play a significant role in the sequestration of Cu in surficial soil environments.

Mitochondrial DNA: Consensuses and Controversies

In the course of its short history, mitochondrial DNA (mtDNA) has made a long journey from obscurity to the forefront of research on major biological processes. mtDNA alterations have been found in all major disease groups, and their significance remains the subject of intense research. Despite remarkable progress, our understanding of the major aspects of mtDNA biology, such as its replication, damage, repair, transcription, maintenance, etc., is frustratingly limited. The path to better understanding mtDNA and its role in cells, however, remains torturous and not without errors, which sometimes leave a long trail of controversy behind them. This review aims to provide a brief summary of our current knowledge of mtDNA and highlight some of the controversies that require attention from the mitochondrial research community.

Discovery of the Involvement in DNA Oxidative Damage of Human Sperm Nuclear Basic Proteins of Healthy Young Men Living in Polluted Areas

DNA oxidative damage is one of the main concerns being implicated in severe cell alterations, promoting different types of human disorders and diseases. For their characteristics, male gametes are the most sensitive cells to the accumulation of damaged DNA. We have recently reported the relevance of arginine residues in the Cu(II)-induced DNA breakage of sperm H1 histones. In this work, we have extended our previous findings investigating the involvement of human sperm nuclear basic proteins on DNA oxidative damage in healthy males presenting copper and chromium excess in their semen. We found in 84% of those males an altered protamines/histones ratio and a different DNA binding mode even for those presenting a canonical protamines/histones ratio. Furthermore, all the sperm nuclear basic proteins from these samples that resulted were involved in DNA oxidative damage, supporting the idea that these proteins could promote the Fenton reaction in DNA proximity by increasing the availability of these metals near the binding surface of DNA. In conclusion, our study reveals a new and unexpected behavior of human sperm nuclear basic proteins in oxidative DNA damage, providing new insights for understanding the mechanisms related to processes in which oxidative DNA damage is implicated.

Copper and cadmium administration induce toxicity and oxidative stress in the marine flatworm Macrostomum lignano

The contamination of coastal regions with different toxicants, including heavy metal ions such as copper and cadmium jeopardize health and survival of organisms exposed to this habitat. To study the effects of high copper and cadmium concentrations in these marine environments, we used the flatworm Macrostomum lignano as a model. This platyhelminth lives in shallow coastal water and is exposed to high concentrations of all toxicants that accumulate in these sea floors. We could show that both, cadmium and copper show toxicity at higher concentrations, with copper being more toxic than cadmium. At concentrations below acute toxicity, a reduced long-term survival was observed for both metal ions. The effects of sublethal doses comprise reduced physical activities, an increase in ROS levels within the worms, and alterations of the mitochondrial biology. Moreover, cell death events were substantially increased in response to sublethal concentrations of both metal ions and stem cell activity was reduced following exposure to higher cadmium concentrations. Finally, the expression of several genes involved in xenobiotic metabolism was substantially altered by this intervention. Taken together, M. lignano has been identified as a suitable model for marine toxicological studies as it allows to quantify several relevant life-history traits as well as of physiological and behavioral read-outs.

One-step cascade detection of glucose at neutral pH based on oxidase-integrated copper(ii) metal–organic framework composites

An integrated system was fabricated from a copper(ii) metal–organic framework (Cu-MOF) and glucose oxidase (GOx) for one-step cascade determination of glucose at neutral pH (pH = 7.0).

Copper(II) generates ROS and RNS, impairs antioxidant system and damages membrane and DNA in human blood cells

Copper (Cu) is widely used in various industries, and human exposure to this metal results in severe multi-organ toxicity, which is thought to be due to the generation of free radicals by Fenton-like reaction. The generation of reactive oxygen as well as nitrogen species and free radicals results in induction of oxidative stress in the cell. We have studied the effect of different concentrations of Cu(II) on human erythrocytes and lymphocytes. Incubation of erythrocytes with copper chloride, a Cu(II) compound, enhanced the production of reactive oxygen and nitrogen species, decreased glutathione and total sulphydryl content and increased protein oxidation and lipid peroxidation. All changes were in a Cu(II) concentration-dependent manner. This strongly suggests that Cu(II) causes oxidative damage in erythrocytes. The activities of major antioxidant enzymes were altered, and antioxidant power was lowered. Cu(II) treatment also resulted in membrane damage in erythrocytes as seen by electron microscopy and lowered activities of plasma membrane-bound enzymes. Incubation of human lymphocytes with Cu(II) resulted in DNA damage when studied by the sensitive comet assay. These results show that Cu(II) exerts cytotoxic and genotoxic effects on human blood cells probably by enhancing the generation of reactive oxygen and nitrogen species.

