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Abstract
Antioxidants are considered as the most promising chemopreventive agents against various human cancers. However, some antioxidants play paradoxical roles, acting as "double-edged sword." A primary property of effective and acceptable chemopreventive agents should be freedom from toxic effects in healthy population. Miscarriage of the intervention by beta-carotene made us realize the necessity for evaluation of safety before recommending use of antioxidant supplements for chemoprevention. We have evaluated the safety of antioxidants on the basis of reactivity with DNA. Our results revealed that phytic acid, luteolin, and retinoic acid did not cause DNA damage under the experimental condition. Furthermore, phytic acid inhibited the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine, an indicator of oxidative DNA damage, in cultured cells treated with a H(2)O(2)-generating system. Thus, it is expected that these chemopreventive agents can safely protect humans against cancer. On the other hand, some chemopreventive agents with prooxidant properties (alpha-tocopherol, quercetin, catechins, isothiocyanates, N-acetylcysteine) caused DNA damage via generation of reactive oxygen species in the presence of metal ions and endogenous reductants under some circumstances. Furthermore, other chemopreventive agents (beta-carotene, genistein, daidzein, propyl gallate, curcumin) exerted prooxidant properties after metabolic activation. Therefore, further studies on safety should be required when antioxidants are used for cancer prevention.
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Affiliation(s)
- Shosuke Kawanishi
- Department of Environmental and Molecular Medicine, Mie University Graduate School of Medicine, Mie, 514-8507, Japan.
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52
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Sakano K, Mizutani M, Murata M, Oikawa S, Hiraku Y, Kawanishi S. Procyanidin B2 has anti- and pro-oxidant effects on metal-mediated DNA damage. Free Radic Biol Med 2005; 39:1041-9. [PMID: 16198231 DOI: 10.1016/j.freeradbiomed.2005.05.024] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/17/2005] [Revised: 05/03/2005] [Accepted: 05/17/2005] [Indexed: 01/10/2023]
Abstract
Procyanidin B2 (epicatechin-(4beta-8)-epicatechin), which is present in grape seeds, apples, and cacao beans, has antioxidant properties. We investigated the mechanism of preventive action of procyanidin B2 against oxidative DNA damage in human cultured cells and isolated DNA. Procyanidin B2 inhibited the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in the human leukemia cell line HL-60 treated with an H2O2-generating system. In contrast, a high concentration of procyanidin B2 increased the formation of 8-oxodG in HL-60 cells. Experiments with calf thymus DNA also revealed that procyanidin B2 decreased 8-oxodG formation by Fe(II)/H2O2, whereas procyanidin B2 induced DNA damage in the presence of Cu(II), and H2O2 extensively enhanced it. An electron spin resonance spin trapping study utilizing 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO) demonstrated that procyanidin B2 decreased the signal of M4PO-OH from H2O2 and Fe(II), whereas procyanidin B2 enhanced the signal from H2O2 and Cu(II). As an antioxidant mechanism, UV-visible spectroscopy showed that procyanidin B2 chelated Fe(II) at equivalent concentrations. As a pro-oxidant property, we examined DNA damage induced by procyanidin B2, using 32P-labeled DNA fragments obtained from genes relevant to human cancer. Our results raise the possibility that procyanidin B2 exerts both antioxidant and pro-oxidant properties by interacting with H2O2 and metal ions.
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Affiliation(s)
- Katsuhisa Sakano
- Department of Environmental and Molecular Medicine, Mie University Graduate School of Medicine, Edobashi 2-174, Tsu, Mie 514-8507, Japan
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53
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Huang D, Ou B, Prior RL. The chemistry behind antioxidant capacity assays. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2005; 53:1841-56. [PMID: 15769103 DOI: 10.1021/jf030723c] [Citation(s) in RCA: 3136] [Impact Index Per Article: 165.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
This review summarizes the multifaceted aspects of antioxidants and the basic kinetic models of inhibited autoxidation and analyzes the chemical principles of antioxidant capacity assays. Depending upon the reactions involved, these assays can roughly be classified into two types: assays based on hydrogen atom transfer (HAT) reactions and assays based on electron transfer (ET). The majority of HAT-based assays apply a competitive reaction scheme, in which antioxidant and substrate compete for thermally generated peroxyl radicals through the decomposition of azo compounds. These assays include inhibition of induced low-density lipoprotein autoxidation, oxygen radical absorbance capacity (ORAC), total radical trapping antioxidant parameter (TRAP), and crocin bleaching assays. ET-based assays measure the capacity of an antioxidant in the reduction of an oxidant, which changes color when reduced. The degree of color change is correlated with the sample's antioxidant concentrations. ET-based assays include the total phenols assay by Folin-Ciocalteu reagent (FCR), Trolox equivalence antioxidant capacity (TEAC), ferric ion reducing antioxidant power (FRAP), "total antioxidant potential" assay using a Cu(II) complex as an oxidant, and DPPH. In addition, other assays intended to measure a sample's scavenging capacity of biologically relevant oxidants such as singlet oxygen, superoxide anion, peroxynitrite, and hydroxyl radical are also summarized. On the basis of this analysis, it is suggested that the total phenols assay by FCR be used to quantify an antioxidant's reducing capacity and the ORAC assay to quantify peroxyl radical scavenging capacity. To comprehensively study different aspects of antioxidants, validated and specific assays are needed in addition to these two commonly accepted assays.
