The Experts below are selected from a list of 159 Experts worldwide ranked by ideXlab platform
Clement E. Furlong - One of the best experts on this subject based on the ideXlab platform.
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Paraoxonase (PON1), detoxification of nerve agents, and modulation of their toxicity
Handbook of Toxicology of Chemical Warfare Agents, 2020Co-Authors: Lucio G. Costa, Toby B. Cole, Jacqueline M. Garrick, Judit Marsillach, Clement E. FurlongAbstract:Abstract Paraoxonase (PON1) is a serum and liver enzyme that can hydrolyze in vitro several organophosphorus (OP) compounds, including the active metabolites of specific OP insecticides, and certain OP nerve agents such as sarin and soman. PON1 presents several genetic polymorphisms that influence its ability to hydrolyze OPs as well as its level of expression. Studies in animals, including transgenic mice, have shown that PON1 modulates the in vivo acute toxicity of certain OPs, such as chlorpyrifos oxon and Diazoxon. In contrast, because of its low catalytic efficiency toward paraoxon, PON1 does not influence the acute toxicity of this OP in vivo. The catalytic efficiency of PON1 toward nerve agents is similarly low, though some studies have shown that administration of exogenous PON1 can protect against the toxicity of soman and sarin. For use as catalytic bioscavengers, recombinant engineered PON1s need to be developed with an enhanced catalytic efficiency toward nerve agents being devoid of immunogenicity. Such PON1s would be excellent candidates for prophylactic and therapeutic applications in the case of OP nerve agent poisoning. A parallel strategy would be that of identifying and studying agents which would increase levels of endogenous PON1.
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Paraoxonase 1 (PON1) as a genetic determinant of susceptibility to organophosphate toxicity
Toxicology, 2012Co-Authors: Lucio G. Costa, Gennaro Giordano, Toby B. Cole, Judit Marsillach, Clement E. FurlongAbstract:a b s t r a c t Paraoxonase (PON1) is an A-esterase capable of hydrolyzing the active metabolites (oxons) of a number of organophosphorus (OP) insecticides such as parathion, diazinon and chlorpyrifos. PON1 activity is highest in liver and in plasma. Human PON1 displays two polymorphisms in the coding region (Q192R and L55M) and several polymorphisms in the promoter and the 3 � -UTR regions. The Q192R polymorphism imparts differential catalytic activity toward some OP substrates, while the polymorphism at position −108 (C/T) is the major contributor of differences in the levels of PON1 expression. Both contribute to determining an individual's PON1 "status". Animal studies have shown that PON1 is an important determinant of OP toxicity. Administration of exogenous PON1 to rats or mice protects them from the toxicity of specific OPs. PON1 knockout mice display a high sensitivity to the toxicity of Diazoxon and chlorpyrifos oxon, but not of paraoxon. In vitro catalytic efficiencies of purified PON192 alloforms for hydrolysis of specific oxon substrates accurately predict the degree of in vivo protection afforded by each isoform. Evidence is slowly emerging that a low PON1 status may increase susceptibility to OP toxicity in humans. Low PON1 activity may also contribute to the developmental toxicity and neurotoxicity of OPs, as shown by animal and human studies. © 2012 Published by Elsevier Ireland Ltd.
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paraoxonase 1 status as a risk factor for disease or exposure
Advances in Experimental Medicine and Biology, 2010Co-Authors: Rebecca J Richter, Gail P Jarvik, Clement E. FurlongAbstract:Human paraoxonase 1 (PON1) has broad substrate specificity and has been shown to protect against exposure to some organophosphorus (OP) insecticides due to its ability to hydrolyze toxic metabolites of some organophosphorothioate insecticides. PON1 status has been shown to be important in protecting against vascular disease, presumably due to the not-as-yet fully characterized role of the three PON proteins in modulating oxidative stress. More recently, all three PONs (1, 2, and 3) have been shown to inactivate the quorum sensing factor N-(3-oxododecanoyl)-l-homoserine lactone (3OC12-HSL) of Pseudomonas. Expression of human PON1 in Drosophila demonstrated the importance of PON1 in resistance to Pseudomonas infection. Many studies have examined only DNA single nucleotide polymorphisms as possible risk factors for disease or exposures. For all of the known functions of PON1, the level of PON1 enzyme is important and, in some cases, also the Q192R polymorphism. A simple high throughput two-substrate assay/analysis, plotting rates of Diazoxon hydrolysis vs. paraoxon hydrolysis, provided both PON1 levels and functional Q192R phenotype/genotype. We have developed a new two-substrate assay/analysis protocol that provides PON1 status without use of toxic OP substrates. Factors were determined for inter-converting rates of hydrolysis of different substrates.
