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Potent DNA Damage by Polyhalogenated Quinoid Carcinogens and H2O2 via a Metal-Independent and Intercalation-Enhanced Oxidation Mechanism
redox-active chemicals to produce 5hmC at the cellular level, representing a new process for epigenetic alterations induced by chemicals.
344 Mitochondrial Permeability Transition Promoted by the Reaction of Organotelluranes (IV) with Thiol Groups of Membrane Proteins 1
César Henrique Yokomizo , Felipe Samuel Pessoto1, Rodrigo L.O.R. Cunha2, and Iseli Lourenço Nantes2 1 2 Universidade Federal de São Paulo, Brazil, Universidade Federal do ABC, Brazil In this study, it was investigated the effect of four organotelluranes (IV) RT-07, named RT-07A, RT-07B, RT-07C and RT-07D on the bioenergetics of isolated rat liver mitochondria (RLM) and cells. In a dose-dependent manner, the studied 2+ organotelluranes promoted mitochondrial swelling that was Ca dependent and inhibited by cyclosporine A. These compounds also promoted aggregation of mitochondrial proteins and decrease of total mitochondrial protein thiol content. These effects characterize the opening of the classical mitochondrial permeability transition pore (MPTP). Despite the reactivity of the studied organotelluranes with mitochondrial protein thiol groups, these compounds did not promoted glutathione depletion. In smooth muscle cells, these compounds promoted loss of 2+ mitochondrial DY and apoptosis. In the absence of Ca , the organotelluranes also promoted loss of mitochondrial DY in RLM concomitant with respiratory control decrease due to increase of state 4 respiration rate. In these conditions, mitochondrial swelling was absent and thiol content was higher than in the presence of 2+ Ca . The differentiated effects observed in the presence and in 2+ the absence of Ca are probably caused by the exposure of specific reactive protein thiol groups in different conditions. Keywords: Liver mitochondria; Organotelluranes; Mitochondrial permeability transition; Cyclosporin A; Calcium; Protein Thiol Funding: FAPESP, CNPq and UNIFESP
doi:10.1016/j.freeradbiomed.2012.10.382
345 Non-Enzymatic Generation and Accumulation of Cellular 5-Hydroxymethylcytosine by Redox-Active Quinones 1
346 Potent DNA Damage by Polyhalogenated Quinoid Carcinogens and H2O2 via a Metal-Independent and Intercalation-Enhanced Oxidation Mechanism 1
Ben-Zhan Zhu and Hailin Wang1 1 Chinese Academy of Sciences, China Polyhalogenated quinones are a class of carcinogenic intermediates and new chlorination disinfection byproducts. We found recently that the highly reactive and Ɣ biologically/environmentally important hydroxyl radicals ( OH) can be produced by polyhalogenated quinones and H2O2 independent of transition metal ions. However, it is not clear whether this Ɣ unusual metal-independent OH producing system can induce potent oxidative DNA damage; and if so, what are the unique characteristics compared with the classic iron-mediated Fenton system. Here we show that tetrachloro-1,4-benzoquinone (TCBQ) and H2O2 can induce oxidative damage to both dG and dsDNA, as measured by the formation of the well-known biomarker 8oxodG (8-oxo-7,8-dihydro-2’-deoxyguanosine); but surprisingly, it was more potent to induce 8-oxodG formation in dsDNA than in dG. We found that this is probably due to the strong intercalating ability of TCBQ to dsDNA through the competitive displacement by the well-known DNA intercalating agents, which may lead to Ɣ the generation of OH more adjacent to DNA. Interestingly, the Ɣ metal-independent OH producing system was also found to be more potent than the classic iron-mediated Fenton system to induce 8-oxodG formation in dsDNA. This is the first report that polyhalogenated quinoid carcinogens and H2O2 can induce potent DNA damage via a metal-independent and intercalationenhanced oxidation mechanism, which may partly explain their potential genotoxicity, mutagenesis, and carcinogenesis.