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Affiliation(s)
- Dejian Huang
- Food Science and Technology Program, Department of Chemistry, National University of Singapore, Singapore 117543, Singapore.
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54
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Hirakawa K, Yoshida M, Nagatsu A, Mizukami H, Rana V, Rawat MSM, Oikawa S, Kawanishi S. Chemopreventive Action of Xanthone Derivatives on Photosensitized DNA Damage¶. Photochem Photobiol 2005. [DOI: 10.1562/2004-07-29-ra-252.1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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55
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Lee KM, Yeo M, Choue JS, Jin JH, Park SJ, Cheong JY, Lee KJ, Kim JH, Hahm KB. Protective mechanism of epigallocatechin-3-gallate against Helicobacter pylori-induced gastric epithelial cytotoxicity via the blockage of TLR-4 signaling. Helicobacter 2004; 9:632-42. [PMID: 15610077 DOI: 10.1111/j.1083-4389.2004.00281.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
BACKGROUND Helicobacter pylori infection leads to gastric mucosal damage by several mechanisms including the direct effect of virulence factors produced by H. pylori, propagation of inflammation, oxidative stress, DNA damage, and induction of apoptosis. (-)-Epigallocatechin-3-gallate (EGCG), one of the green tea catechins, is known to suppress H. pylori-induced gastritis through its antioxidative and antibacterial actions. In this study, we evaluated the protective mechanism of EGCG against H. pylori-induced cytotoxicity in gastric epithelial cells. MATERIALS AND METHODS MTT assays and dye exclusion assays were performed to analyze the effect of EGCG on the viability of gastric epithelial cells. The degree of DNA damage was evaluated by Comet assay and apoptotic DNA fragmentation assay. To investigate the effect of EGCG on H. pylori-induced toll-like receptor 4 (TLR-4) signaling, reverse transcription-polymerase chain reaction and Western blot analysis corresponding to glycosylated TLR-4 were carried out. Lipoxygenase metabolites were measured with reverse-phase, high-performance liquid chromatography. RESULTS EGCG pretreatment effectively rescued gastric mucosal cells from the H. pylori-induced apoptotic cell death and DNA damage, and administration of this catechin enhanced gastric epithelial cell proliferation. Helicobacter pylori infection stimulated the glycosylation of TLR-4, which initiates intracellular signaling in the infected host cell, but the pretreatment with EGCG completely blocked the TLR-4 glycosylation. The blockage of TLR-4 activation by EGCG resulted in inactivation of extracellular signal response kinase 1/2 and of nuclear factor-kappaB, the downstream molecules of TLR-4 signaling induced by H. pylori. This disturbance of H. pylori-induced host cell signaling by EGCG attenuated the synthesis of the proinflammatory mediator, hydroxyeicosatetraenoic acid. CONCLUSIONS EGCG pretreatment showed significant cytoprotective effects against H. pylori-induced gastric cytotoxicity via interference of the TLR-4 signaling induced by H. pylori. Thus, our result implies that continuous intakes of green tea could prevent the deleterious consequences of H. pylori infection.
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Affiliation(s)
- Kee-Myung Lee
- Genomic Research Center for Gastroenterology, Department of Gastroenterology, Ajou University School of Medicine, Suwon, Korea
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56
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Sakano K, Oikawa S, Hiraku Y, Kawanishi S. Oxidative DNA damage induced by a melatonin metabolite, 6-hydroxymelatonin, via a unique non-o-quinone type of redox cycle. Biochem Pharmacol 2004; 68:1869-78. [PMID: 15450952 DOI: 10.1016/j.bcp.2004.06.016] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2004] [Accepted: 06/18/2004] [Indexed: 12/16/2022]
Abstract
Melatonin, an indolic pineal hormone, is produced primarily at night in mammals and is important in controlling biological rhythms. Although melatonin is known to be effective as a free radical scavenger and has an anti-cancer effect, carcinogenic properties have also been reported. In relation to its carcinogenic potential, we have examined whether 6-hydroxymelatonin, a major melatonin metabolite, can induce DNA damage in the presence of metal ion using [32P]-5'-end-labeled DNA fragments obtained from genes relevant to human cancer. 6-Hydroxymelatonin induced site-specific DNA damage in the presence of Cu(II). Formamidopyrimidine-DNA glycosylase treatment induced cleavage sites mainly at G residues of the 5'-TG-3' sequence, whereas piperidine treatment induced cleavage sites at T mainly of 5'-TG-3'. Interestingly, 6-hydroxymelatonin strongly damaged G and C of the 5'-ACG-3' sequence complementary to codon 273 of the p53 gene. These results suggest that 6-hydroxymelatonin can cause double-base lesions. DNA damage was inhibited by both catalase and bathocuproine, Cu(I)-specific stabilizer, suggesting that reactive species derived from the reaction of H2O2 with Cu(I) participate in DNA damage. Cytochrome P450 reductase efficiently enhanced 6-hydroxymelatonin-induced oxidative DNA damage and oxygen consumption, suggesting the formation of redox cycle. It is noteworthy that 6-hydroxymelatonin can efficiently induce DNA damage via non-o-quinone type of redox cycle. Formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a characteristic oxidative DNA lesion, in calf thymus DNA was significantly increased by 6-hydroxymelatonin in the presence of Cu(II). Furthermore, 6-hydroxymelatonin significantly increased the formation of 8-oxodG in human leukemia cell line HL-60 but not in HP100, a hydrogen peroxide (H2O2)-resistant cell line derived from HL-60. The 6-hydroxymelatonin-induced 8-oxodG formation in HL-60 cells significantly decreased by the addition of bathocuproine or o-phenanthroline. Therefore, it is concluded that melatonin may exhibit carcinogenic potential through oxidative DNA damage by its metabolite.
