DNA damage and cancer: measurement and mechanism

Structural and Dynamic Features of the Recognition of 8-oxoguanosine Paired with an 8-oxoG-clamp by Human 8-oxoguanine-DNA Glycosylase

8-oxoguanine (oxoG) is formed in DNA by the action of reactive oxygen species. As a highly mutagenic and the most common oxidative DNA lesion, it is an important marker of oxidative stress. Human 8-oxoguanine-DNA glycosylase (OGG1) is responsible for its prompt removal in human cells. OGG1 is a bifunctional DNA glycosylase with N-glycosylase and AP lyase activities. Aspects of the detailed mechanism underlying the recognition of 8-oxoguanine among numerous intact bases and its subsequent interaction with the enzyme's active site amino acid residues are still debated. The main objective of our work was to determine the effect (structural and thermodynamic) of introducing an oxoG-clamp in model DNA substrates on the process of 8-oxoG excision by OGG1. Towards that end, we used DNA duplexes modeling OGG1-specific lesions: 8-oxoguanine or an apurinic/apyrimidinic site with either cytidine or the oxoG-clamp in the complementary strand opposite to the lesion. It was revealed that there was neither hydrolysis of the N-glycosidic bond at oxoG nor cleavage of the sugar-phosphate backbone during the reaction between OGG1 and oxoG-clamp-containing duplexes. Possible structural reasons for the absence of OGG1 enzymatic activity were studied via the stopped-flow kinetic approach and molecular dynamics simulations. The base opposite the damage was found to have a critical effect on the formation of the enzyme-substrate complex and the initiation of DNA cleavage. The oxoG-clamp residue prevented the eversion of the oxoG base into the OGG1 active site pocket and impeded the correct convergence of the apurinic/apyrimidinic site of DNA and the attacking nucleophilic group of the enzyme. An obtained three-dimensional model of the OGG1 complex with DNA containing the oxoG-clamp, together with kinetic data, allowed us to clarify the role of the contact of amino acid residues with DNA in the formation of (and rearrangements in) the enzyme-substrate complex.

The Bioactive Compound Contents and Potential Protective Effects of Royal Jelly Protein Hydrolysates against DNA Oxidative Damage and LDL Oxidation

In this study, the inhibition of DNA oxidative damage and low-density lipoprotein (LDL) oxidation of royal jelly protein (RJP) hydrolysates obtained from two commercial proteases were investigated. The results showed that the inhibition of DNA oxidative damage induced by the Fenton reaction, RJP, RJPs hydrolyzed by alcalase (RJP-A), RJPs hydrolyzed by flavourzyme (RPJ-F) and RJP two-stage hydrolysates (RPJ-AF) all had the effect of inhibiting deoxyribose oxidative damage. The inhibition effect of RJP, RJP-A, RJP-F and RJP-AF (1.0 mg/mL) were 47.06%, 33.70%, 24.19% and 43.09%, respectively. In addition, studies have also found that both RJP and RJP hydrolysates can reduce the production of 8-OH-2'-dG and the order of its inhibitory ability is RJP-AF ≒ RJP-A > RJP-F > RJP. The inhibition of DNA damage induced by bleomycin-Fe³⁺/ascorbic acid (Asc) with the addition of RJP, RJP-A, RPJ-F and RPJ-AF were 17.16%, 30.88%, 25.00% and 37.25%, respectively. The results of LDL oxidation inhibition showed that RJP-AF (1 mg/mL) not only had the most effective inhibitory Cu²⁺-induced LDL oxidation to produce a thiobarbituric acid reactive substance (TBARS) but also extended the lag time of conjugated diene formation to 300 min, which was 3.3 times that of the control group.

Reactive oxygen species induce Cys106-mediated anti-parallel HMGB1 dimerization that protects against DNA damage

Oxidative stress can induce covalent disulfide bond formation between protein-protein thiol groups and generate hydroxyl free radicals that damage DNA. HMGB1 is a DNA chaperone and damage-associated molecular pattern molecule. As a redox-sensitive protein, HMGB1 contains three cysteine residues: Cys23, Cys45, and Cys106. In this study, we focused on the relationship between HMGB1 dimerization and DNA stabilization under oxidative stress conditions. HMGB1 dimerization was positively modulated by CuCl₂ and H₂O₂. Mutation of the Cys106 residue blocked dimer formation. Treatment of HEK293T cells with CuCl₂ and H₂O₂ enhanced the oxidative self-dimerization of HMGB1, whereas this dimerization was inhibited in mutant HMGB1^C106A cells. Furthermore, we performed a bimolecular fluorescence complementation assay to visualize Cys106 oxidation-induced HMGB1 dimerization in live cells exposed to oxidative stress and were able to reproduce the dimerization effect of HMGB1 in fluorescence resonance energy transfer analysis. Interestingly, dimerized HMGB1 bound to DNA with higher affinity than monomeric HMGB1. Dimerized HMGB1 protected DNA from damage due to hydroxyl free radicals and prevented cell death. In conclusion, dimerized HMGB1 may play a regulatory role in DNA stabilization under oxidative stress.

•

Accumulation of excessive ROS induces DNA damage, causing cell death.

•

HMGB1 dimerizes in the presence of excessive ROS and binds DNA with high affinity.

•

Binding of dimerized HMGB1 (Di-HMGB1) protects DNA from ROS action.

•

We prepared an in vitro HMGB1 dimerization due to excessive ROS.

•

Di-HMGB1 protected against DNA damage induced by radiation exposure.

Integration of Enzymatic Labeling with Single-Molecule Detection for Sensitive Quantification of Diverse DNA Damages

DNA damage plays an important role in the regulation of gene expression and disease processes. The accurate measurement of DNA damage is essential to the discovery of potential disease biomarkers for risk assessment, early clinical diagnosis, and therapy monitoring. However, the low abundance, random location in genomic elements, diversity, and the incapability to specifically amplify the DNA damages hinder the accurate quantification of various DNA damages within human genomes. Herein, we demonstrate the integration of enzymatic labeling with single-molecule detection for sensitive quantification of diverse DNA damages. A significant advantage of our method is that only the damaged base-containing DNA sequence can be labeled by the biotin-conjugated deoxynucleotide triphosphate (biotin-dNTP) and separated from the normal DNAs, which greatly improves the detection specificity. In addition, high sensitivity can be achieved by the terminal deoxynucleotidyl transferase (TdT)-induced polymerization of multiple Alexa Fluor 488-labeled-deoxyuridine triphosphates (AF488-dUTPs) and the introduction of single-molecule detection. This method can measure DNA damage with a detection limit as low as 1.1 × 10^-16 M, and it can distinguish DNA damage at low abundance down to 1.3 × 10^-4%. Importantly, it can provide information about the occurrence of DNA damage in a specific gene and ascertain the DNA damage level in different cancer cell lines, offering a new approach for studying the physiological function of various DNA damages in human diseases.