doi:10.1016/j.freeradbiomed.2012.10.384
Ben-Zhan Zhu and Hailin Wang1 1 Chinese Academy of Sciences, China The recently identified sixth nuclear DNA base 5hydroxymethylcytosine (5hmC) is an important epigenetic marker and may be involved in DNA demethylation and pluripotency in mammals. Currently, the most commonly accepted mechanism for the generation of 5hmC is through enzymatic oxidation of 5methylcytosine (5mC) by ten-eleven translocation (TET) family proteins in mammalian cells. 5hmC has been detected in various tissues with a wide disparity in abundance. However, the conversion of 5mC to 5hmC by TET proteins has only been identified in several 5hmC-abundant mammalian cells and tissues. Here we show an unprecedented non-enzymatic pathway for cellular generation of 5hmC induced by redox-active quinones, which may cause 0.35% 5mC to be oxidized and dramatically change epigenome. Interestingly, the formation of 5hmC is persistent and accumulative, which is in contrast to 8-oxo-7,8dihydro-2’-deoxyguanosine, another well-known biomarker for oxidatively generated DNA damage. The mechanism is found to be due to the redox-cycling of quinones, leading to the production of high levels of reactive oxygen species, which in turn undergo intracellular labile iron-catalyzed conversion to highly reactive hydroxyl radicals, which directly oxidize 5mC to 5hmC. We propose that this might be a common non-enzymatic pathway for
S140
doi:10.1016/j.freeradbiomed.2012.10.383
347 Mechanism of Metal-Independent Oxidation of 5Methyl-2´-Deoxycytidine (5mdC) by Halogenated Quinoid Carcinogens and Hydrogen Peroxide 1
Ben-Zhan Zhu and Jie Shao1 1 Chinese Academy of Sciences, China Tetrachloro-1,4-benzoquinone (TCBQ) is one of the major genotoxic metabolites of wood preservative pentachlorophenol (PCP). Recently we found that TCBQ and H2O2 can produce the highly reactive and biologically/environmentally important hydroxyl Ɣ radical ( OH) independent of transition metal ions. However, it is not clear whether TCBQ and H2O2 can oxidize 5-methyl-2’deoxycytidine (5mdC) to its methyl oxidation products, and if so, what is the underlying molecular mechanism. We found that 5mdC could be oxidized to 5-hydroperoxymethyl-, 5hydroxymethyl-, and 5-formyl-2’-deoxycytidine by the combination of TCBQ and H2O2, but not by either of them alone. The formation of the three methyl oxidation products was markedly inhibited by Ɣ OH scavengers and under anaerobic condition. Analogous results were observed with other halogenated quinones and the classic Fenton system. Based on these data, we proposed that the oxidation of 5mdC by TCBQ/H2O2 might be through the
SFRBM 2012
344 Mitochondrial Permeability Transition Promoted by the Reaction of Organotelluranes (IV) with Thiol Groups of Membrane Proteins 1
César Henrique Yokomizo , Felipe Samuel Pessoto1, Rodrigo L.O.R. Cunha2, and Iseli Lourenço Nantes2 1 2 Universidade Federal de São Paulo, Brazil, Universidade Federal do ABC, Brazil In this study, it was investigated the effect of four organotelluranes (IV) RT-07, named RT-07A, RT-07B, RT-07C and RT-07D on the bioenergetics of isolated rat liver mitochondria (RLM) and cells. In a dose-dependent manner, the studied 2+ organotelluranes promoted mitochondrial swelling that was Ca dependent and inhibited by cyclosporine A. These compounds also promoted aggregation of mitochondrial proteins and decrease of total mitochondrial protein thiol content. These effects characterize the opening of the classical mitochondrial permeability transition pore (MPTP). Despite the reactivity of the studied organotelluranes with mitochondrial protein thiol groups, these compounds did not promoted glutathione depletion. In smooth muscle cells, these compounds promoted loss of 2+ mitochondrial DY and apoptosis. In the absence of Ca , the organotelluranes also promoted loss of mitochondrial DY in RLM concomitant with respiratory control decrease due to increase of state 4 respiration rate. In these conditions, mitochondrial swelling was absent and thiol content was higher than in the presence of 2+ Ca . The differentiated effects observed in the presence and in 2+ the absence of Ca are probably caused by the exposure of specific reactive protein thiol groups in different conditions. Keywords: Liver mitochondria; Organotelluranes; Mitochondrial permeability transition; Cyclosporin A; Calcium; Protein Thiol Funding: FAPESP, CNPq and UNIFESP
doi:10.1016/j.freeradbiomed.2012.10.382