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Affiliation(s)
- Katsuhisa Sakano
- Department of Environmental and Molecular Medicine, Mie University School of Medicine, Mie 5148507, Japan
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57
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Betanzos-Cabrera G, Ramírez FJ, Muñoz JL, Barrón BL, Maldonado R. Inactivation of HSV-2 by ascorbate–Cu(II) and its protecting evaluation in CF-1 mice against encephalitis. J Virol Methods 2004; 120:161-5. [PMID: 15288958 DOI: 10.1016/j.jviromet.2004.05.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2003] [Accepted: 05/04/2004] [Indexed: 11/19/2022]
Abstract
Ascorbate is an important antioxidant. However, in the presence of transition metals such as Cu(II) or Fe(III), it also has pro-oxidant capabilities. The effect of ascorbate-Cu(II) in the in vitro infection of herpes simplex virus type 2 (HSV-2) and its protecting effect in a murine model was investigated. HSV-2 was treated with different concentrations of ascorbate in the presence of Cu(II). A group of CF-1 mice were treated with the inactivated virus and other treated with maintenance medium containing only ascorbate-Cu(II). Weeks later, mice were challenged intranasally with infectious viruses. HSV-2 was completely inactivated by 2mM ascorbate plus 1mM Cu(II). Ascorbate or Cu(II) alone did not inactivate the virus. Compared with the control group, 60% of the immunized animals did not show any sign of encephalitis and survived the herpes virus infection, while a 7% survival rate was observed in the control group (P = 0.056). We concluded that the in vitro treatment of HSV-2 with ascorbate-Cu(II) is not only able to inactivate the virus, but also suggested that the viral particles induced a protective response against herpes encephalitis. This inactivation may provide an alternative method to develop new agents therapeutics.
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Affiliation(s)
- Gabriel Betanzos-Cabrera
- Area Académica de Nutrición, Instituto de Ciencias de la Salud, Universidad Autónoma del Estado de Hidalgo, Abasolo 600 Pachuca de Soto, Hidalgo 42000, Mexico.
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58
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Senesse P, Meance S, Cottet V, Faivre J, Boutron-Ruault MC. High Dietary Iron and Copper and Risk of Colorectal Cancer: A Case-Control Study in Burgundy, France. Nutr Cancer 2004; 49:66-71. [PMID: 15456637 DOI: 10.1207/s15327914nc4901_9] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
Several hypotheses have been proposed for colorectal carcinogenesis, including formation of free radicals. A case-control study compared nutrient intake in 171 colorectal cancer cases versus 309 general population controls, using a detailed face-to-face food history questionnaire. A food composition table enabled us to determine the mean composition of the diet in macro- and micronutrients. Dietary intakes were separately categorized into quartiles by gender. Logistic regression models were adjusted for age, sex, energy, exercise, and body mass index. High energy, copper, iron, and vitamin E intakes were associated with an overall increased risk of colorectal cancer. The odds ratios associated with the fourth quartile of intake were 2.3 (95% confidence interval, 1.3-4.0), 2.4 (1.3-4.6), 2.2 (1.1-4.7), and 1.8 (1.0-3.4) for energy, copper, iron, and vitamin E, respectively. There were no significant associations with dietary fiber, folate, calcium, or antioxidant vitamins other than vitamin E. These findings regarding iron and copper suggest that free radicals play an important role in colorectal carcinogenesis, while the findings regarding vitamin E are so far unexplained.
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Affiliation(s)
- Pierre Senesse
- Registre Bourguignon des Cancers Digestifs, Faculté de Médecine, Dijon cedex, France
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59
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McNeil JJ, Robman L, Tikellis G, Sinclair MI, McCarty CA, Taylor HR. Vitamin E supplementation and cataract: randomized controlled trial. Ophthalmology 2004; 111:75-84. [PMID: 14711717 DOI: 10.1016/j.ophtha.2003.04.009] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2002] [Accepted: 04/16/2003] [Indexed: 12/12/2022] Open
Abstract
OBJECTIVE To determine whether treatment with vitamin E (500 IU daily) reduces either the incidence or rate of progression of age-related cataracts. DESIGN A prospective, randomized, double-masked, placebo-controlled clinical trial entitled the Vitamin E, Cataract and Age-Related Maculopathy Trial. PARTICIPANTS Of 1906 screened volunteers, 1193 eligible subjects with early or no cataract, aged 55 to 80 years, were enrolled and followed up for 4 years. INTERVENTION Subjects were assigned randomly to receive either 500 IU of natural vitamin E in soybean oil encapsulated in gelatin or a placebo with an identical appearance. MAIN OUTCOME MEASURES The incidence and progression rates of age-related cataract were assessed annually with both clinical lens opacity gradings and computerized analysis of Scheimpflug and retroillumination digital lens images obtained with a Nidek EAS-1000 lens camera. The analysis was undertaken using data from the eye with the more advanced opacity for each type of cataract separately and for any cataract changes in each individual. RESULTS Overall, 87% of the study population completed the 4 years of follow-up, with 74% of the vitamin E group and 76% of the placebo group continuing on their randomized treatment allocation throughout this time. For cortical cataract, the 4-year cumulative incidence rate was 4.5% among those randomized to vitamin E and 4.8% among those randomized to placebo (P = 0.87). For nuclear cataract, the corresponding rates were 12.9% and 12.1% (P = 0.77). For posterior subcapsular cataract, the rates were 1.7% and 3.5% (P = 0.08), whereas for any of these forms of cataract, they were 17.1% and 16.7%, respectively. Progression of cortical cataract was seen in 16.7% of the vitamin E group and 18.4% of the placebo group (P = 0.76). Corresponding rates for nuclear cataract were 11.4% and 11.9% (P = 0.84), whereas those of any cataract were 16.5% and 16.7%, respectively. There was no difference in the rate of cataract extraction between the 2 groups (P = 0.87). Lens characteristics of the participants withdrawn from the randomized medications were not different from those who continued. CONCLUSIONS Vitamin E given for 4 years at a dose of 500 IU daily did not reduce the incidence of or progression of nuclear, cortical, or posterior subcapsular cataracts. These findings do not support the use of vitamin E to prevent the development or to slow the progression of age-related cataracts.