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Paraoxonase 1 (PON1) status and substrate hydrolysis
Toxicology and applied pharmacology, 2008Co-Authors: Rebecca J Richter, Gail P Jarvik, Clement E. FurlongAbstract:Paraoxonase 1 (PON1) hydrolyzes a number of organophosphorus (OP) compounds including insecticides and nerve agents. The in vivo efficacy of PON1 to protect against a specific OP exposure depends on the catalytic efficiency of hydrolysis. The Q192R polymorphism affects the catalytic efficiency of hydrolysis of some substrates and not others. While PON1R192 hydrolyzes paraoxon approximately 9-times as efficiently as PON1Q192, the efficiency is insufficient to provide in vivo protection against paraoxon/parathion exposure. The two PON1192 alloforms have nearly equivalent but higher catalytic efficiencies for hydrolyzing Diazoxon (DZO) and provide equivalent in vivo protection against DZO exposures. On the other hand, PON1R192 is significantly more efficient in hydrolyzing chlorpyrifos oxon (CPO) than PON1Q192 and provides better protection against CPO exposure. Thus, for some exposures it is only the level of plasma PON1 that is important, whereas for others it is both plasma level and the PON1192 alloform(s) present in plasma that are important. In no case is the plasma level of PON1 unimportant, provided that the catalytic efficiency is sufficient to protect against the exposure. Two-substrate enzyme assay/analysis protocols that reveal both PON1 plasma levels and PON1192 phenotype (QQ; QR; RR) are designed to optimize the separation of PON1192 phenotypes; however, they have not been optimized for evaluating in vivo rates of OP detoxication. This study describes the adaptation of a non-OP, two-substrate determination of PON1 status to the conversion of the PON1 status data to physiologically relevant rates of DZO and CPO detoxication. Conversion factors were generated for rates of hydrolysis of different substrates.
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genetic variability in the cytochrome p450 paraoxonase 1 pon1 pathway for detoxication of organophosphorus compounds
Journal of Biochemical and Molecular Toxicology, 2007Co-Authors: Clement E. FurlongAbstract:Detoxication of organophosphorus (OP) compounds is affected by genetic and environmental modulation of a number of enzymes involved in the process. For organophosphorothioate insecticides, different P450 isozymes and variants carry out two reactions that have quite different consequences; (1) they bioactivate their parent compounds to highly toxic oxon forms that are many times more toxic than the parent compounds, and (2) concurrently, they dearylate the parent OP compounds, generating much less toxic metabolites. The ratios at which these different P450s carry out bioactivation versus dearylation differ among the P450 isozymes. The detoxication of the oxon forms of diazinon and chlorpyrifos is achieved by hydrolysis to the respective aromatic alcohols and diethyl phosphates primarily by paraoxonase 1 (PON1), a plasma enzyme tightly associated with high-density lipoprotein particles and also found in liver. Stoichiometric binding to other targets also contributes to the detoxication of these oxons. PON1 is polymorphically distributed in human populations with an amino acid substitution (Gln/Arg) at position 192 of this 354-amino acid protein (the initiator Met residue is cleaved on maturation) that determines the catalytic efficiency of hydrolysis of some substrates. In addition to the variable catalytic efficiency determined by the position 192 amino acid, protein levels of PON1 vary by as much as 15-fold among individuals with the same PON1192 genotype (Q/Q; Q/R; R/R). The generation of PON1 null mice and transgenic mice, expressing each of the human PON1192 alloforms in place of mouse PON1, has allowed for the examination of the physiological function of the PON1192 alloforms in OP detoxication. Sensitivity to Diazoxon exposure is primarily determined by the plasma level of PON1, whereas for chlorpyrifos oxon exposure, both the plasma PON1 level and the position 192 amino acid are important—PON1R192 is more efficient in inactivating chlorpyrifos oxon than is PON1Q192. The availability of PON1 null mice provides an opportunity to examine the contribution of other enzymes in the OP detoxication pathways without PON1 interference. © 2007 Wiley Periodicals, Inc. J Biochem Mol Toxicol 21:197–205, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20181
John M. Dickenson - One of the best experts on this subject based on the ideXlab platform.