Mini Review of TiO2 -Based Multifunctional Nanocomposites for Near-Infrared Light-Responsive Phototherapy

Phototherapy with the properties of specific spatial/temporal selectivity and minimal invasiveness has been acknowledged as one of the most promising cancer therapy types. Among all the photoactive substance for phototherapy, titanium dioxide (TiO₂ ) nanomaterials are paid more and more attention due to their outstanding photocatalytic properties, prominent biocompatibility, and excellent chemical stability. However, the wide bandgap (3.0-3.2 eV) of TiO₂ limits its absorption only to the ultraviolet (UV) light region. For a long time, UV light-stimulated TiO₂ was applied in the phototherapy researches of tumors located in the skin layer, while it is unsatisfactory for most deep-tissue tumors. Due to the maximum penetration into tissue existing in the near-infrared (NIR) region, how to use NIR light to trigger photochemical reaction of TiO₂ remains a big challenge. In this review, two strategies to develop and construct NIR-triggered TiO₂ -based nanocomposites (NCs) for phototherapy are summarized, and the relevant mechanism and background knowledge of TiO₂ -based phototherapy are also given in order to better understand the application value and current situation of TiO₂ in phototherapy. Finally, the challenges and research directions of TiO₂ in the future clinic phototherapy application are also discussed.

Mutagenic and carcinogenic structural alerts and their mechanisms of action

Knowing the mutagenic and carcinogenic properties of chemicals is very important for their hazard (and risk) assessment. One of the crucial events that trigger genotoxic and sometimes carcinogenic effects is the forming of adducts between chemical compounds and nucleic acids and histones. This review takes a look at the mechanisms related to specific functional groups (structural alerts or toxicophores) that may trigger genotoxic or epigenetic effects in the cells. We present up-to-date information about defined structural alerts with their mechanisms and the software based on this knowledge (QSAR models and classification schemes).

Prolonged inflammatory microenvironment is crucial for pro-neoplastic growth and genome instability: a detailed review

INTRODUCTION

Chronic inflammation can affect the normal cell homeostasis and metabolism by rendering the cells susceptible to genomic instability that may lead to uncontrolled cellular growth and proliferation ensuing tumorigenesis. The causal agents for inflammation may be pathogenic infections like microbial agents ranging from viruses to bacteria. These infections lead to DNA damage or disruption of normal cell metabolism and alter the genome integrity.

FINDINGS

In this review, we have highlighted the role of recurrent infections in tumor microenvironment can lead to recruitment of pro-inflammatory cells, cytokines and growth factors to the site of inflammation. This makes the environment rich in cytokines, chemokines, DNA-damaging agents (ROS, RNS) and growth factors which activate DNA damage response pathway and help in sustained proliferation of the tumor cells. In any inflammatory response, the production of cytokines and related signaling molecules is self-regulating and limiting. But in case of neoplastic risk, deregulation of these factors may lead to abnormalities and related pathogenesis.

CONCLUSION

The scope of the present review is to explore the probable mechanistic link and factors responsible for chronic inflammation. The relation between chronic inflammation and DNA damage response was further elucidated to understand the mechanism by which it makes the cells susceptible to carcinogenesis.

Study on the mechanism of action between dimethyl phthalate and herring sperm DNA at molecular level

Dimethyl phthalate (DMP), a typical phthalic acid ester, is widespread in the environment and causes extensive concern due to its adverse effects on human health. To understand the genotoxicity of DMP at molecular level, the toxic interaction of DMP with herring sperm (hs) deoxyribonucleic acid (DNA; hs-DNA) was investigated in vitro under simulated physiological conditions using multi-spectroscopic techniques and a molecular modeling method. The results of Ultraviolet-Visible absorption spectroscopy, fluorescence emission spectroscopy, and circular dichroism spectra indicated that DMP interacts with hs-DNA in a groove-binding mode that changes the double helical structure of DNA. The binding constant and the number of binding sites calculated from the fluorescence quenching data were 565.718 L mol(-1) and 0.7872, respectively. A molecular modeling study revealed that DMP tends to bind with DNA in the A-T-rich regions of minor groove and that hydrogen bonding and van der Waals forces play main roles in the interaction. This research can help to elucidate the mechanism of DMP toxicity in vivo.

Helicobacter pylori-induced chronic inflammation causes telomere shortening of gastric mucosa by promoting PARP-1-mediated non-homologous end joining of DNA

Helicobacter pylori infection leads to chronic gastritis and increased risk of gastric cancer. The mechanism involves chronic inflammation. We aimed to determine the mechanism by which H. pylori infection causes telomere shortening in inflammatory gastric mucosa. Gastric biopsy specimens were obtained from 20 patients with chronic gastritis or peptic ulcer caused by H. pylori infection. The specimens showed increased NF-κB and superoxide dismutase activities and elevated expressions of PARP-1 and γ-H2AX, all of which returned to normal levels after anti-H. pylori treatment, suggesting that oxidative DNA damage and PARP-1 overexpression might cause telomere shortening. In this report, we adopted DNA end joining assay and showed that H. pylori-infected gastric mucosa had increased alternative NHEJ (non-homologous end joining), implicating that telomere shortening was caused by inflammation-mediated overproduction of reactive oxygen species and PARP-1, leading to telomere shortening.

New design of nucleotide excision repair (NER) inhibitors for combination cancer therapy

Many cancer chemotherapy agents act by targeting the DNA of cancer cells, causing substantial damage within their genome and causing them to undergo apoptosis. An effective DNA repair pathway in cancer cells can act in a reverse way by removing these drug-induced DNA lesions, allowing cancer cells to survive, grow and proliferate. In this context, DNA repair inhibitors opened a new avenue in cancer treatment, by blocking the DNA repair mechanisms from removing the chemotherapy-mediated DNA damage. In particular, the nucleotide excision repair (NER) involves more than thirty protein-protein interactions and removes DNA adducts caused by platinum-based chemotherapy. The excision repair cross-complementation group 1 (ERCC1)-xeroderma pigmentosum, complementation group A (XPA) protein (XPA-ERCC1) complex seems to be one of the most promising targets in this pathway. ERCC1 is over expressed in cancer cells and the only known cellular function so far for XPA is to recruit ERCC1 to the damaged point. Here, we build upon our recent advances in identifying inhibitors for this interaction and continue our efforts to rationally design more effective and potent regulators for the NER pathway. We employed in silico drug design techniques to: (1) identify compounds similar to the recently discovered inhibitors, but more effective at inhibiting the XPA-ERCC1 interactions, and (2) identify different scaffolds to develop novel lead compounds. Two known inhibitor structures have been used as starting points for two ligand/structure-hybrid virtual screening approaches. The findings described here form a milestone in discovering novel inhibitors for the NER pathway aiming at improving the efficacy of current platinum-based therapy, by modulating the XPA-ERCC1 interaction.