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Affiliation(s)
- John J McNeil
- Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia.
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60
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Furukawa A, Oikawa S, Murata M, Hiraku Y, Kawanishi S. (−)-Epigallocatechin gallate causes oxidative damage to isolated and cellular DNA. Biochem Pharmacol 2003; 66:1769-78. [PMID: 14563487 DOI: 10.1016/s0006-2952(03)00541-0] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Green tea catechins, especially (-)-epigallocatechin gallate (EGCG), are believed to mediate much of the cancer chemopreventive effects of tea. However, it was reported that green tea catechins enhanced colon carcinogenesis in rats. Experiments using 32P-labeled DNA fragments obtained from human cancer-related genes showed that catechins induced DNA damage in the presence of metals such as Cu(II) and Fe(III) complexes. In the presence of Fe(III)EDTA, the order of DNA damaging ability was EGCG approximately (-)-epigallocatechin>(-)-epicatechin gallate>>catechin. Catechins plus Fe(III)EDTA caused DNA damage at every nucleotide, most likely due to *OH generation from H(2)O(2). In the presence of Cu(II), the order was (-)-epigallocatechin>catechin>EGCG>(-)-epicatechin gallate. Cu(II)-mediated DNA damage by EGCG occurred most frequently at T and G residues, especially of 5'-TG-3' and GG sequences. Catalase and bathocuproine inhibited the Cu(II)-mediated DNA damage, suggesting the involvement of H(2)O(2) and Cu(I). In the presence of metal ions, increased amounts of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) were found in DNA treated with EGCG. Furthermore, EGCG increased amounts of 8-oxodG in HL-60 cells, but not in the H(2)O(2)-resistant clone HP100. When GSH was reduced by L-buthionine-[S, R]-sulfoximine, a low concentration of EGCG increased amounts of 8-oxodG in HL-60 cells, further supporting the involvement of H(2)O(2) in cellular DNA damage. It is concluded that EGCG can induce H(2)O(2) generation and subsequent damage to isolated and cellular DNA, and that oxidative DNA damage may mediate the potential carcinogenicity of EGCG.
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Affiliation(s)
- Ayako Furukawa
- Department of Environmental and Molecular Medicine, Mie University School of Medicine, Mie 514-8507, Japan
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61
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Ogawa K, Hiraku Y, Oikawa S, Murata M, Sugimura Y, Kawamura J, Kawanishi S. Molecular mechanisms of DNA damage induced by procarbazine in the presence of Cu(II). Mutat Res 2003; 539:145-55. [PMID: 12948823 DOI: 10.1016/s1383-5718(03)00157-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Procarbazine [N-isopropyl-alpha-(2-methylhydrazino)-p-toluamide], a hydrazine derivative, which has been shown to have effective antineoplastic activity, induces cancer in some experimental animals and humans. To clarify a new mechanism for its carcinogenic effect, we examined DNA damage induced by procarbazine in the presence of metal ion, using 32P-5'-end-labeled DNA fragments obtained from the human p53 tumor suppressor gene and the c-Ha-ras-1 protooncogene. Procarbazine plus Cu(II) induced piperidine-labile and formamidopyrimidine-DNA glycosylase-sensitive lesions at the 5'-ACG-3' sequence, complementary to a hotspot of the p53 gene, and the 5'-TG-3' sequence. Catalase partially inhibited DNA damage, suggesting that not only H(2)O(2) but also other reactive species are involved. Procarbazine plus Cu(II) significantly increased the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine, which was completely inhibited by calatase. Electron spin resonance spin-trapping experiments revealed that methyl radicals were generated from procarbazine and Cu(II). On the basis of these findings, it is considered that procarbazine causes DNA damage through non-enzymatic formation of the Cu(I)-hydroperoxo complex and methyl radicals. In conclusion, in addition to alkylation, oxidative DNA damage may play important roles in not only antitumor effects but also mutagenesis and carcinogenesis induced by procarbazine.
