Oxidative damage to cellular and isolated DNA by metabolites of a fungicide ortho-phenylphenol

Controlling Gut Microbiota by Twendee X® May Contribute to Dementia Prevention

The human gut microbiota (GM) is a complex and dynamic ecosystem that hosts trillions of commensal and potentially pathogenic microorganisms. It is crucial in protecting humans from pathogens and in maintaining immune and metabolic homeostasis. Numerous studies have demonstrated that GM has a significant impact on health and disease, including Alzheimer's disease (AD). AD is a progressive neurodegenerative disorder characterized by impaired short-term memory and cognitive deficits. Patients with AD have been reported to exhibit abnormalities in GM density and species composition. Oxidative stress (OS) has been implicated in the onset and progression of AD; however, the relationship between OS and gut microbiota in AD onset and progression is not clear. Twendee X® (TwX), an oral supplement consisting of eight active ingredients, has been shown to prevent dementia in mild cognitive impairment (MCI) in humans and substantially improve cognitive impairment in mouse models of AD. This positive effect is achieved through the potency of the combined antioxidants that regulate OS; therefore, similar results cannot be achieved by a single antioxidant ingredient. To examine the impact of long-term OS elevation, as seen in AD on the body and GM, we examined GM alterations during the initial OS elevation using a two-week OS loading rat model, and examined the effects of TwX on OS and GM. Furthermore, using a questionnaire survey and fecal samples, we analyzed the impact of TwX on healthy individuals' gut bacteria and the associated effect on their quality of life (QOL). TwX was found to increase the number of bacteria species and their diversity in GM, as well as butyrate-producing bacteria, which tend to be reduced in AD patients. Additionally, TwX improved defecation condition and QOL. The gut bacteria function as part of the homeostatic function during OS elevation, and the prophylactic administration of TwX strengthened this function. The results suggest that the preventative effect of TwX on dementia may involve the GM, in addition to the other previously demonstrated effects.

Food additive-induced oxidative stress in rat male reproductive organs and hippocampus

As currently defined, the exposome represents the lifetime exposure measure of an individual to all potential external genetic influences and their impact on health. Although intentionally added chemicals (e.g., food additives) and food contact materials (e.g., packaging, pesticides) have been assessed for safety to some degree, the full extent to which they can affect health and reproduction has not been reported. The aim of this study was to determine the in vitro and in vivo effects of food additives on the male rat brain and sperm/testes, particularly through oxidative stress. Results from our in vitro study demonstrated that the administration of the common food additive, stevioside, a major component of the common sweetener stevia, as well as the preservatives, diphenyl and orthophenyl phenol (OPP), induced reactive oxygen species (ROS) production in sperm, and led to sperm dysfunction. These effects were inhibited by the addition of the antioxidant α-tocopherol. Moreover, OPP treatment (1/10,000 of no observed adverse effect) induced ROS production in sperm and lipid peroxidation in the epididymis and hippocampus after two weeks in vivo. Furthermore, 4-hydroxynonenal-positive cells, indicating ROS-generated protein modifications, were detected in spermatocytes in the testes and granular cell layer of the dentate gyrus in the brain. Treatment with α-tocopherol significantly improved oxidative stress. Our study suggests that certain food additives may affect sperm function and induce oxidative stress in the testes and brain, resulting in infertility and short-term memory loss, and some antioxidants may improve these dysfunctions.

Suppressing PARylation by 2',5'-oligoadenylate synthetase 1 inhibits DNA damage-induced cell death

High expression of 2',5'-oligoadenylate synthetase 1 (OAS1), which adds AMP residues in 2',5' linkage to a variety of substrates, is observed in many cancers as a part of the interferon-related DNA damage resistance signature (IRDS). Poly(ADP-ribose) (PAR) is rapidly synthesized from NAD⁺ at sites of DNA damage to facilitate repair, but excessive PAR synthesis due to extensive DNA damage results in cell death by energy depletion and/or activation of PAR-dependent programmed cell death pathways. We find that OAS1 adds AMP residues in 2',5' linkage to PAR, inhibiting its synthesis in vitro and reducing its accumulation in cells. Increased OAS1 expression substantially improves cell viability following DNA-damaging treatments that stimulate PAR synthesis during DNA repair. We conclude that high expression of OAS1 in cancer cells promotes their ability to survive DNA damage by attenuating PAR synthesis and thus preventing cell death.