Is mitochondrial DNA profiling predictive for athletic performance?

Mitochondrial DNA encodes some proteins of the oxidative phosphorylation enzymatic complex, playing an important role in aerobic ATP production; therefore, it can contribute to the ability to respond to endurance exercise training. The accumulation of mitochondrial mutations and the migratory processes of populations have given a great contribution to the development of haplogroups with a different distribution in the world. Several studies have shown the important role of gene polymorphisms in aerobic performance. In this review, some mitochondrial haplogroups and multiple rare alleles were taken into consideration and could be linked to the athlete's physical performance of different ethnic groups.

Integrated Antibody with Catalytic Metal-Organic Framework for Colorimetric Immunoassay

Enzyme-linked immunosorbent assay has been widely used as a gold standard in biomedical field, but some inevitable drawbacks still exist in its practical applications, especially the laborious preparation of enzyme-antibody conjugates by a covalent linkage. In this work, we proposed a new strategy to prepare enzyme-antibody conjugate by integrating antibody with catalytic metal-organic framework (MOF) to form dual-functional MOF/antibody composite. As models, rabbit antimouse immunoglobulin G antibody (RIgG) and Cu-MOF with peroxidase-like activity were used to fabricate RIgG@Cu-MOF composite for colorimetric immunoassay. It was found that Cu-MOF as a host not only has no influence on the original capture ability of RIgG to its corresponding antigen (mIgG), but also can shield RIgG against long-term storage, high temperature, and biological degradation. More importantly, upon the formation of sandwiched immunocomplex between RIgG@Cu-MOF and capture antibody, Cu-MOF can serve as a signal amplification unit to perform colorimetric immunoassay. The detection limit of RIgG@Cu-MOF toward mIgG was obtained at 0.34 ng/mL, which is 3-fold lower than that of horseradish peroxidase labeled RIgG. Furthermore, the successful determination of mIgG in serum sample demonstrates the applicability of RIgG@Cu-MOF in detecting real sample. Therefore, it is highly anticipated that this study can offer a new way to prepare enzyme-antibody conjugates, facilitating the exploration of MOF composites in biomedical field.

Relevance of arginine residues in Cu(II)-induced DNA breakage and Proteinase K resistance of H1 histones

This work analyzes the involvement of arginines in copper/H₂O₂-induced DNA breakage. Copper is a highly redox active metal which has been demonstrated to form compounds with arginines. For this aim we used mixtures of pGEM3 DNA plasmid and two types of H1 histones which differ only in their arginine content. The sperm H1 histone from the annelid worm Chaetopterus variopedatus (arginine content 12.6 mol% K/R ratio 2) and the somatic H1 histone from calf thymus (arginine content 1.8 mol% and K/R ratio 15). Copper/H₂O₂-induced DNA breakage was observed only in presence of sperm H1 histones, but it was more relevant for the native molecule than for the deguanidinated derivative (K/R ratio 14), in which 80% of arginine residues were converted to ornithine. Further, copper induced proteinase K resistance and increase of DNA binding affinity on native sperm H1 histones. These observations are consistent with a copper induced reorganization of the side-chains of arginine residues. Copper, instead, did not affect DNA binding affinity of somatic and deguanidinated H1 histones, which show similar K/R ratio and DNA binding mode. These results indicate that arginine residues could affect these H1 histones properties and provide new insights into copper toxicity mechanisms.