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Affiliation(s)
- Kazuhiko Ogawa
- Department of Environmental and Molecular Medicine, Mie University School of Medicine, Tsu, Mie 514-8507, Japan
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62
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Woźniak K, Blasiak J. In vitro genotoxicity of lead acetate: induction of single and double DNA strand breaks and DNA-protein cross-links. Mutat Res 2003; 535:127-39. [PMID: 12581530 DOI: 10.1016/s1383-5718(02)00295-4] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Lead is present in the natural and occupational environment and is reported to interact with DNA, but the mechanism of this interaction is not fully understood. Using the alkaline comet assay we showed that lead acetate at 1-100 microM induced DNA damage in isolated human lymphocytes measured the change in the comet tail length. At 1 and 10 microM we observed an increase in the tail length, whereas at 100 microM a decrease was seen. The former effect could follow from the induction of DNA strand breaks and/or alkali-labile sites (ALS), the latter from the formation of DNA-DNA and/or DNA-protein cross-links. No difference was observed between tail length for the alkaline and pH 12.1 versions of the assay, which indicates that strand breaks and not ALS are responsible for the tail length increase induced by lead. The neutral version of the test revealed that lead acetate induced DNA double-strand breaks at all concentrations tested. The presence of spin traps, 5,5-dimethyl-pyrroline N-oxide (DMPO) and N-tert-butyl-alpha-phenylnitrone (PBN) did not influence the level of DNA damage induced by lead. Post-treatment of the lead-damaged DNA (at 100 microM treatment concentration) by endonuclease III (Endo III) and formamidopyrimidine-DNA glycosylase (Fpg), enzymes recognizing oxidized DNA bases, as well as 3-methyladenine-DNA glycosylase II, an enzyme recognizing alkylated bases, gave rise to a significant increase in the extent of DNA damage. Proteinase K caused an increase in comet tail length, suggesting that lead acetate might cross-link DNA with nuclear proteins. Vitamin A, E, C, calcium chloride and zinc chloride acted synergistically on DNA damage evoked by lead. The results obtained suggest that lead acetate may induce single-strand breaks (SSB) and double-strand breaks (DSB) in DNA as well as DNA-protein cross-links. The participation of free radicals in DNA-damaging potential of lead is not important and it concerns other reactive species than could be trapped by DMPO or PBN.
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Affiliation(s)
- Katarzyna Woźniak
- Department of Molecular Genetics, University of Lodz, Banacha 12/16, 90-237, Lodz, Poland.
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63
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Sakano K, Kawanishi S. Metal-mediated DNA damage induced by curcumin in the presence of human cytochrome P450 isozymes. Arch Biochem Biophys 2002; 405:223-30. [PMID: 12220536 DOI: 10.1016/s0003-9861(02)00302-8] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Although curcumin is known to exhibit antitumor activity, carcinogenic properties have also been reported. To clarify the potentiality of carcinogenesis by curcumin, we have examined whether curcumin can induce DNA damage in the presence of cytochrome P450 (CYP) using [32P]-5(')-end-labeled DNA fragments obtained from genes relevant to human cancer. Curcumin treated with CYP 2D6, CYP1A1, or CYP1A2 induced DNA damage in the presence of Cu(II). CYP2D6-treated curcumin caused base damage, especially at 5(')-TG-3('), 5(')-GC-3('), and GG sequences. The DNA damage was inhibited by both catalase and bathocuproine, suggesting that reactive species derived from the reaction of H(2)O(2) with Cu(I) participate in DNA damage. Formation of 8-oxo-7,8-dihydro-2(')-deoxyguanosine was significantly increased by CYP2D6-treated curcumin in the presence of Cu(II). Time-of- flight mass spectrometry demonstrated that CYP2D6 catalyzed the conversion of curcumin to O-demethyl curcumin. Therefore, it is concluded that curcumin may exhibit carcinogenic potential through oxidative DNA damage by its metabolite.
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Affiliation(s)
- Katsuhisa Sakano
- Department of Hygiene, Mie University School of Medicine, Mie 514-8507, Japan
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Rietjens IMCM, Boersma MG, Haan LD, Spenkelink B, Awad HM, Cnubben NHP, van Zanden JJ, Woude HVD, Alink GM, Koeman JH. The pro-oxidant chemistry of the natural antioxidants vitamin C, vitamin E, carotenoids and flavonoids. ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 2002; 11:321-33. [PMID: 21782615 DOI: 10.1016/s1382-6689(02)00003-0] [Citation(s) in RCA: 218] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2001] [Revised: 12/17/2001] [Accepted: 12/19/2001] [Indexed: 05/25/2023]
Abstract
Natural antioxidants like vitamin C, vitamin E, carotenoids, and polyphenols like flavonoids, are at present generally considered to be beneficial components from fruit and vegetables. The anti-oxidative properties of these compounds are often claimed to be responsible for various beneficial health effects of these food ingredients. Together these studies provide the basis for the present rapidly increasing interest for the use of natural antioxidants as functional food ingredients and/or as food supplements. However, at higher doses or under certain conditions antioxidant-type functional food ingredients may exert toxic pro-oxidant activities. The present manuscript gives an overview of especially this pro-oxidative chemistry and toxicity of well-known natural antioxidants including vitamin C, vitamin E, carotenoids and flavonoids.