Antioxidant and DNA Damage Protecting Activity of Exopolysaccharides from the Endophytic Bacterium Bacillus cereus SZ1

An endophytic bacterium was isolated from the Chinese medicinal plant Artemisia annua L. The phylogenetic and physiological characterization indicated that the isolate, strain SZ-1, was Bacillus cereus. The endophyte could produce an exopolysaccharide (EPS) at 46 mg/L. The 1,1-diphenyl-2-picrylhydracyl (DPPH) radical scavenging activity of the EPS reached more than 50% at 3-5 mg/mL. The EPS was also effective in scavenging superoxide radical in a concentration dependent fashion with an EC50 value of 2.6 mg/mL. The corresponding EC50 for scavenging hydroxyl radical was 3.1 mg/mL. Moreover, phenanthroline-copper complex-mediated chemiluminescent emission of DNA damage was both inhibited and delayed by EPS. The EPS at 0.7-1.7 mg/mL also protected supercoiled DNA strands in plasmid pBR322 against scission induced by Fenton-mediated hydroxyl radical. The preincubation of PC12 cells with the EPS prior to H₂O₂ exposure increased the cell survival and glutathione (GSH) level and catalase (CAT) activities, and decreased the level of malondialdehyde (MDA) and lactate dehydrogenase (LDH) activity in a dose-dependent manner, suggesting a pronounced protective effect against H₂O₂-induced cytotoxicity. Our study indicated that the EPS could be useful for preventing oxidative DNA damage and cellular oxidation in pharmaceutical and food industries.

Selective Detection of 8-Oxo-2'-deoxyguanosine in Single-Stranded DNA via Nanopore Sensing Approach

We have developed a nanopore sensing approach for the selective detection of 8-oxo-2'-deoxyguanosine (8-oxoG) in single-stranded DNA. First, 1,12-dodecanediamine is coupled with 8-oxoG-containing DNA molecules in high yield which leaves a free amine group for subsequent attaching of an adamantane moiety. After incubation with cucurbit[7]uril, the host-guest complex-modified DNA hybrid is translocated through an α-hemolysin nanopore. Highly characteristic events can be recorded and used to quantify the 8-oxoG-DNA content in a DNA mixture. Compared with the existing methods, this study provides a reliable, quick, and low-cost approach for the detection of 8-oxoG site in single-stranded DNA at the single-molecule level, particularly suitable for high-throughput screening of a massive number of samples.

The oxidation of p-phenylenediamine, an ingredient used for permanent hair dyeing purposes, leads to the formation of hydroxyl radicals: Oxidative stress and DNA damage in human immortalized keratinocytes

The hair-dyeing ingredient, p-phenylenediamine (PPD), was previously reported to be mutagenic, possibly by inducing oxidative stress. However, the exact mechanism of PPD in inducing oxidative stress upon skin exposure during hair-dyeing in human keratinocytes remains unknown. The aim of our studies was therefore to investigate the toxicity of PPD and its by-products in human immortalized keratinocytes (HaCaT) after auto-oxidation and after reaction with hydrogen peroxide (H2O2). We found that the PPD half maximal effective cytotoxic concentration (EC50) to HaCaT is 39.37 and 35.63 μg/mL after 24 and 48 h, respectively, without addition of H2O2 to induce oxidation. When PPD (10 or 100 μg/mL) is combined with 10.5 μg/mL of H2O2, intracellular ROS production by HaCaT after 1 h was significantly increased and enhanced levels of DNA damage were observed after 4 h of exposure. After 24 h incubations, 20 μg/mL of PPD increased the level of DNA oxidation in HaCaT. Also, we found that the in vitro reaction between PPD and H2O2, even below the maximum allowance by cosmetic industries, released hydroxyl radicals which can damage DNA. Taken together, we conclude that PPD alone and when combined with H2O2 increases the formation of reactive oxygen species in human keratinocytes, leading to oxidative stress and subsequent DNA damage. These alterations suggest that the mechanism by which PPD exposure, alone or combined with H2O2, damages keratinocytes by the formation of the high reactive HO∙ radicals.

Endophytic fungi with antitumor activities: Their occurrence and anticancer compounds

Plant endophytic fungi have been recognized as an important and novel resource of natural bioactive products, especially in anticancer application. This review mainly deals with the research progress on the production of anticancer compounds by endophytic fungi between 1990 and 2013. Anticancer activity is generally associated with the cytotoxicity of the compounds present in the endophytic fungi. All strains of endophytes producing antitumor chemicals were classified taxonomically and the genera of Pestalotiopsis and Aspergillus as well as the taxol producing endophytes were focused on. Classification of endophytic fungi producing antitumor compounds has received more attention from mycologists, and it can also lead to the discovery of novel compounds with antitumor activity due to phylogenetic relationships. In this review, the structures of the anticancer compounds isolated from the newly reported endophytes between 2010 and 2013 are discussed including strategies for the efficient production of the desired compounds. The purpose of this review is to provide new directions in endophytic fungi research including integrated information relating to its anticancer compounds.

Viral infection-oxidative stress/DNA damage-aberrant DNA methylation: separate or interrelated events responsible for genetic instability and childhood ALL development?

Acute lymphoblastic leukemia (ALL) is a malignant disorder that originates in a single B- or T-lymphocyte progenitor and is characterized by a range of numeric and structural chromosomal aberrations. Although, so far no clear cause can be found for ALL the most commonly recognized and strongest causal factor is infection. However, an interesting question is how viral infection may be responsible for genetic changes that lead to lymphoid cell transformation. A plausible mechanism by which infection might impact the process of leukemogenesis via genetic alteration is through: oxidative stress/DNA damage which is closely linked with inflammation, aberrant expression of AID/ABOBEC family enzymes which may be responsible for massive mutation introduction and alteration of DNA methylation, leading to changes in the expression of hematopoietic genes. In this review we propose several specific molecular mechanisms which link infection with all the above-mentioned processes. The most likely event which links common virus infection with ALL pathogenesis is aberrant expression of AID/APOBEC. This event may be directly responsible for the introduction of point mutations (as the result of cytosine or 5-methylcytosine deamination and formation of G:U or G:T misspairs) as well as changes in DNA methylation status.