Mechanism of oxidative DNA damage induced by metabolites of carcinogenic naphthalene

Naphthalene is a carcinogenic polycyclic aromatic hydrocarbon, to which humans are exposed as an air pollutant. Naphthalene is metabolized in humans to reactive intermediates such as 1,2-hydroxynaphthalene (1,2-NQH₂), 1,4-NQH₂, 1,2-naphthoquinone (1,2-NQ), and 1,4-NQ. We examined oxidative DNA damage by these naphthalene metabolites using ³²P-labeled DNA fragments from human cancer-relevant genes. 1,2-NQH₂ and 1,4-NQH₂ induced DNA damage in the presence of Cu(II). The DNA-damaging activity of 1,2-NQH₂ was significantly increased in the presence of the reduced form of nicotinamide adenine dinucleotide (NADH), whereas that of 1,4-NQH₂ was not. In the presence of NADH, 1,2-NQ induced Cu(II)-dependent DNA damage, whereas 1,4-NQ did not. The calculated energy of the lowest unoccupied molecular orbital (LUMO), which corresponds to the reduction potential, was estimated to be -0.67 eV for 1,2-NQ and -0.75 eV for 1,4-NQ. These results suggest that 1,2-NQ was reduced more easily than 1,4-NQ. Furthermore, 1,2-NQH₂, 1,4-NQH₂, and 1,2-NQ plus NADH formed 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) as an oxidative DNA marker. Catalase and bathocuproine inhibited DNA damage, suggesting that H₂O₂ and Cu(I) were involved. These results indicate that NQH₂s are oxidized to the corresponding NQs via semiquinone radicals, and that H₂O₂ and Cu(I) are generated during oxidation. 1,2-NQ is reduced by NADH to form the redox cycle, resulting in enhanced DNA damage. The formation of the corresponding semiquinone radicals was supported by an electron paramagnetic resonance (EPR) study. In conclusion, the redox cycle of 1,2-NQ/1,2-NQH₂ may play a more important role in the carcinogenicity of naphthalene than that of 1,4-NQ/1,4-NQH₂.

Gene-diet interactions in exposure to heterocyclic aromatic amines and bulky DNA adduct levels in blood leukocytes

Heterocyclic aromatic amines (HAAs), carcinogens produced in meat when cooked at high temperatures, are an emerging biologic explanation for the meat-colorectal cancer relationship. HAAs form DNA adducts; left unrepaired, adducts can induce mutations, which may initiate/promote carcinogenesis. The purpose of this research was to investigate the relationship between dietary HAAs, genetic susceptibility and bulky DNA adduct levels. Least squares regression was used to examine the relationship between dietary HAA exposure and bulky DNA adduct levels in blood measured using (32)P-postlabeling among 99 healthy volunteers. Gene-diet interactions between dietary HAAs and genetic factors relevant to the biotransformation of HAAs and DNA repair were also examined. No main effects of dietary HAAs on bulky DNA adduct levels was found. However, those with the putative NAT1 rapid acetylator phenotype had lower adduct levels than those with the slow acetylator phenotype (P = 0.02). Furthermore, having five or more 'at-risk' genotypes was associated with higher bulky DNA adduct levels (P = 0.03). Gene-diet interactions were observed between NAT1 polymorphisms and dietary HAAs (P < 0.05); among the slow acetylator phenotype, higher intakes of HAAs were associated with an increase in DNA adduct levels compared to lower intakes. This study provides evidence of a biologic relationship between dietary HAAs, genetic susceptibility and bulky DNA adduct formation. However, the lack of a strong main effect of HAAs suggests that dietary HAAs are not a large contributor to bulky DNA adducts in this population; future studies should consider relevant gene-diet interactions to clarify the role of HAAs in carcinogenesis.

Romidepsin (FK228), a potent histone deacetylase inhibitor, induces apoptosis through the generation of hydrogen peroxide

Romidepsin (FK228) is a potent histone deacetylase (HDAC) inhibitor, which has a potent anticancer activity, but its molecular mechanism is unknown. We investigated the mechanism of FK228-induced apoptosis in the human leukemia cell line HL-60 and its hydrogen peroxide (H(2)O(2))-resistant sub-clone, HP100, and the human colon cancer cell line Caco-2. Cytotoxicity and DNA ladder formation induced by FK228 could be detected in HL-60 cells after a 24-h incubation, whereas they could not be detected in HP100 cells. Trichostatin A (TSA), an HDAC inhibitor, induced DNA ladder formation in both HL-60 and HP100 cells. In contrast, FK228 inhibited HDAC activity in both HL-60 and HP100 cells to a similar extent. These findings suggest that FK228-induced apoptosis involves H(2)O(2)-mediated pathways and that TSA-induced apoptosis does not. Flow cytometry revealed H(2)O(2) formation and a change in mitochondrial membrane potential (Δψm) in FK228-treated cells. FK228 also induced apoptosis in Caco-2 cells, which was prevented by N-acetyl-cysteine, suggesting that reactive oxygen species participate in apoptosis in various types of tumor cells. Interestingly, in a cell-free system, FK228 generated superoxide (O(2)(-)) in the presence of glutathione, suggesting that H(2)O(2) is derived from dismutation of O(2)(-) produced through redox-cycle of FK228. Therefore, in addition to HDAC inhibition, H(2)O(2) generated from FK228 may participate in its apoptotic effect.

DNA damage and estrogenic activity induced by the environmental pollutant 2-nitrotoluene and its metabolite

OBJECTIVES

The environmental pollutant 2-nitrotoluene (2-NO(2)-T) is carcinogenic and reproductively toxic in animals. In this study, we elucidated the mechanisms of its carcinogenicity and reproductive toxicity.