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Affiliation(s)
- Ivonne M C M Rietjens
- Division of Toxicology, Wageningen University, Tuinlaan 5, 6703 HE, Wageningen, The Netherlands; WU/TNO Center for Food Toxicology, P.O. Box 8000, 6700 EA, Wageningen, The Netherlands
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65
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Błasiak J, Gloc E, Woźniak K, Młynarski W, Stolarska M, Skórski T, Majsterek I. Genotoxicity of idarubicin and its modulation by vitamins C and E and amifostine. Chem Biol Interact 2002; 140:1-18. [PMID: 12044557 DOI: 10.1016/s0009-2797(02)00012-1] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Idarubicin is an anthracycline anticancer drug used in haematological malignancies. The main side effect of idarubicin is free-radicals based cardiotoxicity. Using the comet assay we showed that the drug at concentrations from the range 0.001 to 10 microM induced DNA damage in normal human lymphocytes, measured as the increase in percentage of DNA in the tail (% tail DNA). The effect was dose-dependent. Treated cells were able to recover within a 120-min incubation. Recognised cell protector, amifostine at 14 mM decreased the mean % tail DNA of the cells exposed to idarubicin at all tested concentrations of the drug. So did vitamin C at 10 microM, but vitamin E (alpha-tocopherol) at 50 microM increased the % tail DNA. Lymphocytes exposed to idarubicin and treated with endonuclease III, formamidopyrimidine-DNA glycosylase and 3-methyladenine-DNA glycosylase II, enzymes recognizing oxidized and alkylated bases, displayed greater extent of DNA damage than those not treated with these enzymes. Pretreatment of lymphocytes with nitrone spin traps, N-tert-butyl-alpha-phenylnitrone and alpha-(4-pyridil-1-oxide)-N-tert-butylnitrone decreased the extent of DNA damage evoked by idarubicin. To discuss the influence of vitamins and amifostine in cancer cells we used also murine pro-B lymphoid BaF3 transformed with BCR/ABL oncogene. These cells can be treated as model cells of human acute myelogenous leukemia. The response of these cells to vitamin E was quantitatively the same as human lymphocytes. However, vitamin C did not exert any effect on DNA damage and amifostine, in spite to normal lymphocytes, potentiated this effect. The results obtained suggest that reactive oxygen species, including free radicals, may be involved in the formation of DNA lesions induced by idarubicin. The drug can also methylate DNA bases. Our results indicate that not only cardiotoxicity but also genotoxicity and in consequence induction of secondary malignancies should be taken into account as diverse side effects of idarubicin. Amifostine may potentate DNA-damage effect of idarubicin in cancer cells and decrease this effect in normal cells. Vitamin C can be considered as protective agents against DNA damage in normal cells in persons receiving idarubicin-based chemotherapy, but the use of vitamin E cannot be recommended and at least needs further research.
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Affiliation(s)
- Janusz Błasiak
- Department of Molecular Genetics, University of Lodz, Banacha 12/16, Poland.
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66
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Woźniak K, Błasiak J. Free radicals-mediated induction of oxidized DNA bases and DNA-protein cross-links by nickel chloride. Mutat Res 2002; 514:233-43. [PMID: 11815261 DOI: 10.1016/s1383-5718(01)00344-8] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Using the comet assay, we showed that nickel chloride at 250-1000 microM induced DNA damage in human lymphocytes, measured as the change in comet tail moment, which increased with nickel concentration up to 500 microM and then decreased. Observed increase might follow from the induction of strand breaks or/and alkali-labile sites (ALS) by nickel, whereas decrease from its induction of DNA-DNA and/or DNA-protein cross-links. Proteinase K caused an increase in the tail moment, suggesting that nickel chloride at 1000 microM might cross-link DNA with nuclear proteins. Lymphocytes exposed to NiCl(2) and treated with enzymes recognizing oxidized and alkylated bases: endonuclease III (Endo III), formamidopyrimidine-DNA glycosylase (Fpg) and 3-methyladenine-DNA glycosylase II (AlkA), displayed greater extent of DNA damage than those not treated with these enzymes, indicating the induction of oxidized and alkylated bases by nickel. The incubation of lymphocytes with spin traps, 5,5-dimethyl-pyrroline N-oxide (DMPO) and PBN decreased the extent of DNA damage, which might follow from the production of free radicals by nickel. The pre-treatment with Vitamin C at 10 microM and Vitamin E at 25 microM decreased the tail moment of the cells exposed to NiCl(2) at the concentrations of the metal causing strand breaks or/and ALS. The results obtained suggest that free radicals may be involved in the formation of strand breaks or/and ALS in DNA as well as DNA-protein cross-links induced by NiCl(2). Nickel chloride can also alkylate DNA bases. Our results support thesis on multiple, free radicals-based genotoxicity pathways of nickel.
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Affiliation(s)
- Katarzyna Woźniak
- Department of Molecular Genetics, University of Lodz, Banacha 12/16, 90-237, Lodz, Poland.
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Midorikawa K, Murata M, Oikawa S, Hiraku Y, Kawanishi S. Protective effect of phytic acid on oxidative DNA damage with reference to cancer chemoprevention. Biochem Biophys Res Commun 2001; 288:552-7. [PMID: 11676478 DOI: 10.1006/bbrc.2001.5808] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
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.