Formation and processing of DNA damage substrates for the hNEIL enzymes

Reactive oxygen species (ROS) are harnessed by the cell for signaling at the same time as being detrimental to cellular components such as DNA. The genome and transcriptome contain instructions that can alter cellular processes when oxidized. The guanine (G) heterocycle in the nucleotide pool, DNA, or RNA is the base most prone to oxidation. The oxidatively-derived products of G consistently observed in high yields from hydroxyl radical, carbonate radical, or singlet oxygen oxidations under conditions modeling the cellular reducing environment are discussed. The major G base oxidation products are 8-oxo-7,8-dihydroguanine (OG), 5-carboxamido-5-formamido-2-iminohydantoin (2Ih), spiroiminodihydantoin (Sp), and 5-guanidinohydantoin (Gh). The yields of these products show dependency on the oxidant and the reaction context that includes nucleoside, single-stranded DNA (ssDNA), double-stranded DNA (dsDNA), and G-quadruplex DNA (G4-DNA) structures. Upon formation of these products in cells, they are recognized by the DNA glycosylases in the base excision repair (BER) pathway. This review focuses on initiation of BER by the mammalian Nei-like1-3 (NEIL1-3) glycosylases for removal of 2Ih, Sp, and Gh. The unique ability of the human NEILs to initiate removal of the hydantoins in ssDNA, bulge-DNA, bubble-DNA, dsDNA, and G4-DNA is outlined. Additionally, when Gh exists in a G4 DNA found in a gene promoter, NEIL-mediated repair is modulated by the plasticity of the G4-DNA structure provided by additional G-runs flanking the sequence. On the basis of these observations and cellular studies from the literature, the interplay between DNA oxidation and BER to alter gene expression is discussed.

Synthesis and characterization of steroidal heterocyclic compounds, DNA condensation and molecular docking studies and their in vitro anticancer and acetylcholinesterase inhibition activities

A facile and efficient approach for the synthesis of steroidal heterocyclic compounds (4–12) has been performed. Furthermore, these newly synthesized compounds were evaluated for their various biological activities.

Copper: toxicological relevance and mechanisms

Copper (Cu) is a vital mineral essential for many biological processes. The vast majority of all Cu in healthy humans is associated with enzyme prosthetic groups or bound to proteins. Cu homeostasis is tightly regulated through a complex system of Cu transporters and chaperone proteins. Excess or toxicity of Cu, which is associated with the pathogenesis of hepatic disorder, neurodegenerative changes and other disease conditions, can occur when Cu homeostasis is disrupted. The capacity to initiate oxidative damage is most commonly attributed to Cu-induced cellular toxicity. Recently, altered cellular events, including lipid metabolism, gene expression, alpha-synuclein aggregation, activation of acidic sphingomyelinase and release of ceramide, and temporal and spatial distribution of Cu in hepatocytes, as well as Cu-protein interaction in the nerve system, have been suggested to play a role in Cu toxicity. However, whether these changes are independent of, or secondary to, an altered cellular redox state of Cu remain to be elucidated.

The "fast" and the "slow" modes of mitochondrial DNA degradation

In a living cell, oxidative stress resulting from an external or internal insult can result in mitochondrial DNA (mtDNA) damage and degradation. Here, we show that in HeLa cells, mtDNA can withstand relatively high levels of extracellular oxidant H2O2 before it is damaged to a point of degradation, and that mtDNA levels in these cells quickly recover after removal of the stressor. In contrast, mtDNA degradation in mouse fibroblast cells is induced at eight-fold lower concentrations of H2O2, and restoration of the lost mtDNA proceeds much slower. Importantly, mtDNA levels in HeLa cells continue to decline even after withdrawal of the stressor thus marking the "slow" mode of mtDNA degradation. Conversely, in mouse fibroblasts maximal loss of mtDNA is achieved during treatment, and is already detectable at 5 min after exposure, indicating the "fast" mode. These differences may modulate susceptibility to oxidative stress of those organs, which consist of multiple cell types.

Mechanisms of base substitution mutagenesis in cancer genomes

Cancer genome sequence data provide an invaluable resource for inferring the key mechanisms by which mutations arise in cancer cells, favoring their survival, proliferation and invasiveness. Here we examine recent advances in understanding the molecular mechanisms responsible for the predominant type of genetic alteration found in cancer cells, somatic single base substitutions (SBSs). Cytosine methylation, demethylation and deamination, charge transfer reactions in DNA, DNA replication timing, chromatin status and altered DNA proofreading activities are all now known to contribute to the mechanisms leading to base substitution mutagenesis. We review current hypotheses as to the major processes that give rise to SBSs and evaluate their relative relevance in the light of knowledge acquired from cancer genome sequencing projects and the study of base modifications, DNA repair and lesion bypass. Although gene expression data on APOBEC3B enzymes provide support for a role in cancer mutagenesis through U:G mismatch intermediates, the enzyme preference for single-stranded DNA may limit its activity genome-wide. For SBSs at both CG:CG and YC:GR sites, we outline evidence for a prominent role of damage by charge transfer reactions that follow interactions of the DNA with reactive oxygen species (ROS) and other endogenous or exogenous electron-abstracting molecules.