METHODS

We examined DNA damage induced by 2-NO(2)-T and its metabolite, 2-nitrosotoluene (2-NO-T), using (32)P-5'-end-labeled DNA. We measured 8-oxo-7, 8-dihydro-2'-deoxyguanosine (8-oxodG), an indicator of oxidative DNA damage, in calf thymus DNA and cellular DNA in cultured human leukemia (HL-60) cells treated with 2-NO(2)-T and 2-NO-T. 8-Oxoguanine DNA glycosylase (OGG1) gene expression in HL-60 cells was measured by real-time polymerase chain reaction (PCR). We examined estrogenic activity using an E-screen assay and a surface plasmon resonance (SPR) sensor.

RESULTS

In experiments with isolated DNA fragments, 2-NO-T induced oxidative DNA damage in the presence of Cu (II) and β-nicotinamide adenine dinucleotide disodium salt (reduced form) (NADH), while 2-NO(2)-T did not. 2-NO-T significantly increased levels of 8-oxodG in HL-60 cells. Real-time polymerase chain reaction (PCR) analysis revealed upregulation of OGG1 gene expression induced by 2-NO-T. An E-screen assay using the human breast cancer cell line MCF-7 revealed that 2-NO(2)-T induced estrogen-dependent cell proliferation. In contrast, 2-NO-T decreased the cell number and suppressed 17β-estradiol-induced cell proliferation. The data obtained with the SPR sensor using estrogen receptor α and the estrogen response element supported the results of the E-screen assay.

CONCLUSIONS

Oxidative DNA damage caused by 2-NO-T and estrogen-disrupting effects caused by 2-NO(2)-T and 2-NO-T may play a role in the reproductive toxicity and carcinogenicity of these entities.

Urinary bladder carcinogenesis induced by chronic exposure to persistent low-dose ionizing radiation after Chernobyl accident

Urinary bladder urothelium as well as cells in the microenvironment of lamina propria (endothelial elements, fibroblasts and lymphocytes) demonstrate a number of responses to chronic persistent long-term, low-dose ionizing radiation (IR). Thus, oxidative stress occurs, accompanied by up-regulation of at least two signaling pathways (p38 mitogen-activated protein kinase and nuclear factor-kappaB cascades) and activation of growth factor receptors, in the bladder urothelium of people living in Cesium 137-contaminated areas of Ukraine, resulting in chronic inflammation and the development of proliferative atypical cystitis, so-called Chernobyl cystitis, which is considered a possible pre-neoplastic condition in humans. Furthermore, significant alterations in regulation of cell cycle transitions are associated with increased cell proliferation, along with up-regulated ubiquitination and sumoylation processes as well as inefficient DNA repair (base and nucleotide excision repair pathways) in the affected urothelium. The microenvironmental changes induced by chronic long-term, low-dose IR also appear to promote angiogenesis and remodeling of the extracellular matrix that could facilitate invasion as well as progression of pre-existing initiated cells to malignancy. Based on the available findings, new strategies have been developed for predicting and treatment of Chernobyl cystitis-a first step in urinary bladder carcinogenesis in humans.

Induction of mitosis delay, apoptosis and aneuploidy in human cells by phenyl hydroquinone, an Ames test-negative carcinogen

Ortho-phenyl phenol and its hepatic derivative, phenyl hydroquinone, do not generate base-substitution-type mutations, but cause bladder cancer in rats and mice. The mechanism of their carcinogenic effect is unknown. We have previously shown that o-phenyl phenol and phenyl hydroquinone induce mitotic arrest and aneuploidy in Saccharomyces cerevisiae. To further delineate the mechanism of action of phenyl hydroquinone, we examined its effect on human cells. Treatment of the colon cancer cell line HCT116 with 0 to 150 microM phenyl hydroquinone caused a concentration-dependent inhibition of growth, accumulation of cells having G2/M DNA content, and an increase in the mitotic index. Moreover, a dose-dependent increase in apoptotic cells was observed. Finally, a high frequency of aneuploid cells was found. On the other hand, no increase in gamma-H2AX foci was observed. The results show that phenyl hydroquinone does induce mitotic arrest, apoptosis and aneuploidy in the absence of DNA damage. Our results may be useful to understand the mechanisms of action of chemical substances that are Ames test-negative carcinogens.

Possible carcinogenic risks of copper gluconate and their prevention by co-administered green tea catechins evaluated by a rat medium-term multi-organ carcinogenicity bioassay protocol

Carcinogenic risks of copper gluconate, green tea catechins and their combined exposure were evaluated using a rat medium-term multi-organ carcinogenicity bioassay protocol. Male BrlHan:WIST@Jcl (GALAS) rats were given N-nitrosodiethylamine (DEN), N-methylnitrosourea (MNU), 1,2-dimethylhydrazine (DMH), N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) and 2,2'-dihydroxy-di-n-propylnitrosamine (DHPN) for a total multiple initiation period of 4 weeks (DMBDD treatment). Rats were then given a diet containing copper gluconate at a concentration of 0, 10, 300, 3000 or 6000 ppm with or without a co-administration of catechins starting 1 week later by admixing in the drinking water at a concentration of 5000 ppm. All survivors were sacrificed at the end of week 29. Number of putatively preneoplastic, glutathione S-transferase placental form-positive, liver lesions significantly increased by copper gluconate of 300 ppm or greater. In addition, both incidence and grade of hyperplasia in the forestomach significantly increased by copper gluconate of 6000 ppm. Catechins, exerting no effects by themselves, inhibited these effects of copper gluconate. The present results indicate that copper gluconate may possess carcinogenic risks for the liver and forestomach at its high dose level, and that co-administered green tea catechins may exert preventive effects.