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Affiliation(s)
- K Midorikawa
- Department of Hygiene, Mie University School of Medicine, Mie, 514-8507, Japan
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68
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Burkitt MJ. A critical overview of the chemistry of copper-dependent low density lipoprotein oxidation: roles of lipid hydroperoxides, alpha-tocopherol, thiols, and ceruloplasmin. Arch Biochem Biophys 2001; 394:117-35. [PMID: 11566034 DOI: 10.1006/abbi.2001.2509] [Citation(s) in RCA: 196] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The mechanisms by which low-density lipoprotein (LDL) particles undergo oxidative modification to an atherogenic form that is taken up by the macrophage scavenger-receptor pathway have been the subject of extensive research for almost two decades. The most common method for the initiation of LDL oxidation in vitro involves incubation with Cu(II) ions. Although various mechanisms have been proposed to explain the ability of Cu(II) to promote LDL modification, the precise reactions involved in initiating the process remain a matter of contention in the literature. This review provides a critical overview and evaluation of the current theories describing the interactions of copper with the LDL particle. Following discussion of the thermodynamics of reactions dependent upon the decomposition of preexisting lipid hydroperoxides, which are present in all crude LDL preparations, attention is turned to the more difficult (but perhaps more physiologically-relevant) system of the hydroperoxide-free LDL particle. In both systems, the key role of alpha-tocopherol is discussed. In addition to its protective, radical-scavenging action, alpha-tocopherol can also behave as a prooxidant via its reduction of Cu(II) to Cu(I). Generation of Cu(I) greatly facilitates the decomposition of lipid hydroperoxides to chain-carrying radicals, but the mechanisms by which the vitamin promotes LDL oxidation in the absence of preformed hydroperoxides remain more speculative. In addition to the so-called tocopherol-mediated peroxidation model, in which polyunsaturated fatty acid oxidation is initiated by the alpha-tocopheroxyl radical (generated during the reduction of Cu(II) by alpha-tocopherol), an evaluation of the role of the hydroxyl radical is provided. Important interactions between copper ions and thiols are also discussed, particularly in the context of cell-mediated LDL oxidation. Finally, the mechanisms by which ceruloplasmin, a copper-containing plasma protein, can bring about LDL modification are discussed. Improved understanding of the mechanisms of LDL oxidation by copper ions should facilitate the establishment of any physiological role of the metal in LDL modification. It will also assist in the interpretation of studies in which copper systems of LDL oxidation are used in vitro to evaluate potential antioxidants.
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Affiliation(s)
- M J Burkitt
- Gray Cancer Institute, Mount Vernon Hospital, Northwood, Middlesex, HA6 2JR, United Kingdom
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69
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Nocentini S, Guggiari M, Rouillard D, Surgis S. Exacerbating effect of vitamin E supplementation on DNA damage induced in cultured human normal fibroblasts by UVA radiation. Photochem Photobiol 2001; 73:370-7. [PMID: 11332032 DOI: 10.1562/0031-8655(2001)073<0370:eeoves>2.0.co;2] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The effects of vitamin E supplementation were evaluated in cultured human normal fibroblasts exposed to ultraviolet A radiation (320-380 nm) (UVA). Cells were incubated in medium containing alpha-tocopherol, alpha-tocopherol acetate or the synthetic analog Trolox for 24 h prior to UVA exposure. DNA damage in the form of frank breaks and alkali-labile sites, collectively termed single-strand breaks (SSB), was assayed by the technique of single cell gel electrophoresis (comet assay), immediately following irradiation or after different repair periods. The generation of hydrogen peroxide (H2O2) and superoxide ion (O2.-) was measured by flow cytometry through the oxidation of indicators into fluorescent dyes. It was observed that pretreatment of cells with any form of vitamin E resulted in an increased susceptibility to the photoinduction of DNA SSB and in a longer persistence of damage, whereas no significant change was observed in the production of H2O2 and O2.- reactive oxygen species, compared to untreated controls. These findings indicate that in human normal fibroblasts, exogenously added vitamin E exerts a promoting activity on DNA damage upon UVA irradiation and might lead to increased cytotoxic and mutagenic risks.
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Affiliation(s)
- S Nocentini
- UMR CNRS/Institut Curie 218, Institut Curie, Section de Recherche, 26 rue d'Ulm, 75248, Paris, France.
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70
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71
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Ito K, Kawanishi S. Sequence specificity of ultraviolet A-induced DNA damage in the presence of photosensitizer. Methods Enzymol 2000; 319:417-27. [PMID: 10907530 DOI: 10.1016/s0076-6879(00)19039-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
Affiliation(s)
- K Ito
- Department of Public Health, Kyoto University, Japan
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72
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Burkitt MJ, Duncan J. Effects of trans-resveratrol on copper-dependent hydroxyl-radical formation and DNA damage: evidence for hydroxyl-radical scavenging and a novel, glutathione-sparing mechanism of action. Arch Biochem Biophys 2000; 381:253-63. [PMID: 11032413 DOI: 10.1006/abbi.2000.1973] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is a natural product occurring in grapes and various other plants with medicinal properties. The phenolic antioxidant has been identified as a potential cancer chemopreventative agent and its presence in red wine has been suggested to be linked to the low incidence of heart disease in some regions of France. Recently, however, resveratrol was reported to promote DNA fragmentation in the presence of copper ions (K. Fukuhara and N. Miyata, 1998, Bioorg. Med. Chem. Lett. 8, 3187-3192), prompting us to investigate this phenomenon in mechanistic detail. By acting as a reducing agent, resveratrol was found to promote hydroxyl-radical (*OH) formation by DNA-bound Cu(H) ions. However, in the presence of either ascorbic acid or glutathione (i.e., under more physiological conditions), the phenolic lost this property and behaved as an antioxidant. In the ascorbate system, resveratrol had no effect on the rate of *OH formation, but protected DNA from damage by acting as a radical-scavenging antioxidant. In contrast, in the glutathione system, resveratrol inhibited *OH formation via a novel mechanism involving the inhibition of glutathione disulfide formation. We have concluded, therefore, that the DNA-damaging properties of resveratrol, identified recently by Fukuhara and Miyata, will be of no significance under physiological conditions. To the contrary, we have demonstrated that the phenolic behaves as a powerful antioxidant, both via classical, hydroxyl-radical scavenging and via a novel, glutathione-sparing mechanism.