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.

Oxidative DNA adducts detected in vitro from redox activity of cigarette smoke constituents

Cigarette smoke contains a variety of carcinogens, cocarcinogens, mutagens, and tumor promoters. In addition to polycyclic aromatic carcinogens and tobacco-specific nitrosamines, cigarette smoke also contains an abundance of catechols, aldehydes, and other constituents, which are DNA damaging directly or indirectly; therefore, they can also contribute to cigarette smoke-mediated carcinogenicity. In this study, we investigated the potential of cigarette smoke constituents to induce oxidative damage to DNA through their capacity to redox cycle. When DNA (300 μg/mL) was incubated with cigarette smoke condensate (0.2 mg of tobacco particulate matter/mL) and CuCl(2) as a catalyst (50-100 μM), a variety of oxidative DNA adducts were detected by (32)P-postlabeling/TLC. Of the total adduct burden (2114 ± 419 adducts/10(6) nucleotides), over 40% of all adducts were attributed to the benchmark oxidative DNA lesion, 8-oxodeoxyguanosine (8-oxodG). Adducts were formed dose dependently. Essentially, similar adduct profiles were obtained when cigarette smoke condensate was substituted with ortho- and para-dihydroxybenzenes. Vehicle treatment with Cu(2+) or CSC alone did not induce any significant amount of oxidative DNA damage. Furthermore, coincubation of cigarette smoke condensate and ortho-dihydroxybenzene with DNA resulted in a higher amount of oxidative DNA adducts than obtained with the individual entity, suggesting that adducts presumably originated from catechols or catechol-like compounds in cigarette smoke condensate. Adducts resulting from both cigarette smoke condensate and pure dihydroxybenzenes were chromatographically identical to adducts formed by reaction of DNA with H(2)O(2), which is known to produce 8-oxodG, and many other oxidative DNA adducts. When the cigarette smoke condensate-DNA reaction was performed in the presence of ellagic acid, a known antioxidant, the adduct formation was inhibited dose dependently, further suggesting that adducts originated from oxidative pathway. Our data thus provide evidence of the capacity of catechols or catechol-like constituents in cigarette smoke to produce oxidative DNA damage, which may contribute to the tumor-promoting activity of cigarette smoke.

Fluorescence signaling of Zr4+ by hydrogen peroxide assisted selective desulfurization of thioamide

Thioamide derivative with a pyrene fluorophore was smoothly transformed to its corresponding amide by Zr(4+) ions in the presence of hydrogen peroxide. The transformation was evidenced by (1)H NMR spectroscopy and the signaling was completed within 10 min after sample preparation. Interference from Ag(+) and Hg(2+) ions in Zr(4+)-selective fluorescence signaling was readily suppressed with the use of Sn(2+) as a reducing additive. Discrimination of Zr(4+) from closely related hafnium, which is a frequent contaminant in commercial zirconium, was not possible. Prominent Zr(4+)-selective turn-on type fluorescence signaling was possible with a detection limit of 4.6 × 10(-6) M in an aqueous 99% ethanol solution.

DNA strand breakage induced by CuII and NiII, in the presence of peptide models of histone H2B

In the present study we used the plasmid relaxation assay, a very sensitive method for detection of DNA strand breaks in vitro, in order to evaluate the role of peptide fragments of histone H2B in DNA strand breakage induced by copper and nickel. We have found that in the presence of peptides modeling the histone fold domain (H2B(32-62) and H2B(63-93)) as well as the N-terminal tail (H2B(1-31)) of histone H2B there is an increased DNA damage by Cu(2+)/H(2)O(2) and Ni(2+)/H(2)O(2) reaction mixtures. On the contrary, the C-terminal tail (H2B(94-125)) seems to have a protective role on the attack of ROS species to DNA. We have rendered our findings to the interactions of the peptides with DNA, as well as with the metal.