In vitro and in vivo antioxidant and antimutagenic activities of polyphenols extracted from hops (Humulus lupulus L.)

BACKGROUND

Hops (Humulus lupulus L.) contain 40-140 mg g(-1) polyphenols. The objective of this study was to determine the phenolic composition of a high-purity (total phenolic content = 887 mg g(-1) ) hop polyphenol extract (HPE) and evaluate its antioxidant activities in vivo and in vitro and its antimutagenic activity. The antioxidant activity of HPE was compared with the activity of green tea polyphenols.

RESULTS

The phenolic compositions of HPE were more than 55% proanthocyanidins and more than 28% flavonoid glycosides. In vitro, HPE effectively scavenged α,α-diphenyl-β-picrylhydrazyl, hydroxyl and superoxide anion radicals, and inhibited DNA oxidative damage. In vivo, oral HPE at a polyphenol dose of 200-800 mg kg(-1) body weight significantly prevented a bromobenzene-induced decrease in liver superoxide dismutase and glutathione peroxidase activity, and decreased levels of liver thiobarbituric acid reactive substances in bromobenzene-treated mice. An oral dose of 20-80 mg kg(-1) body weight HPE significantly reduced the frequency of bone marrow micronuclei induced by cyclophosphamide. The antioxidant activities of hop polyphenols in vitro and in vivo were higher than green tea polyphenols at the same concentration.

CONCLUSION

Hop polyphenols had the same or higher antioxidant activity than tea polyphenols. Hop polyphenols might be useful as natural antioxidants and antimutagens.

Simultaneous quantification of mitochondrial DNA copy number and deletion ratio: a multiplex real-time PCR assay

Mitochondrial dysfunction is implicated in a vast array of diseases and conditions, such as Alzheimer's disease, cancer, and aging. Alterations in mitochondrial DNA (mtDNA) may provide insight into the processes that either initiate or propagate this dysfunction. Here, we describe a unique multiplex assay which simultaneously provides assessments of mtDNA copy number and the proportion of genomes with common large deletions by targeting two mitochondrial sites and one nuclear locus. This probe-based, single-tube multiplex provides high specificity while eliminating well-to-well variability that results from assaying nuclear and mitochondrial targets individually.

Multi-spectroscopic methods combined with molecular modeling dissect the interaction mechanisms of ractopamine and calf thymus DNA

The toxic interaction of ractopamine (RAC) with calf thymus DNA (ct DNA) was studied in vitro using multi-spectroscopic methods and molecular modeling methods. The hypochromic effect without a noticeable shift in UV-vis absorption indicated that the minor groove binding mode existed in the interaction between RAC and DNA. The fluorescence quenching of RAC was observed with the increasing addition of DNA and was proved to be the static quenching. The binding constant and the binding site sizes were 4.13 × 10(3) and 0.97, respectively. The thermodynamic calculation demonstrated that the hydrogen bond and van der Waals were main acting forces. This result further confirmed the existence of groove binding mode. Afterwards, we found another interaction mode, electrostatic binding mode through the fluorescence polarization, ionic effects and denatured DNA experiments. Circular dichroism spectroscopy (CD) was then employed to monitor the conformation changes of DNA. Molecular modeling studies illustrated the visual display of the binding mode and the detailed information of the H-bond.

OFF-to-ON type fluorescent probe for the detection of 8-oxo-dG in DNA by the Adap-masked ODN probe

We have recently reported that Adap (adenosine-1,3-diazaphenoxazine) is an artificial nucleoside analogue for the specific recognition by multiple hydrogen bonding and that its fluorescence is selectively quenched with 8-oxo-2'-deoxyguanosine (8-oxo-dG) in DNA. We now report the development of a new OFF-to-ON type FRET probe, in which one strand contains Adap and another contains natural nucleotides for the formation of a less stable double strand. Each strand was labeled with Cy3 or BHQ2 at the 5'-end or 3'-end, respectively. It was expected in this system that fluorescence of the duplex probe is first quenched by FRET, but the target DNA strand containing 8-oxo-dG at the complementary site of Adap would enhance the displacement reaction of the less stable duplex probe that results in the fluorescence recovery. The results showed that the duplex probe containing the Adap-T base pair exhibited a complete discrimination between 8-oxo-dG and dG in DNA by fluorescence enhancement.

8-Hydroxy-2'-deoxyguanosine is a prognostic mediator for cardiac event

BACKGROUND

DNA in the nucleus is one of the major targets of reactive oxygen species (ROS), and oxidative DNA damage has been implicated in the pathogenesis of chronic heart failure. 8-Hydroxy-2'-deoxyguanosine (8-OHdG) is produced from deoxyguanosine in DNA by ROS. The purpose of this present study was to examine the clinical significance of serum 8-OHdG levels in patients with heart failure.

METHODS

We measured serum 8-OHdG levels in 230 patients with chronic heart failure and 42 control subjects without heart failure by sandwich enzyme-linked immunosorbent assay. Patients were prospectively followed during a median follow-up period of 472 days with the end points of cardiac death or progressive heart failure requiring re-hospitalization.

RESULTS

Serum 8-OHdG concentrations were higher in patients with heart failure than in control subjects (P < 0·001) and increased with advancing New York Heart Association (NYHA) functional class (P < 0·001). Normal upper limit of 8-OHdG level was determined as mean ± 2SD value from 42 control subjects (0·40 ng mL(-1)). Abnormally high serum 8-OHdG levels (> 0·40 ng mL(-1)) were observed in 21·2%, 43·1%, 42·6% and 69·4% through NYHA I to IV (P < 0·001). A total of 66 cardiac events occurred during a follow-up period, and Kaplan-Meier survival curves demonstrated that cardiac event rate was markedly higher in patients with high 8-OHdG levels than in those with normal 8-OHdG levels (62·4% vs. 29·6%, P = 0·0007).

CONCLUSIONS

Serum 8-OHdG levels provide important prognostic information for the risk stratification of patients with heart failure.