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phenyl saligenin phosphate induced caspase 3 and c jun n terminal kinase activation in cardiomyocyte like cells
Chemical Research in Toxicology, 2015Co-Authors: Shatha G. Felemban, Alan J. Hargreaves, Fathi A. Smida, David J. Boocock, A C Garner, John M. DickensonAbstract:At present, little is known about the effect(s) of organophosphorous compounds (OPs) on cardiomyocytes. In this study, we have investigated the effects of phenyl saligenin phosphate (PSP), two organophosphorothioate insecticides (diazinon and chlorpyrifos), and their acutely toxic metabolites (Diazoxon and chlorpyrifos oxon) on mitotic and differentiated H9c2 cardiomyoblasts. OP-induced cytotoxicity was assessed by monitoring MTT reduction, LDH release, and caspase-3 activity. Cytotoxicity was not observed with diazinon, Diazoxon, or chlorpyrifos oxon (48 h exposure; 200 μM). Chlorpyrifos-induced cytotoxicity was only evident at concentrations >100 μM. In marked contrast, PSP displayed pronounced cytotoxicity toward mitotic and differentiated H9c2 cells. PSP triggered the activation of JNK1/2 but not ERK1/2, p38 MAPK, or PKB, suggesting a role for this pro-apoptotic protein kinase in PSP-induced cell death. The JNK1/2 inhibitor SP 600125 attenuated PSP-induced caspase-3 and JNK1/2 activation, confirming the role of JNK1/2 in PSP-induced cytotoxicity. Fluorescently labeled PSP (dansylated PSP) was used to identify novel PSP binding proteins. Dansylated PSP displayed cytotoxicity toward differentiated H9c2 cells. 2D-gel electrophoresis profiles of cells treated with dansylated PSP (25 μM) were used to identify proteins fluorescently labeled with dansylated PSP. Proteomic analysis identified tropomyosin, heat shock protein β-1, and nucleolar protein 58 as novel protein targets for PSP. In summary, PSP triggers cytotoxicity in differentiated H9c2 cardiomyoblasts via JNK1/2-mediated activation of caspase-3. Further studies are required to investigate whether the identified novel protein targets of PSP play a role in the cytotoxicity of this OP, which is usually associated with the development of OP-induced delayed neuropathy.
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Phenyl Saligenin Phosphate Induced Caspase‑3 and c‑Jun N‑Terminal Kinase Activation in Cardiomyocyte-Like Cells
2015Co-Authors: Shatha G. Felemban, Alan J. Hargreaves, Christopher A. Garner, Fathi A. Smida, David J. Boocock, John M. DickensonAbstract:At present, little is known about the effect(s) of organophosphorous compounds (OPs) on cardiomyocytes. In this study, we have investigated the effects of phenyl saligenin phosphate (PSP), two organophosphorothioate insecticides (diazinon and chlorpyrifos), and their acutely toxic metabolites (Diazoxon and chlorpyrifos oxon) on mitotic and differentiated H9c2 cardiomyoblasts. OP-induced cytotoxicity was assessed by monitoring MTT reduction, LDH release, and caspase-3 activity. Cytotoxicity was not observed with diazinon, Diazoxon, or chlorpyrifos oxon (48 h exposure; 200 μM). Chlorpyrifos-induced cytotoxicity was only evident at concentrations >100 μM. In marked contrast, PSP displayed pronounced cytotoxicity toward mitotic and differentiated H9c2 cells. PSP triggered the activation of JNK1/2 but not ERK1/2, p38 MAPK, or PKB, suggesting a role for this pro-apoptotic protein kinase in PSP-induced cell death. The JNK1/2 inhibitor SP 600125 attenuated PSP-induced caspase-3 and JNK1/2 activation, confirming the role of JNK1/2 in PSP-induced cytotoxicity. Fluorescently labeled PSP (dansylated PSP) was used to identify novel PSP binding proteins. Dansylated PSP displayed cytotoxicity toward differentiated H9c2 cells. 2D-gel electrophoresis profiles of cells treated with dansylated PSP (25 μM) were used to identify proteins fluorescently labeled with dansylated PSP. Proteomic analysis identified tropomyosin, heat shock protein β-1, and nucleolar protein 58 as novel protein targets for PSP. In summary, PSP triggers cytotoxicity in differentiated H9c2 cardiomyoblasts via JNK1/2-mediated activation of caspase-3. Further studies are required to investigate whether the identified novel protein targets of PSP play a role in the cytotoxicity of this OP, which is usually associated with the development of OP-induced delayed neuropathy
Rebecca J Richter - One of the best experts on this subject based on the ideXlab platform.