Characterization of 2'-deoxyguanosine oxidation products observed in the Fenton-like system Cu(II)/H2O2/reductant in nucleoside and oligodeoxynucleotide contexts

Reactive oxygen species attack both base and sugar moieties in DNA with a preference among the bases for reaction at guanine. In the present study, 2'-deoxyguanosine (dG) was oxidized by a copper-mediated Fenton reaction with the reductants ascorbate or N-acetyl-cysteine, yielding oxidation on both the base and the sugar. The primary oxidized lesions observed in these studies include the 2'-deoxyribonucleosides of 8-oxo-7,8-dihydroguanosine (dOG), spiroiminodihydantoin (dSp), guanidinohydantoin (dGh), oxazolone (dZ), and 5-carboxamido-5-formamido-2-iminohydantoin (d2Ih), as well as the free base guanine. d2Ih was the major product observed in the nucleoside, single- and double-stranded oligodeoxynucleotide contexts and is proposed to arise from oxidation at C5 of guanine. Product distribution studies provide insight into the role of the reductant in partitioning of dG base oxidation along the C5 and C8 pathways.

Antioxidant and prooxidant effects of polyphenol compounds on copper-mediated DNA damage

Inhibition of copper-mediated DNA damage has been determined for several polyphenol compounds. The 50% inhibition concentration values (IC(50)) for most of the tested polyphenols are between 8 and 480 μM for copper-mediated DNA damage prevention. Although most tested polyphenols were antioxidants under these conditions, they generally inhibited Cu(I)-mediated DNA damage less effectively than Fe(II)-mediated damage, and some polyphenols also displayed prooxidant activity. Because semiquinone radicals and hydroxyl radical adducts were detected by EPR spectroscopy in solutions of polyphenols, Cu(I), and H(2)O(2), it is likely that weak polyphenol-Cu(I) interactions permit a redox-cycling mechanism, whereby the necessary reactants to cause DNA damage (Cu(I), H(2)O(2), and reducing agents) are regenerated. The polyphenol compounds that prevent copper-mediated DNA damage likely follow a radical scavenging pathway as determined by EPR spectroscopy.

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.

Oxidative DNA adducts after Cu(2+)-mediated activation of dihydroxy PCBs: role of reactive oxygen species

Polychlorinated biphenyls (PCBs) are toxic industrial chemicals, complete carcinogens, and efficacious tumor promoters. However, the mechanism(s) of PCB-mediated carcinogenicity remains largely undefined. One likely pathway by which these agents may play a role in carcinogenesis is the generation of oxidative DNA damage by redox cycling of dihydroxylated PCB metabolites. We have now employed a new (32)P-postlabeling system to examine novel oxidative DNA lesions induced by Cu(2+)-mediated activation of PCB metabolites. (32)P postlabeling of DNA incubated with various PCB metabolites resulted in over a dozen novel polar oxidative DNA adducts that were chromatographically similar for all active agents. The most potent metabolites tested were the hydroquinones (hydroxyl groups arranged para to each other), yielding polar oxidative adduct levels ranging from 55 to 142 adducts/10(6) nucleotides. PCB catechols, or ortho-dihydroxy metabolites, were up to 40% less active than their corresponding hydroquinone congeners, whereas monohydroxylated and quinone metabolites did not produce detectable oxidative damage over that of vehicle. With the exception of 2,4,5-Cl-2',5'-dihydroxybiphenyl, this oxidative DNA damage seemed to be inversely related to chlorine content: no chlorine approximately mono->di->trichlorinated metabolites. Importantly, copper, but not iron, was essential for activation of the PCB metabolites to these polar oxidative DNA adducts, because in its absence or in the presence of the Cu(+)-specific scavenger bathocuproine, no adducts were detected. Intervention studies with known reactive oxygen species (ROS) modifiers suggested that H(2)O(2), singlet oxygen, hydroxyl radical, and superoxide may also be involved in this PCB-mediated oxidative DNA damage. These data indicate a mechanistic role for several ROS, in addition to copper, in PCB-induced DNA damage and provide further support for oxidative DNA damage in PCB-mediated carcinogenesis.