Adenosine-1,3-diazaphenoxazine derivative for selective base pair formation with 8-oxo-2'-deoxyguanosine in DNA

The selective detection of 8-oxo-2'-deoxyguanosine (8-oxo-dG) in DNA without chemical or enzymatic treatment is an attractive tool for genomic research. We designed and synthesized the non-natural nucleoside analogue, the adenosine-1,3-diazaphenoxazine (Adap) derivative, for selective recognition of 8-oxo-dG in DNA. This study clearly showed that Adap has a highly selective stabilizing effect on the duplex containing the Adap-8-oxo-dG base pair. Furthermore, the fluorescent property of Adap was shown to be useful for the selective detection of 8-oxo-dG in the duplex DNA. To the best of our knowledge, this is the first successful demonstration of a non-natural nucleoside with a high selectivity for 8-oxo-dG in DNA.

Improved in vitro assays of superoxide anion and 1,1-diphenyl- 2-picrylhydrazyl (DPPH) radical-scavenging activity of isoflavones and isoflavone metabolites

Free radical-scavenging activity of isoflavones and some isoflavone metabolites have been described previously, but the results are inconsistent. The objective of the present study was to find out the pivotal factors that influence an accurate detection of both superoxide anion and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity. We here showed for the first time that organic solvents, including methanol, ethanol and acetone, were of strong superoxide radical-scavenging activity at concentrations down to 0.1% (v/v), however, no such activity was observed with acetonitrile at concentrations up to 2.0% (v/v). In DPPH assay, we found that the DPPH radical-scavenging ratio increased together with the extended reaction time. Based on our findings, improved in vitro assays for the detection of radical-scavenging activity of both isoflavones (daidzein and genistein) and isoflavone metabolites, including dihydrodaidzein (DHD), dihydrogenistein (DHG), and O-desmethylangolensin (O-Dma), were established.

Increased plasma levels of 8-hydroxydeoxyguanosine are associated with development of colorectal tumors

Increased oxidative stress is generally thought to be associated with tumorigenesis. In this cross-sectional study, we evaluated plasma 8-hydroxydeoxyguanosine (8-OHdG) levels in patients with colorectal adenoma and cancer, as a surrogate marker of oxidative damage to deoxyribonucleic acid (DNA). We collected blood samples from 58 patients with adenoma, 32 with early cancer, 25 with advanced cancer, and 36 without polyps or cancer (as controls), and measured plasma levels of 8-OHdG by enzyme-linked immunosorbent assay. Univariate analysis by logistic regression showed that an increased level of 8-OHdG was a significant risk for adenoma [odds ratio (OR) 1.393, 95% confidence interval (CI) 1.008-1.926, p = 0.045]. In patients with early cancer, univariate analysis revealed significant differences for age, body mass index (BMI), systolic blood pressure, and 8-OHdG level. Subsequent multivariate analysis revealed that 8-OHdG [OR 1.627, 95% CI 1.079-2.453, p = 0.020] and BMI [OR 1.283, 95% CI 1.038-1.585, p = 0.021] were significant risk factors for early cancer. However, 8-OHdG was not a significant risk factor for advanced cancer. Our results suggest that an increased plasma level of 8-OHdG is associated with development of colorectal adenoma and cancer.

Repair activities of human 8-oxoguanine DNA glycosylase are stimulated by the interaction with human checkpoint sensor Rad9-Rad1-Hus1 complex

Rad9-Rad1-Hus1 (9-1-1) is a checkpoint protein complex playing roles in DNA damage sensing, cell cycle arrest, DNA repair or apoptosis. Human 8-oxoguanine DNA glycosylase (hOGG1) is the major DNA glycosylase responsible for repairing a specific aberrantly oxidized nucleotide, 7,8-dihydro-8-oxoguanine (8-oxoG). In this study, we identified a novel interaction between hOGG1 and human 9-1-1, and investigated the functional consequences of this interaction. Co-immunoprecipitation assays using transiently transfected HEK293 cells demonstrated an interaction between hOGG1 and the 9-1-1 proteins. Subsequently, GST pull-down assays using bacterially expressed and purified hOGG1-His and GST-fused 9-1-1 subunits (GST-hRad9, GST-hRad1, and GST-hHus1) demonstrated that hOGG1 interacted directly with the individual subunits of the human 9-1-1 complex. In vitro excision assay, which employed a DNA duplex containing an 8-oxoG/C mismatch, showed that hRad9, hRad1, and hHus1 enhanced the 8-oxoG excision and beta-elimination activities of hOGG1. In addition, the presence of hRad9, hRad1, and hHus1 enhanced the formation of covalently cross-linked hOGG1-8-oxoG/C duplex complexes, as determined by a trapping assay using NaBH(4). A trimeric human 9-1-1 complex was purified from Escherichia coli cell transformed with hRad9, His-fused hRad1, or His-fused hHus1 expressing vectors. It also showed the similar activity to enhance in vitro hOGG1 glycosylase activity, compared with individual human 9-1-1 subunits. Detection of 8-oxoG in HEK293 cells using flow cytometric and spectrofluorometric analysis revealed that over-expression of hOGG1 or human 9-1-1 reduced the formation of 8-oxoG residues following the H(2)O(2) treatment. The highest 8-oxoG reduction was observed in HEK293 cells over-expressing hOGG1 and all the three subunits of human 9-1-1. These indicate that individual human 9-1-1 subunits and human 9-1-1 complex showed almost the same abilities to enhance the in vitro 8-oxoG excision activity of hOGG1, but that the greatest effect to remove 8-oxoG residues in H(2)O(2)-treated cells was derived from the 9-1-1 complex as a whole.

Evaluation of DNA damage by the alkaline comet assay of the olfactory and respiratory epithelia of dogs from the city of São Paulo, Brazil

Animals kept as pets may be considered sentinels for environmental factors to which humans could be exposed. Olfactory and respiratory epithelia are directly subjected to airborne factors, which could cause DNA lesions, and the alkaline comet assay is considered a reliable tool for the assessment of DNA damage. The objective of this work is to evaluate the extent of DNA damage by the comet assay of the olfactory and respiratory epithelia of dogs from different regions of the city of São Paulo, Brazil. Thirty-three clinically healthy dogs, aged 5 years or more, were used in the study, with 7 from the North region of São Paulo, 7 from the South region, 3 dogs from the East region, and 16 dogs from the West city region. Three dogs younger than 6 months were used as controls. DNA damage was analyzed by the alkaline comet assay. We observed no difference in histopathological analysis of olfactory and respiratory epithelia between dogs from different regions of São Paulo. Dogs older than 5 years presented significantly higher comet length in both olfactory and respiratory epithelia, when compared with controls, indicating DNA damage. When separated by regions, olfactory and respiratory epithelia presented similar DNA damage in dogs from different regions of São Paulo, corroborating with similar levels of particulate matter index (PM10) in all regions of the city. In this study, we report for the first time that the comet assay can be used to quantify the extent of DNA damage in dog olfactory and respiratory epithelia, and that comet length (DNA damage) increases with age, probably due to environmental factors. Air pollution, as measured by PM10, can be responsible for this DNA damage.