345 Non-Enzymatic Generation and Accumulation of Cellular 5-Hydroxymethylcytosine by Redox-Active Quinones 1
346 Potent DNA Damage by Polyhalogenated Quinoid Carcinogens and H2O2 via a Metal-Independent and Intercalation-Enhanced Oxidation Mechanism 1
Ben-Zhan Zhu and Hailin Wang1 1 Chinese Academy of Sciences, China Polyhalogenated quinones are a class of carcinogenic intermediates and new chlorination disinfection byproducts. We found recently that the highly reactive and Ɣ biologically/environmentally important hydroxyl radicals ( OH) can be produced by polyhalogenated quinones and H2O2 independent of transition metal ions. However, it is not clear whether this Ɣ unusual metal-independent OH producing system can induce potent oxidative DNA damage; and if so, what are the unique characteristics compared with the classic iron-mediated Fenton system. Here we show that tetrachloro-1,4-benzoquinone (TCBQ) and H2O2 can induce oxidative damage to both dG and dsDNA, as measured by the formation of the well-known biomarker 8oxodG (8-oxo-7,8-dihydro-2’-deoxyguanosine); but surprisingly, it was more potent to induce 8-oxodG formation in dsDNA than in dG. We found that this is probably due to the strong intercalating ability of TCBQ to dsDNA through the competitive displacement by the well-known DNA intercalating agents, which may lead to Ɣ the generation of OH more adjacent to DNA. Interestingly, the Ɣ metal-independent OH producing system was also found to be more potent than the classic iron-mediated Fenton system to induce 8-oxodG formation in dsDNA. This is the first report that polyhalogenated quinoid carcinogens and H2O2 can induce potent DNA damage via a metal-independent and intercalationenhanced oxidation mechanism, which may partly explain their potential genotoxicity, mutagenesis, and carcinogenesis.
doi:10.1016/j.freeradbiomed.2012.10.384
Ben-Zhan Zhu and Hailin Wang1 1 Chinese Academy of Sciences, China The recently identified sixth nuclear DNA base 5hydroxymethylcytosine (5hmC) is an important epigenetic marker and may be involved in DNA demethylation and pluripotency in mammals. Currently, the most commonly accepted mechanism for the generation of 5hmC is through enzymatic oxidation of 5methylcytosine (5mC) by ten-eleven translocation (TET) family proteins in mammalian cells. 5hmC has been detected in various tissues with a wide disparity in abundance. However, the conversion of 5mC to 5hmC by TET proteins has only been identified in several 5hmC-abundant mammalian cells and tissues. Here we show an unprecedented non-enzymatic pathway for cellular generation of 5hmC induced by redox-active quinones, which may cause 0.35% 5mC to be oxidized and dramatically change epigenome. Interestingly, the formation of 5hmC is persistent and accumulative, which is in contrast to 8-oxo-7,8dihydro-2’-deoxyguanosine, another well-known biomarker for oxidatively generated DNA damage. The mechanism is found to be due to the redox-cycling of quinones, leading to the production of high levels of reactive oxygen species, which in turn undergo intracellular labile iron-catalyzed conversion to highly reactive hydroxyl radicals, which directly oxidize 5mC to 5hmC. We propose that this might be a common non-enzymatic pathway for
S140
doi:10.1016/j.freeradbiomed.2012.10.383
347 Mechanism of Metal-Independent Oxidation of 5Methyl-2´-Deoxycytidine (5mdC) by Halogenated Quinoid Carcinogens and Hydrogen Peroxide 1
Ben-Zhan Zhu and Jie Shao1 1 Chinese Academy of Sciences, China Tetrachloro-1,4-benzoquinone (TCBQ) is one of the major genotoxic metabolites of wood preservative pentachlorophenol (PCP). Recently we found that TCBQ and H2O2 can produce the highly reactive and biologically/environmentally important hydroxyl Ɣ radical ( OH) independent of transition metal ions. However, it is not clear whether TCBQ and H2O2 can oxidize 5-methyl-2’deoxycytidine (5mdC) to its methyl oxidation products, and if so, what is the underlying molecular mechanism. We found that 5mdC could be oxidized to 5-hydroperoxymethyl-, 5hydroxymethyl-, and 5-formyl-2’-deoxycytidine by the combination of TCBQ and H2O2, but not by either of them alone. The formation of the three methyl oxidation products was markedly inhibited by Ɣ OH scavengers and under anaerobic condition. Analogous results were observed with other halogenated quinones and the classic Fenton system. Based on these data, we proposed that the oxidation of 5mdC by TCBQ/H2O2 might be through the
SFRBM 2012