Damage to cellular and isolated DNA induced by a metabolite of aspirin

Aspirin has been proposed as a possible chemopreventive agent. On the other hand, a recent cohort study showed that aspirin may increase the risk for pancreatic cancer. To clarify whether aspirin is potentially carcinogenic, we investigated the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), which is correlated with the incidence of cancer, in cultured cells treated with 2,3-dihydroxybenzoic acid (2,3-DHBA), a metabolite of aspirin. 2,3-DHBA induced 8-oxodG formation in the PANC-1 human pancreatic cancer cell line. 2,3-DHBA-induced DNA single-strand breaks were also revealed by comet assay using PANC-1 cells. Flow cytometric analyses showed that 2,3-DHBA increased the levels of intracellular reactive oxygen species (ROS) in PANC-1 cells. The 8-oxodG formation and ROS generation were also observed in the HL-60 leukemia cell line, but not in the hydrogen peroxide (H(2)O(2))-resistant clone HP100 cells, suggesting the involvement of H(2)O(2). In addition, an hprt mutation assay supported the mutagenicity of 2,3-DHBA. We investigated the mechanism underlying the 2,3-DHBA-induced DNA damage using (32)P-labeled DNA fragments of human tumor suppressor genes. 2,3-DHBA induced DNA damage in the presence of Cu(II) and NADH. DNA damage induced by 2,3-DHBA was enhanced by the addition of histone peptide-6 [AKRHRK]. Interestingly, 2,3-DHBA and histone peptide-6 caused base damage in the 5'-ACG-3' and 5'-CCG-3' sequences, hotspots of the p53 gene. Bathocuproine, a Cu(I) chelator, and catalase inhibited the DNA damage. Typical hydroxyl radical scavengers did not inhibit the DNA damage. These results suggest that ROS derived from the reaction of H(2)O(2) with Cu(I) participate in the DNA damage. In conclusion, 2,3-DHBA induces oxidative DNA damage and mutations, which may result in carcinogenesis.

Copper-catalyzed one-pot synthesis of benzimidazole derivatives

A simple, efficient, and environmentally benign method has been developed for the synthesis of 2-substituted benzimidazoles through a one-pot reaction of phenylenediamines with aryl aldehydes in excellent isolated yields under mild conditions using Cu(II) complex as the selective, recyclable, and heterogeneous catalyst at ambient temperature. The Cu(II) complex as a heterogeneous catalyst can be reused in further catalytic reactions, and it was found that its activity remained largely unchanged for eight successive runs. No metal-complex leaching was observed after the consecutive catalytic reactions. The salient features of this method include mild conditions, high yields, simple procedure, and good recovery and reusability of the heterogeneous catalyst.Key words: benzimidazole, o-phenylenediamine, arylaldehydes, heterogeneous catalyst, N,N-bis (2-hydroxyphenyl)pyridine-2,6-dicarboxamide.

Initiation of base excision repair of oxidative lesions in nucleosomes by the human, bifunctional DNA glycosylase NTH1

Oxidative lesions account for much of the spontaneously occurring DNA damage in normal cells and, left unrepaired, can be mutagenic or cytotoxic. We have investigated the capacity of purified human enzymes to initiate the base excision repair (BER) of oxidative lesions in model nucleosomes. In a construct where the minor groove of a thymine glycol lesion faced outward from the histone octamer, the human DNA glycosylase NTH1 (hNTH1) processed the lesion with nearly the same efficiency as in naked DNA. The hNTH1 reaction did not generate free DNA, indicating that the first step in BER occurred without irreversibly disrupting nucleosomes. Instead, lesion processing entailed the formation of nucleosome-hNTH1 ternary complexes that could be visualized in a gel mobility shift assay. These complexes contained both processed and unprocessed DNA. hNTH1 processing of lesions whose minor groove faced toward the histone octamer was poor at low hNTH1 concentrations but increased substantially as hNTH1 concentrations increased to nearly physiological levels. Additionally, an inward-facing lesion near the nucleosome edge was more efficiently processed than one closer to the nucleosome dyad. These observations suggest that access to sterically occluded lesions entails the partial, reversible unwrapping of DNA from the histone octamer, allowing hNTH1 to capture its DNA substrate when it is in an unwound state.