Use of conventional and -omics based methods for health claims of dietary antioxidants: a critical overview

This article describes the principles and limitations of methods used to investigate reactive oxygen species (ROS) protective properties of dietary constituents and is aimed at providing a better understanding of the requirements for science based health claims of antioxidant (AO) effects of foods. A number of currently used biochemical measurements aimed of determining the total antioxidant capacity and oxidised lipids and proteins are carried out under unphysiological conditions and are prone to artefact formation. Probably the most reliable approaches are measurements of isoprostanes as a parameter of lipid peroxidation and determination of oxidative DNA damage. Also the design of the experimental models has a strong impact on the reliability of AO studies: the common strategy is the identification of AO by in vitro screening with cell lines. This approach is based on the assumption that protection towards ROS is due to scavenging, but recent findings indicate that activation of transcription factors which regulate genes involved in antioxidant defence plays a key role in the mode of action of AO. These processes are not adequately represented in cell lines. Another shortcoming of in vitro experiments is that AO are metabolised in vivo and that most cell lines are lacking enzymes which catalyse these reactions. Compounds with large molecular configurations (chlorophylls, anthocyans and polyphenolics) are potent AO in vitro, but weak or no effects were observed in animal/human studies with realistic doses as they are poorly absorbed. The development of -omics approaches will improve the scientific basis for health claims. The evaluation of results from microarray and proteomics studies shows that it is not possible to establish a general signature of alterations of transcription and protein patterns by AO. However, it was shown that alterations of gene expression and protein levels caused by experimentally induced oxidative stress and ROS related diseases can be normalised by dietary AO.

Selective fluorescence quenching of the 8-oxoG-clamp by 8-oxodeoxyguanosine in ODN

The 8-oxoG-clamp, a specific fluorescent probe for 8-oxo-deoxyguanosine (8-oxo-dG), was incorporated into the oligodeoxynucleotide (ODN) within or at the 3'-end of the purine and the pyrimidine sequences. Based on the UV-melting temperature, the 8-oxoG-clamp showed slightly lower stabilizing effects on the duplexes containing 8-oxo-dG at the complementary site than that with dG. On the other hand, 8-oxo-dG in DNA was selectively detected by fluorescence quenching of the 8-oxoG-clamp.

Human ribosomal protein S3 (hRpS3) interacts with uracil-DNA glycosylase (hUNG) and stimulates its glycosylase activity

Human ribosomal protein S3 (hRpS3) is a small ribosomal subunit showing apurinic/apyrimidinic (AP) lyase activity and has been suggested to play a role in the cellular DNA-damage response pathway. However, the functional interactions between hRpS3 and other base excision repair (BER) DNA glycosylases have not been reported. We identified, for the first time, the interaction between hRpS3 and human uracil-DNA glycosylase (hUNG) and investigated the functional consequences of this interaction. hRpS3 was shown to interact with hUNG in co-immunoprecipitation assay using transiently transfected HEK293 cells and GST pull-down assay using microbial expression systems. In an assay using a 5'-end-radiolabeled 39-mer oligonucleotide duplex containing a U/G mismatch, hRpS3 dramatically stimulated the uracil-excision activity of hUNG, whereas hRpS3 alone had no cleavage activity. Pre-incubation of hRpS3 with the U/G mismatch containing DNA duplex also increased the hUNG uracil-excision activity; however, hRpS3 did not increase the DNA binding activity of hUNG in a trapping assay of hUNG and the U/G mismatch containing DNA duplex using UV cross-linking. hRpS3 has been suggested to stimulate the uracil-excision activity of hUNG by enhancing its dissociation from AP sites and increasing its turn-over rate. The disruption of hRpS3 by small-interfering RNA (siRNA-hRpS3) transfection reduced the uracil-excision activity preserved in cell extracts, whereas the supplement of purified hRpS3 retained uracil-excision activity. These results strongly suggest that hRpS3 may be involved in the uracil-excision pathway, probably by participating in the DNA repair mechanism to remove uracil generated by the deamination of cytosine in DNA, and by preventing C/G-->T/A transition mutations.

Binding to the minor groove of the double-strand, tau protein prevents DNA from damage by peroxidation

Tau, an important microtubule associated protein, has been found to bind to DNA, and to be localized in the nuclei of both neurons and some non-neuronal cells. Here, using electrophoretic mobility shifting assay (EMSA) in the presence of DNA with different chain-lengths, we observed that tau protein favored binding to a 13 bp or a longer polynucleotide. The results from atomic force microscopy also showed that tau protein preferred a 13 bp polynucleotide to a 12 bp or shorter polynucleotide. In a competitive assay, a minor groove binder distamycin A was able to replace the bound tau from the DNA double helix, indicating that tau protein binds to the minor groove. Tau protein was able to protect the double-strand from digestion in the presence of DNase I that was bound to the minor groove. On the other hand, a major groove binder methyl green as a negative competitor exhibited little effect on the retardation of tau-DNA complex in EMSA. This further indicates the DNA minor groove as the binding site for tau protein. EMSA with truncated tau proteins showed that both the proline-rich domain (PRD) and the microtubule-binding domain (MTBD) contributed to the interaction with DNA; that is to say, both PRD and MTBD bound to the minor groove of DNA and bent the double-strand, as observed by electron microscopy. To investigate whether tau protein is able to prevent DNA from the impairment by hydroxyl free radical, the chemiluminescence emitted by the phen-Cu/H₂O₂/ascorbate was measured. The emission intensity of the luminescence was markedly decreased when tau protein was present, suggesting a significant protection of DNA from the damage in the presence of hydroxyl free radical.