Development of a new E. coli strain to detect oxidative mutation and its application to the fungicide o-phenylphenol and its metabolites

Oxidative mutation is mainly induced by reactive oxygen species (ROS), such as the superoxide anion radical (O(2)(-)) and hydrogen peroxide (H(2)O(2)). However, in Escherichia coli (E. coli), ROS are eliminated by enzymes such as superoxide dismutase and catalase, which are coded by sodAB and katEG genes. In this study, to detect mutagens that induce oxidative mutation, a mutant (WP2katEGsodAB) with katEG and sodAB deleted was constructed by gene manipulation of E. coli WP2. H(2)O(2) and menadione sodium bisulfite generated mutation in WP2katEGsodAB but not in WP2. o-Phenylphenol (OPP) and its metabolites (phenylhydroquinone (PHQ) and phenyl-1,4-benzoquinone (PBQ)), which had been shown to be negative in the Ames test but reported to be carcinogenic, induced mutation in WP2katEGsodAB but not in WP2. These results suggest that the new assay may be useful for the detection of oxidative mutagens.

Analysis of genotoxicity and the carcinogenic mode of action for ortho-phenylphenol

Ortho-phenylphenol (OPP) and its sodium salt (SOPP) are commercial products that have wide human exposure and have been shown in several studies to be rodent carcinogens. Genetic toxicology data were assessed in an attempt to understand the carcinogenic mode of action of OPP and SOPP. More than 130 studies were evaluated to determine if OPP, SOPP, or any of their enzymatic or nonenzymatic breakdown products react directly with DNA to induce mutation, changes in chromosome structure or number, DNA repair, or nonspecific DNA damage including strand breakage or covalent binding. The genotoxicity databases for OPP and SOPP are not only large but heterogeneous, requiring weight-of-evidence methods to arrive at a conclusion regarding their genotoxic properties and potential. Evidence derived from the available studies leads to the conclusion that study results showing OPP/SOPP directly interacting with DNA are equivocal. Clastogenicity was the most consistent type of genetic toxicity produced by OPP/SOPP (and their break-down products) and was consistently associated with other intracellular preneoplastic toxicity produced at super-threshold concentrations. The weight of evidence from the combined database supports the hypothesis that OPP/SOPP-induced DNA damage is a threshold-dependent response associated with target tissue toxicity, most likely induced by their breakdown products phenylhydroquinone and phenylbenzoquinone. It is possible that this threshold-dependent clastogenicity could contribute to the carcinogenic mode of action for OPP or SOPP.

Oxidative DNA damage induced by a hydroperoxide derivative of cyclophosphamide

Interstrand DNA cross-linking has been considered to be the primary action mechanism of cyclophosphamide (CP) and its hydroperoxide derivative, 4-hydroperoxycyclophosphamide (4-HC). To clarify the mechanism of anti-tumor effects by 4-HC, we investigated DNA damage in a human leukemia cell line, HL-60, and its H(2)O(2)-resistant clone HP100. Apoptosis DNA ladder formation was detected in HL-60 cells treated with 4-HC, whereas it was not observed in HP100 cells. 4-HC significantly increased 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) formation, a marker of oxidative DNA damage, in HL-60 cells. On the other hand, CP did not significantly induce 8-oxodG formation and apoptosis in HL-60 cells under the same conditions as did 4-HC. Using (32)P-labeled DNA fragments from the human p53 tumor suppressor gene, 4-HC was found to cause Cu(II)-mediated oxidative DNA damage, but CP did not. Catalase inhibited 4-HC-induced DNA damage, including 8-oxodG formation, suggesting the involvement of H(2)O(2). The generation of H(2)O(2) during 4-HC degradation was ascertained by procedures using scopoletin and potassium iodide. We conclude that, in addition to DNA cross-linking, oxidative DNA damage through H(2)O(2) generation may participate in the anti-tumor effects of 4-HC.