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Affiliation(s)
- M J Burkitt
- Gray Laboratory Cancer Research Trust, Mount Vernon Hospital, Northwood, Middlesex, United Kingdom.
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Zhu BZ, Chevion M. Copper-mediated toxicity of 2,4,5-trichlorophenol: biphasic effect of the copper(I)-specific chelator neocuproine. Arch Biochem Biophys 2000; 380:267-73. [PMID: 10933881 DOI: 10.1006/abbi.2000.1919] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The lipophilic copper(I)-specific chelator neocuproine has been frequently used as an inhibitor of copper-mediated damage in biological systems. In this communication we report that the copper-mediated toxicity of 2,4,5-trichlorophenol is markedly potentiated by neocuproine at levels which are near-stoichiometric with respect to the copper concentration but is inhibited at higher concentrations. However, no potentiation was observed when neocuproine was substituted by bathocuproinedisulfonic acid, a negative charged ligand with essentially the same copper-binding characteristics as neocuproine. We found that the potentiation by neocuproine was due to the formation of a lipophilic copper complex, while the inhibition by bathocuproinedisulfonic acid was due to the formation of a hydrophilic one. Caution in the use of neocuproine to study copper-mediated toxicity is advised.
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Affiliation(s)
- B Z Zhu
- Department of Cellular Biochemistry, Hebrew University-Hadassah Schools of Medicine and Dental Medicine, Jerusalem, 91120, Israel.
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Murata M, Kawanishi S. Oxidative DNA damage by vitamin A and its derivative via superoxide generation. J Biol Chem 2000; 275:2003-8. [PMID: 10636903 DOI: 10.1074/jbc.275.3.2003] [Citation(s) in RCA: 145] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
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.
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Affiliation(s)
- M Murata
- Department of Hygiene, Mie University School of Medicine, Tsu, Mie, 514-8507, Japan
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Ohkuma Y, Kawanishi S. Oxidative DNA damage by a metabolite of carcinogenic and reproductive toxic nitrobenzene in the presence of NADH and Cu(II). Biochem Biophys Res Commun 1999; 257:555-60. [PMID: 10198250 DOI: 10.1006/bbrc.1999.0525] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The mechanism of DNA damage induced by metabolites of nitrobenzene was investigated in relation to the carcinogenicity and reproductive toxicity of nitrobenzene. Nitrosobenzene, a nitrobenzene metabolite, induced NADH plus Cu(II)-mediated DNA cleavage frequently at thymine and cytosine residues. Catalase and bathocuproine inhibited the DNA damage, suggesting the involvement of H2O2 and Cu(I). Typical free hydroxyl radical scavengers showed no inhibitory effects on DNA damage. Nitrosobenzene caused the formation of 8-oxo-7, 8-dihydro-2'-deoxyguanosine in calf thymus DNA in the presence of NADH and Cu(II). ESR spectroscopic study has confirmed that nitrosobenzene is reduced by NADH to the phenylhydronitroxide radical even in the absence of Cu(II). These results suggest that nitrosobenzene can be reduced non-enzymatically by NADH, and the redox cycle reaction resulted in oxidative DNA damage due to the copper-oxygen complex, derived from the reaction of Cu(I) with H2O2.
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Affiliation(s)
- Y Ohkuma
- Department of Hygiene, Mie University School of Medicine, Tsu, Mie, 514-8507, Japan
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Yamashita N, Tanemura H, Kawanishi S. Mechanism of oxidative DNA damage induced by quercetin in the presence of Cu(II). Mutat Res 1999; 425:107-15. [PMID: 10082921 DOI: 10.1016/s0027-5107(99)00029-9] [Citation(s) in RCA: 132] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Quercetin, one of flavonoids, has been reported to be carcinogenic. There have been no report concerning carcinogenicity of kaempferol and luteolin which have structure similar to quercetin. DNA damage was examined by using DNA fragments obtained from the human p53 tumor suppressor gene. Quercetin induced extensive DNA damage via reacting with Cu(II), but kaempferol and luteolin induced little DNA damage even in the presence of Cu(II). Excessive quercetin inhibited copper-dependent DNA damage induced by quercetin. Bathocuproine, a Cu(I)-specific chelator, catalase and methional inhibited the DNA damage by quercetin, whereas free hydroxyl radical scavengers did not. Site specificity of the DNA damage was thymine and cytosine residues. The site specificity and the inhibitory effects suggested that DNA-copper-oxygen complex rather than free hydroxyl radical induced the DNA damage. Formation of 8-oxodG by quercetin increased extensively in the presence of Cu(II), whereas 8-oxodG formation by kaempferol or luteolin increased only slightly. This study suggests a good relationship between carcinogenicity and oxidative DNA damage of three flavonoids. The mechanism of DNA damage by quercetin was discussed in relation to the safety in cancer chemoprevention by flavonoids.
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Affiliation(s)
- N Yamashita
- Department of Hygiene, Mie University School of Medicine, Tsu, Mie 514-8507, Japan
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