Lesion specificity in the base excision repair enzyme hNeil1: modeling and dynamics studies

Base excision repair (BER) is the major pathway employed to excise oxidized DNA lesions. Human Neil1, a versatile glycosylase in the BER pathway, repairs a diverse array of oxidative lesions; however, the most prevalent, 8-oxo-7,8-dihydroguanine (8-oxoG), is only weakly excised. The structural origin of hNeil1's ability to repair a variety of lesions but not 8-oxoG is a model system for connecting enzyme structure and lesion-recognition specificity. To elucidate structural properties determining hNeil1's substrate specificities, we have investigated it in complex with two pairs of representative well-repaired substrates: the R- and S-spiroiminodihydantoin (Sp) stereoisomers, nonplanar further oxidation products of guanine, and the 5R,6S- and 5S,6R-thymine glycol (Tg) stereoisomers, the most prevalent oxidative lesions of thymine. We also investigate the poorly repaired 8-oxoG. We employed molecular modeling and 10 ns molecular dynamics (MD) simulations. The results of our investigations provide structural explanations for the ability of hNeil1 to excise a variety of oxidative lesions: they possess common chemical features, namely, a pyrimidine-like ring and shared hydrogen bond donor-acceptor properties, which allow the lesions to fit well in the binding pocket, which is somewhat flexible. However, the planar 8-oxoG is not as well accommodated in the shallow and comparatively cramped recognition pocket; it has fewer hydrogen bonding interactions with the enzyme and a solvent exposed six-membered ring, consistent with its poor repair susceptibility by this enzyme.

Chromatographic and electrophoretic methods for the analysis of biomarkers of oxidative damage to macromolecules (DNA, lipids, and proteins)

Free radicals and other reactive species can cause oxidative damage to biomolecules when oxidant species exceed the antioxidant defences in the body, resulting in oxidative stress. Oxidatively damaged products have been associated with aging as well as with the development of pathologies like cancer, cardiovascular disease, neurodegenerative disorders, diabetes, inflammation, etc. Reliable measurements of biomarkers of oxidative damage to macromolecules would afford information on the pre-disposition and prognosis of certain pathologies, being of utmost importance in evaluation of the effect of intervention with antioxidants on the incidence of diseases associated to oxidative stress. This review will present and compare different analytical methods, especially those involving chromatographic and electrophoretic techniques, commonly used for the analysis of biomarkers of oxidative damage to the three main macromolecules, namely oxidised DNA, lipid peroxidation products, and protein carbonyls.

Activity of grape extracts from Greek varieties of Vitis vinifera against mutagenicity induced by bleomycin and hydrogen peroxide in Salmonella typhimurium strain TA102

Several in vivo and in vitro studies have shown that grape extracts could prevent certain steps in carcinogenesis and a few mechanisms have been proposed for this activity. In this study, the potential antimutagenic activity of methanolic and aqueous extracts from two Greek grape varieties of Vitis vinifera against DNA damage induced by reactive oxygen species (ROS) was assessed as a potential novel chemopreventive mechanism, using Salmonella typhimurium strain TA102. The two grape varieties were Assyrtiko (white grapes) and Mandilaria (red grapes), while the oxidant mutagens used were bleomycin (BLM) and hydrogen peroxide (H(2)O(2)). Since it has been considered that polyphenols present in grapes are their most potent biologically active compounds, we also tested the effects of polyphenol-rich fractions as well as some of the more common grape polyphenols on the activity of the two test mutagens. These polyphenols were quercetin, (+)-catechin, (-)-epicatechin, trans-resveratrol, gallic acid and protocatechuic acid. Almost all extracts showed inhibitory activity against both mutagens. On the other hand, polyphenol-rich fractions as well as individual polyphenols at concentrations found in the extracts either did not diminish or did enhance the activity of the mutagens. These results suggest that the protection of DNA from mutations induced by ROS may be one of the mechanisms accounting for the chemopreventive activity of grape extracts. However, it seems that this protective activity may not be attributed to polyphenols but rather to a synergism of many compounds in the grapes.

Antigenotoxic effects of Satureja hortensis L. on rat lymphocytes exposed to oxidative stress

The protective properties of Satureja hortensis L. on the rat lymphocytes DNA lesions were tested. Lymphocytes were isolated from blood samples taken from healthy rats. DNA breaks and resistance to H2O2-induced damage were measured with the comet assay. Rat lymphocytes were incubated in S. hortensis ethanolic extract (SHE) (0.05, 0.1, 0.5, 1.0, and 2.5 mg/ mL), essential oil (SHEO)(0.05, 0.1, 0.5, 1.0, and 2.5 microL/mL), H2O2 (50, 100, and 200 microM), a combination of H2O2 (200 mM) with either SHE (1.0, 2.5 mg/mL) or SHEO (1.0, 2.5 microL/mL) at 4 degrees C for 30 min, and the extent of DNA migration was measured using a single-cell microgel electrophoresis technique under alkaline conditions. Treatment of rat lymphocytes with SHE or SHEO resulted in significant reduction of H2O2-induced DNA damage compared to controls. SHE exhibited a significant (P < 0.01) inhibitory effect on oxidative DNA damage at 2.5 mg/mL. SHEO (1.0 and 2.5 microL/mL) also showed significant inhibitory effects (P < 0.01) on H2O2 induced chromosomal damage. In conclusion both the ethanolic extract and the essential oil of the plant reversed the oxidative damage to rat lymphocytes induced by hydrogen peroxide.

8-Hydroxy-2'-deoxyguanosine as a marker of oxidative DNA damage related to occupational and environmental exposures

Oxidative DNA damage is considered to play an important role in pathophysiological processes, ageing and cancer. So far major interest has been on measuring 8-hydroxy-2'-deoxyguanosine (8-OHdG), the preferred methods relying on HPLC or GC-mass spectrometry. The high biological relevance of 8-OHdG is due to its ability to induce G-->T transversions, which are among the most frequent somatic mutations found in human cancers. Effects of workplace exposures on the level of white blood cell 8-OHdG or urinary 8-OHdG have been reported with controversial results. Exposures examined include asbestos, azo-dyes, benzene, fine particulate matter (PM(2.5)), glassworks, polycyclic aromatic hydrocarbons (PAHs), rubber manufacturing, silica, metals, styrene, toluene and xylenes. The available data indicate that there is still a lack of well established dose-response relations between occupational or environmental exposures and the induction of 8-OHdG. Smoking has been most consistently identified as a confounder for 8-OHdG, but various occupational studies did not reveal higher levels of 8-OHdG in smokers. Despite the conflicting results, the reported studies show promise for 8-OHdG as a biomarker of oxidative stress associated with chemical exposure. However, there are critical aspects related to the analytical challenge, artifactual production of 8-OHdG, inter- and intra-individual variation, confounding factors and inter-laboratory differences, implying that further work is needed to reach a consensus on the background level of 8-OHdG.