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

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

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

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

Radical production and DNA damage induced by carcinogenic 4-hydrazinobenzoic acid, an ingredient of mushroom Agaricus bisporus

4-Hydrazinobenzoic acid, an ingredient of mushroom Agaricus bisporus, is carcinogenic to rodents. To clarify the mechanism of carcinogenesis, we investigated DNA damage by 4-hydrazinobenzoic acid using (32)P-labeled DNA fragments obtained from the human p53 and p16 tumor suppressor genes. 4-Hydrazinobenzoic acid induced Cu(II)-dependent DNA damage especially piperidine-labile formation at thymine and cytosine residues. Typical hydroxyl radical scavengers showed no inhibitory effects on Cu(II)-mediated DNA damage by 4-hydrazinobenzoic acid. Bathocuproine and catalase inhibited the DNA damage, indicating the participation of Cu(I) and H(2)O(2) in the DNA damage. These findings suggest that H(2)O(2) generated by the autoxidation of 4-hydrazinobenzoic acid reacts with Cu(I) to form reactive oxygen species, capable of causing DNA damage. Interestingly, catalase did not completely inhibit DNA damage caused by a high concentration of 4-hydrazinobenzoic acid (over 50 microM) in the presence of Cu(II). 4-Hydrazinobenzoic acid induced piperidine-labile sites frequently at adenine and guanine residues in the presence of catalase. 4-Hydrazinobenzoic acid increased formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a characteristic oxidative DNA lesion, in calf thymus DNA, whereas 4-hydrazinobenzoic acid did not increase the formation of 8-oxodG in the presence of catalase. ESR spin-trapping experiments showed that the phenyl radical was formed during the reaction of 4-hydrazinobenzoic acid in the presence of Cu(II) and catalase. Matrix-assisted laser desorption/ionization time-of-flight mass (MALDI-TOF/mass) spectrometry analysis showed that phenyl radical formed adduct with adenosine and guanosine. These results suggested that 4-hydrazinobenzoic acid induced DNA damage via not only H(2)O(2) production but also phenyl radical production. This study suggests that both oxidative DNA damage and DNA adduct formation play important roles in the expression of carcinogenesis of 4-hydrazinobenzoic acid.

A novel naturally occurring tripyrrole with potential nuclease and anti-tumour properties

The DNA targeting and membrane damaging activities of a novel tripyrrole 1 obtained as a red pigment from the Micrococcus sp. were investigated. It was found that compound 1 binds with DNA efficiently and facilitates copper-mediated DNA cleavage as well as peroxidation of membrane lipids by a process that does not require any external reducing agent. Compound 1 also showed impressive cytotoxicity to both mouse and human tumour cell lines. The membrane damaging ability of compound 1 might be vital in its nuclease and cytotoxicity properties. Interestingly, compared to the various DNA cleaving agents, compound 1 showed a preferential binding with the G-C rich domain.

DNA Oxidation in Anionic Reverse Micelles: Ruthenium-Mediated Damage at Guanine in Single- and Double-Stranded DNA

One-electron guanine oxidation in DNA has been investigated in anionic reverse micelles (RMs). A photochemical method for generating Ru3+ from the ruthenium polypyridyl complex tris(2-2'-bipyridine)ruthenium(II) chloride ([Ru(bpy)3]Cl2) is combined with high-resolution polyacrylamide gel electrophoresis (PAGE) to quantify piperidine-labile guanine oxidation products. As characterized by emission spectroscopy of Ru(bpy)3(2+), the addition of DNA to RMs containing Ru(bpy)3(2+) does not perturb the environment of Ru(bpy)3(2+). The steady-state quenching efficiency of Ru(bpy)3(2+) with K3[Fe(CN)6] in buffer solution is approximately 2-fold higher than that observed in RMs. Consistent with the difference in quenching efficiency in the two media, a 1.5-fold higher yield of piperidine-labile damage products as monitored by PAGE is observed for duplex oligonucleotide in buffer vs RMs. In contrast, a 13-fold difference in the yield of PAGE-detected G oxidation products is observed when single-stranded DNA is the substrate. Circular dichroism spectra showed that single-stranded DNA undergoes a structural change in anionic RMs. This structural change is potentially due to cation-mediated adsorption of the DNA phosphates on the anionic headgroups of the RMs, leading to protection of the guanine from oxidatively generated damage.