Continuous flow immunosensor for highly selective and real-time detection of sub-ppb levels of 2-hydroxybiphenyl by using surface plasmon resonance imaging

A biosensor based on surface plasmon resonance (SPR) is developed for the detection of 2-hydroxybiphenyl (HBP). A monoclonal antibody against HBP (abbreviated hereafter as HBP-mAb) is developed and used for the detection of HBP by competitive SPR-based immunoassay and enzyme linked immunosorbent assay (ELISA) methods. A novel HBP-hapten compound, HBP-bovine serum albumin conjugate (HBP-BSA), derived by binding several HBP units with BSA by an aliphatic chain spacer is used in the development of antibody and for the functionalization of immunoprobes. HBP-BSA linked to the Au surface of the SPR sensor chip undergoes inhibitive immunoreaction with HBP-mAb in the presence of free HBP. The SPR-based immunoassay provides a rapid determination (response time: approximately 20 min) of the concentration of HBP in the range of 0.1-1000 ppb (ng/ml). Regeneration of the sensor chip is gained by treating the antibody-anchored SPR sensor chip with a pepsin solution (100 ppm (microg/ml); pH 2.0) for few minutes. The SPR sensor chip is reusable for the detection of HBP for more than 20 cycles with average loss of 0.35% reactivity per regeneration step. HBP concentration is determined as low as 0.1 and 3 ppb using the SPR sensor and ELISA measurements, respectively. The developed SPR sensor for HBP is free from interference by coexisting benzo[a]pyrene (BaP), 2,4-dichlorophenoxyacetic acid (2,4-D) and benz[a]anthracene; SPR angle shift obtained to the flow of HBP is almost same irrespective to the presence or absence of a same concentration of these carcinogenic polycyclic aromatic hydrocarbons together. The SPR sensor for HBP is proved to be applicable in simultaneous detection of HBP and BaP in parallel with another SPR sensor for BaP.

O-phenylphenol and its sodium and potassium salts: a toxicological assessment

Ortho-phenylphenol (OPP) and its sodium (SOPP) and potassium (POPP) salts are used as fungicides and disinfectants. Due to the widespread use of especially OPP and SOPP, the potential for consumer exposure and some "critical" findings the toxicological database is quite extensive and complex. In experimental animals toxicity after single oral and dermal administration of these compounds is low. For the skin and mucous membranes, OPP has to be considered as irritating, and SOPP and POPP as corrosive. A large number of chronic toxicity and reproduction studies did not show any indication of oestrogen-like or other endocrine effects of OPP in the mammalian organism. No teratogenic effects were observed after the administration of OPP or SOPP in rats, mice, and rabbits. In two-generation studies in rats, OPP did not affect reproduction. The available data do not suggest a relevant potential for immunotoxic properties. The administration of high dietary concentrations of OPP to mice up to 2 years induced hepatocellular changes indicative of adaptations to metabolic demands, zonal degeneration, focal hepatocellular necrosis, and/or pigmentation of the liver. Only in male mice of one study, using a strain prone to develop hepatocellular tumors at high spontaneous incidences, the incidence of hepatocellular adenomas was increased. The incidence of hepatocellular carcinomas was not affected by treatment. The urothel of the urinary bladder (at very high doses also of the renal pelvis and the papilla) is the main target tissue after the repeated oral exposure of rats. The changes initially consist of increased mitosis, followed by simple epithelial hyperplasia, developing to a papillary and/or nodular form, later on to papillomas and transitional carcinomas. Crystals or stones in the bladder do not play a decisive role in this cascade. SOPP is more effective than OPP in this respect. Male rats are much more sensitive than females. In mice, hamsters, guinea pigs, and dogs, urothelial lesions do not develop even at very high oral dose levels. The findings in rats explain why there is a large genotoxicity/mutagenicity data base not only for OPP and SOPP but also for their metabolites on nearly all kinds of endpoints/targets. The weight of evidence suggests that genotoxicity of OPP/SOPP or their metabolites does not play a decisive role for the carcinogenicity at the urothel. Among them are lack of DNA binding of OPP to the rat bladder epithelium, the differences between OPP and SOPP, between male and female rats, between rats and mice (despite roughly comparable toxicokinetics), as well as the fact that tumors develop only at dose levels inducing hyperplasias. In addition, the strong dependence of the incidence and severity of the nonneoplastic and neoplastic bladder changes on urinary pH values (modified by feeding of ammonium chloride or sodium hydrogen carbonate) is consistent with the hypothesis of a nongenotoxic mode of action. Finally, there is no correlation between the urinary concentration of OPP or its metabolites and the incidence of hyperplasias/tumors in the urinary bladder. Both tumorigenic effects in rats and male mice are considered to represent high-dose, sex- and/or species-specific phenomena, based on nongenotoxic mechanisms of action and therefore allow the conclusion that the conventional margin of safety approaches are appropriate when assessing the risk of applications of OPP and its salts.

Oxidative DNA damage by a common metabolite of carcinogenic nitrofluorene and N-acetylaminofluorene

Both carcinogenic NF and AAF are metabolized to a common N-hydroxy metabolite, N-OH-AF. We investigated oxidative DNA damage by N-OH-AF, using (32)P-labeled human DNA fragments from the human p53 and p16 tumor-suppressor genes and the c-Ha-ras-1 protooncogene. N-OH-AF caused Cu(II)-mediated DNA damage, and endogenous reductant NADH markedly enhanced this process. Catalase and bathocuproine, a Cu(I)-specific chelator, decreased the DNA damage, suggesting the involvement of H(2)O(2) and Cu(I). N-OH-AF induced piperidine-labile lesions frequently at thymine and cytosine residues. With formamidopyrimidine-DNA glycosylase treatment, N-OH-AF induced cleavage at guanine residues, especially of the ACG sequence complementary to codon 273, a well-known hot spot of the p53 gene. N-OH-AF dose-dependently induced 8-oxodG formation in the presence of Cu(II) and NADH. Treatment with N-OH-AF increased amounts of 8-oxodG in HL-60 cells compared to the H(2)O(2)-resistant clone HP100, supporting the involvement of H(2)O(2). The present study demonstrates that the N-hydroxy metabolite of NF and AAF induces oxidative DNA damage through H(2)O(2) in both a cell-free system and cultured human cells. We conclude that oxidative DNA damage may play an important role in the carcinogenic process of NF and AAF in addition to previously reported DNA adduct formation.