Oxidative damage in cerebral vessels of diabetic db/db mice

BACKGROUND

Oxidative stress in diabetes mellitus has recently received increasing attention as it has been proven to be associated with the development of diabetic vascular complications. Our aim was to examine whether microvascular changes, including oxidative damage, were induced in the brains of diabetic animals.

METHODS

The expression of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a marker of oxidative DNA damage, the binding of cationized ferritin, a marker for evaluating endothelial glycocalyx, to the endothelial cells of capillaries and vascular permeability of intravenously injected horseradish peroxidase were examined in the cortices of 12- and 20-week-old db/db and db/+m mice.

RESULTS

Immunostaining for 8-OHdG was clearly seen in the vessels of the cortex of 20-week-old db/db mice, but was hardly seen in those of mice in the other groups. The immunopositive area of 8-OHdG was significantly increased in the cortex of 20-week-old db/db mice compared with that of 20-week-old db/+m mice. No extravasated leakage of horseradish peroxidase was seen in any groups of mice, while the numbers of cationized ferritin particles binding to the endothelial cells was significantly decreased in 12- and 20-week-old db/db mice compared with that of db/+m mice at the same age, respectively.

CONCLUSION

These findings suggest that changes in endothelial glycocalyx are induced in db/db mice and, in addition, the long-term diabetic condition of these mice induces oxidative DNA damage to the cerebral vessels.

Reactive oxygen species and human inflammatory periodontal diseases

Reactive oxygen species (ROS) have emerged as important signaling molecules in the regulation of various cellular processes. They can be generated by the mitochondrial electron transport chain in mitochondria and activation of polymorphonuclear leukocytes (PMN) during inflammatory conditions. Excessive generation of ROS may result in attack of and damage to most intracellular and extracellular components in a living organism. Moreover, ROS can directly induce and/or regulate apoptotic and necrotic cell death. Periodontal pathologies are inflammatory and degenerative diseases. Several forms of periodontal diseases are associated with activated PMN. Damage of tissues in inflammatory periodontal pathologies can be mediated by ROS resulting from the physiological activity of PMN during the phagocytosis of periodontopathic bacteria.

Does measurement of oxidative damage to DNA have clinical significance?

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

DNA repair is responsible for the presence of oxidatively damaged DNA lesions in urine

The repair of oxidatively damaged DNA is integral to the maintenance of genomic stability, and hence prevention of a wide variety of pathological conditions, such as aging, cancer and cardiovascular disease. The ability to non-invasively assess DNA repair may provide information regarding repair pathways, variability in repair capacity, and susceptibility to disease. The development of assays to measure urinary DNA lesions offered this potential, although it rapidly became clear that possible contribution from diet and cell turnover may influence urinary lesion levels. Whilst early studies attempted to address these issues, up until now, much of the data appears conflicting. However, recent work from our laboratories, in which human volunteers were fed highly oxidatively modified 15N-labelled DNA demonstrates that diet does not appear to contribute to urinary levels of 8-hydroxyguanine and 7,8-dihydro-8-oxo-2'-deoxyguanosine. Furthermore, we propose that a number of literature reports form an argument against a contribution from cell death. Indeed we, and others, have presented evidence, which strongly suggests the involvement of cell death to be minimal. Taken together, these data would appear to rule out various confounding factors, leaving DNA repair pathways as the principal source of urinary purine, if not DNA, lesions enabling such measurements to be used as indicators of repair.

Effects of cooking oil fumes on the genotoxicity and oxidative stress in human lung carcinoma (A-549) cells

This study investigates the genotoxicity and cytotoxicity of oil fumes, formed when peanut oil is heated, on human lung carcinoma pulmonary type II-like epithelium cells. The major mutagenic compound (trans-trans-2,4-decadienal, t-t-2,4-DDE) contained in oil fumes and its effect on the induction of reactive oxygen species (ROS) is also discussed. The results indicate that the methanolic extract of oil fumes can apparently lead to cytotoxicity and oxidative DNA damage. Glutathione (GSH) content, and the activities of antioxidative enzymes such as GSH reductase, GSH peroxidase and GSH S-transferase were adversely reduced by the methanolic extract of oil fumes. t-t-2,4-DDE could produce superoxide anion, hydrogen peroxide and hydroxyl radicals in a phosphate buffer (pH 7.4), and form intracellular ROS, determined by dichlorofluorescein assay in A-549 cells. Moreover, t-t-2,4-DDE caused significant (P <0.05) oxidative damage of the 8-hydroxy-2'-deoxyguanosine formation in A-549 cells at concentrations from 50 to 200 microM. These results demonstrated that the DNA damage in A-549 cells, induced by t-t-2,4-DDE, was related to the ROS formation. The occurrence of t-t-2,4-DDE, therefore, was of significance in the genotoxicity of oxidized oil and fumes.

Pro-oxidant environment of the colon compared to the small intestine may contribute to greater cancer susceptibility

The colon and small intestine have inherent differences (e.g. redox status) that may explain the variation in cancer occurrence at these two sites. This study examined basal and induced (oxidative challenge) reactive oxygen species (ROS) generation, antioxidant enzyme activity and oxidative DNA damage. Basal ROS and antioxidant enzyme activities in the colon were greater than in the small intestine. During oxidative stress, 8-oxo-deoxyguanosine (8-oxodG) DNA adducts in the colon exceeded levels in the small intestine concomitant with increased ROS. Thus the colon responds to oxidative stress less effectively than the small intestine, possibly contributing to increased cancer incidence at this site.

Antigenotoxic effect of grape seed procyanidin extract in Fao cells submitted to oxidative stress

The protective effects of grape seed procyanidin extract on the repair of H(2)O(2)-induced DNA lesions were tested using Fao cells. Cells were exposed to 600 microM H(2)O(2) for 3 or 21 h. A procyanidin extract from grape seed (PE) was incubated or preincubated (1 h) during the exposure to H(2)O(2). The ability of procyanidins to protect against the genotoxicity of H(2)O(2) was compared with those of the monomeric flavanols (+)-catechin and (-)-epicatechin and the flavonol quercetin. After treatment, DNA damage was monitored using alkaline single-cell gel electrophoresis (the comet assay) (Aherne, S. A.; O'Brien, N. M. Nutr. Cancer 1999, 34, 160-166). At the end of the experiment, PE significantly decreased the damage caused by H(2)O(2). The results also showed that quercetin was the most effective of the flavonoids tested, which is consistent with its powerful antioxidant character. The results indicate that procyanidins are more effective than the corresponding individual monomers, catechin and epicatechin, at preventing DNA lesions in hepatocytes and that this protection is higher after preincubation than after co-incubation.