Detection and characterization of DNA adducts formed from metabolites of the fungicide ortho-phenylphenol

The significance of DNA adduction in ortho-phenylphenol-induced carcinogenesis remains unclear. Establishing adduct structures may contribute to resolving this issue. The chemical structures of the DNA adduction products resulting from the in vitro reaction of phenylbenzoquinone, the putative ultimate carcinogenic metabolite of the fungicide/disinfectant ortho-phenylphenol, are reported here. Three isomeric adducts that resulted from reaction of deoxyguanosine were characterized by UV, LC-ESI-MS, and MS/MS, and 1D and 2D COSY-NMR spectroscopy. The proposed mechanism of product formation is nucleophilic attack by the deoxyguanosine exocyclic amine nitrogen on an electrophilic quinone carbon, followed by stabilization through enolization. Another nucleophilic attack forms a five-membered ring, which aromatizes by dehydration to form the final product. Adducts were also characterized from deoxyadenosine and deoxycytidine, although conversions were at least 10 times lower. Structures are also proposed for these products. Cell culture studies confirmed that HepG2 cells incubated with phenylbenzoquinone at concentrations associated with cytotoxicity form the same DNA adducts.

The role of metals in site-specific DNA damage with reference to carcinogenesis

We reviewed the mechanism of oxidative DNA damage with reference to metal carcinogenesis and metal-mediated chemical carcinogenesis. On the basis of the finding that chromium (VI) induced oxidative DNA damage in the presence of hydrogen peroxide (H2O2), we proposed the hypothesis that endogenous reactive oxygen species play a role in metal carcinogenesis. Since then, we have reported that various metal compounds, such as cobalt, nickel, and ferric nitrilotriacetate, directly cause site-specific DNA damage in the presence of H2O2. We also found that carcinogenic metals could cause DNA damage through indirect mechanisms. Certain nickel compounds induced oxidative DNA damage in rat lungs through inflammation. Endogenous metals, copper and iron, catalyzed ROS generation from various organic carcinogens, resulting in oxidative DNA damage. Polynuclear compounds, such as 4-aminobiphenyl and heterocyclic amines, appear to induce cancer mainly through DNA adduct formation, although their N-hydroxy and nitroso metabolites can also cause oxidative DNA damage. On the other hand, mononuclear compounds, such as benzene metabolites, caffeic acid, and o-toluidine, should express their carcionogenicity through oxidative DNA damage. Metabolites of certain carcinogens efficiently caused oxidative DNA damage by forming NADH-dependent redox cycles. These findings suggest that metal-mediated oxidative DNA damage plays important roles in chemical carcinogenesis.

Dose- and time-response studies of sodium o-phenylphenate urinary bladder carcinogenicity in rats

Dose- and time-response studies of urinary bladder carcinogenesis due to orally administered sodium o-phenylphenate (OPP-Na) were performed using 5-week-old male Fischer 344 rats given diets containing 0 (control), 2500, 5000, 10,000, 15,000 or 20,000 ppm OPP-Na for 104 weeks and fed basal diets until 112 weeks (experiment 1). In addition, rats received diets containing 20,000 ppm OPP-Na for 0 (control), 12, 24, 52 or 104 weeks and were killed at week 112 (experiment 2). In experiment 1, the transitional cell carcinoma (TCC) was the major tumor type in the urinary bladder, and the dose-response curve was steep with many tumors occurring at the high doses of 15,000 and 20,000 ppm. The virtually safe dose at a risk level of 10(-6) for TCCs and papillomas was estimated to be 144 ppm by the Weibull model, a high value similar to that for sodium saccharin. In experiment 2, a few TCCs developed after 24 weeks of treatment, but the time-response curve was also steep with the majority of lesions occurring after longer exposure periods. Based on the observed steepness in dose- and time-responses, any implied cancer risk of OPP-Na at the low doses of interest to man must be considered to be very small.

Protective effect of phytic acid on oxidative DNA damage with reference to cancer chemoprevention

Phytic acid (myo-inositol hexaphosphate) is one of the most promising cancer chemopreventive agents. We investigated the mechanism by which phytic acid expresses preventive action to cancer. Phytic acid inhibited the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine in cultured cells treated with an H2O2-generating system, although it did not scavenge H2O2. Site-specific DNA damage by H2O2 and Cu(II) at GG and GGG sequences was inhibited by phytic acid, but not by myo-inositol. Phytic acid alone did not cause DNA damage and thus, it should not act as a prooxidant. We conclude that phytic acid acts as an antioxidant to inhibit the generation of reactive oxygen species from H2O2 by chelating metals, resulting in chemoprevention of cancer.

Sequence-specific DNA damage induced by carcinogenic danthron and anthraquinone in the presence of Cu(II), cytochrome P450 reductase and NADPH

The mechanism of metal-mediated DNA damage by carcinogenic danthron (1,8-dihydroxyanthraquinone) and anthraquinone was investigated by the DNA sequencing technique using 32P-labeled human DNA fragments obtained from the human c-Ha-ras-1 protooncogene and the p53 tumor suppressor gene. Danthron caused DNA damage particularly at guanines in the 5'-GG-3', 5'-GGGG-3', 5'-GGGGG-3' sequences (damaged bases are underlined) in the presence of Cu(II), cytochrome P450 reductase and the NADPH-generating system. The DNA damage was inhibited by catalase and bathocuproine, suggesting the involvement of H2O2 and Cu(I). The formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine increased with increasing concentration of danthron. On the other hand, carcinogenic anthraquinone induced less oxidative DNA damage than danthron. Electron spin resonance study showed that the semiquinone radical could be produced by P450 reductase plus NADPH-mediated reduction of danthron, while little signal was observed with anthraquinone. These results suggest that danthron is much more likely to be reduced by P450 reductase and generate reactive oxygen species through the redox cycle, leading to more extensive Cu(II)-mediated DNA damage than anthraquinone. In the case of anthraquinone, its hydroxylated metabolites with similar reactivity to danthron may participate in DNA damage in vivo. We conclude that oxidative DNA damage by danthron and anthraquinone seems to be relevant for the expression of their carcinogenicity.

Mechanism of oxidative DNA damage induced by carcinogenic 4-aminobiphenyl

DNA adduct formation is thought to be a major cause of DNA damage by carcinogenic aromatic amines. We investigated the ability of an aromatic amine, 4-aminobiphenyl (4-ABP) and its N-hydroxy metabolite (4-ABP(NHOH)) to cause oxidative DNA damage, using (32)P-labeled human DNA fragments from the p53 tumor suppressor gene and the c-Ha-ras-1 protooncogene. 4-ABP(NHOH) was found to cause Cu(II)-mediated DNA damage, especially at thymine residues. Addition of the endogenous reductant NADH led to dramatic enhancement of this process. Catalase and bathocuproine, a Cu(I)-specific chelator, reduced the amount of DNA damage, suggesting the involvement of H(2)O(2) and Cu(I). 4-ABP(NHOH) dose-dependently induced 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation in the presence of Cu(ll) and NADH. 4-ABP(NHOH) conversion to nitrosobiphenyl, as measured by UV-visible spectroscopy, occurred rapidly in the presence of Cu(II), suggesting Cu(II)-mediated autoxidation. Increased amounts of 8-OHdG were found in HL-60 cells compared to the H(2)O(2)-resistant clone HP100 following 4-ABP(NHOH) treatment, further supporting the involvement of H(2)O(2). The present study demonstrates that an N-hydroxy derivative of 4-ABP induces oxidative DNA damage through H(2)O(2) in both a cell-free system and in cultured human cells. We conclude that, in addition to DNA adduct formation, oxidative DNA damage may play an important role in the carcinogenic process of 4-ABP.

Production of DNA strand breaks in vitro and reactive oxygen species in vitro and in HL-60 cells by PCB metabolites

PCBs are industrial chemicals that continue to contaminate our environment. They cause various toxic effects in animals and in exposed human populations. The mechanisms of toxicity, however, are not completely understood. PCBs are metabolized by cytochromes P450 to mono- and dihydroxylated compounds. Dihydroxy-PCBs can potentially be oxidized to the corresponding quinones. We hypothesized that reactive oxygen species (ROS) are produced by redox reactions of PCB metabolites. We tested several synthetic dihydroxy- and quinoid-PCBs with 1-3 chlorines for their potential to produce ROS in vitro and in HL-60 human leukemia cells, and DNA strand breaks in vitro. All dihydroxy-PCBs tested produced superoxide. The quinones generated superoxide only in the presence of GSH, probably during the autoxidation of the glutathione conjugates. We observed increased superoxide production with decreasing halogenation. Incubation of dihydroxy-PCBs or PCB quinones + GSH with plasmid DNA resulted in DNA strand break induction in the presence of Cu(II). Tests with various ROS scavengers indicated that hydroxyl radicals and singlet oxygen are likely involved in this strand break induction. Finally, dihydroxy- and quinoid PCBs also produced ROS in HL-60 cells in a dose- and time-dependent manner. We conclude that dihydroxylated PCBs, and PCB quinones after reaction with GSH, produce superoxide and other ROS both in vitro and in HL-60 cells, and oxidative DNA damage in the form of DNA strand breaks in vitro. The reactions seen in vitro and in cells may well be a predictor of the toxicity of PCBs in animals.

Metabolic activation of o-phenylphenol to a major cytotoxic metabolite, phenylhydroquinone: role of human CYP1A2 and rat CYP2C11/CYP2E1

1. The in vitro metabolic activation of o-phenylphenol has been evaluated as yielding a toxic metabolite, 2,5-dihydroxybiphenyl (phenylhydroquinone), by p-hydroxylation in liver microsomes of rat and human. The involvement of rat CYP2C11, CYP2E1 and human CYP1A2 in the p-hydroxylation of o-phenylphenol is suggested. 2. 2,3- and phenylhydroquinone, which induced DNA single-strand scission in the presence of 1 microM CuCl2, were the most cytotoxic chemicals examined to cultured mammalian cell lines among o-phenylphenol, m-phenylphenol, p-phenylphenol, 2,2'-, 4,4'-, 2,3- and phenylhydroquinone. 3. Rat and human liver microsomes catalysed the formation of phenylhydroquinone, but not 2,3-dihydroxybiphenyl, using o-phenylphenol as a substrate. A higher rate of metabolic activation of o-phenylphenol was observed with livers of the male than the female rats by 5.6- and 2.6-fold respectively. 4. Inhibitory antibodies against the male-specific CYP2C11 inhibited hepatic o-phenylphenol p-hydroxylation in the male F344 and Sprague-Dawley rat by > 70%. Liver microsomes from the isoniazid-treated rats produced 1.8- and 3-fold induction of o-phenylphenol p-hydroxylation and chlorzoxazone 6-hydroxylation (a CYP2E1-dependent activity) respectively. 5. Human CYP1A2, expressed by baculovirus-mediated cDNA expression systems, exhibited a remarkably higher capacity for o-phenylphenol p-hydroxylation at concentrations of 5 (> 5-fold), 50 (> 2-fold) and 500 microM (> 2-fold) than CYP2A, CYP2B, CYP2Cs, CYP2D6, CYP2E1 and CYP3A4 on the basis of pmol P450. 6. Among various CYP inhibitors tested here, 7,8-benzoflavone and furafylline, typical human CYP1A2 inhibitors, inhibited the microsomal p-hydroxylation of o-phenylphenol in human livers most potently by 70 and 50% respectively. 7. The results thus indicate the involvement of rat CYP2C11/CYP2E1 and human CYP1A2 in the hepatic p-hydroxylation of o-phenylphenol.

Increased oxidative stress with gene alteration in urinary bladder urothelium after the Chernobyl accident

We have previously shown that bladder urothelium of people living in the cesium-137 ((137)Cs)-contaminated areas of Ukraine demonstrates accumulation of stable p53 and p53 mutational inactivation, preferentially through G:C to A:T transition mutations at CpG dinucleotides, with a codon 245 hot spot. In the present study, we analyzed immuno-histochemically the relationship between oxidative stress markers and over-expression of p53 and H-ras in urinary bladder urothelium from 42 men with benign prostatic hyperplasia. Bladder mapping biopsies were obtained from 15 patients from a highly radiocontaminated area (group I), 14 patients from the less contaminated city of Kiev (group II) and 13 patients as a control group from "clean" (without radiocontamination) areas of Ukraine (group III). Irradiation cystitis with multiple foci of severe dysplasia and carcinoma in situ were observed in 15 of 15 (100%, group I) and 9 of 14 (64%, group II) cases, with 4 small transitional-cell carcinomas incidentally detected in groups I and II. Markedly elevated levels of inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2) and 8-hydroxy-2;-deoxyguanosine (8-OHdG) were noted in these bladder urothelial lesions from groups I and II, accompanied by strong over-expression of p53 and less H-ras expression. These findings support the hypothesis that iNOS, COX-2 and 8-OHdG in bladder urothelium are induced by long-term exposure to low-dose radiation with a close relationship to p53 over-expression that could predispose to bladder carcinogenesis.

Oxidative DNA damage by vitamin A and its derivative via superoxide generation

Recent intervention studies revealed that beta-carotene supplement to smokers resulted in a higher incidence of lung cancer. However, the causal mechanisms remain to be clarified. We reported here that vitamin A (retinol) and its derivative (retinal) caused cellular DNA cleavage detected by pulsed field gel electrophoresis. Retinol and retinal significantly induced 8-oxo-7,8-dihydro-2'-deoxyguanosine formation in HL-60 cells but not in H(2)O(2)-resistant HP100 cells, suggesting the involvement of H(2)O(2) in cellular DNA damage. Experiments using (32)P-labeled isolated DNA demonstrated that retinol and retinal caused Cu(II)-mediated DNA damage, which was inhibited by catalase. UV-visible spectroscopic and electron spin resonance-trapping studies revealed the generation of superoxide and carbon-centered radicals, respectively. The superoxide generation during autoxidation of retinoids was significantly correlated with the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine, although the yield of carbon-centered radicals was not necessarily related to the intensity of DNA damage. These findings suggest that superoxide generated by autoxidation of retinoids was dismutated to H(2)O(2), which was responsible for DNA damage in the presence of endogenous metals. Retinol and retinal have prooxidant abilities, which might lead to carcinogenesis of the supplements of beta-carotene.