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paraoxonase 1 status as a risk factor for disease or exposure
Advances in Experimental Medicine and Biology, 2010Co-Authors: Rebecca J Richter, Gail P Jarvik, Clement E. FurlongAbstract:Human paraoxonase 1 (PON1) has broad substrate specificity and has been shown to protect against exposure to some organophosphorus (OP) insecticides due to its ability to hydrolyze toxic metabolites of some organophosphorothioate insecticides. PON1 status has been shown to be important in protecting against vascular disease, presumably due to the not-as-yet fully characterized role of the three PON proteins in modulating oxidative stress. More recently, all three PONs (1, 2, and 3) have been shown to inactivate the quorum sensing factor N-(3-oxododecanoyl)-l-homoserine lactone (3OC12-HSL) of Pseudomonas. Expression of human PON1 in Drosophila demonstrated the importance of PON1 in resistance to Pseudomonas infection. Many studies have examined only DNA single nucleotide polymorphisms as possible risk factors for disease or exposures. For all of the known functions of PON1, the level of PON1 enzyme is important and, in some cases, also the Q192R polymorphism. A simple high throughput two-substrate assay/analysis, plotting rates of Diazoxon hydrolysis vs. paraoxon hydrolysis, provided both PON1 levels and functional Q192R phenotype/genotype. We have developed a new two-substrate assay/analysis protocol that provides PON1 status without use of toxic OP substrates. Factors were determined for inter-converting rates of hydrolysis of different substrates.
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Paraoxonase 1 (PON1) status and substrate hydrolysis
Toxicology and applied pharmacology, 2008Co-Authors: Rebecca J Richter, Gail P Jarvik, Clement E. FurlongAbstract:Paraoxonase 1 (PON1) hydrolyzes a number of organophosphorus (OP) compounds including insecticides and nerve agents. The in vivo efficacy of PON1 to protect against a specific OP exposure depends on the catalytic efficiency of hydrolysis. The Q192R polymorphism affects the catalytic efficiency of hydrolysis of some substrates and not others. While PON1R192 hydrolyzes paraoxon approximately 9-times as efficiently as PON1Q192, the efficiency is insufficient to provide in vivo protection against paraoxon/parathion exposure. The two PON1192 alloforms have nearly equivalent but higher catalytic efficiencies for hydrolyzing Diazoxon (DZO) and provide equivalent in vivo protection against DZO exposures. On the other hand, PON1R192 is significantly more efficient in hydrolyzing chlorpyrifos oxon (CPO) than PON1Q192 and provides better protection against CPO exposure. Thus, for some exposures it is only the level of plasma PON1 that is important, whereas for others it is both plasma level and the PON1192 alloform(s) present in plasma that are important. In no case is the plasma level of PON1 unimportant, provided that the catalytic efficiency is sufficient to protect against the exposure. Two-substrate enzyme assay/analysis protocols that reveal both PON1 plasma levels and PON1192 phenotype (QQ; QR; RR) are designed to optimize the separation of PON1192 phenotypes; however, they have not been optimized for evaluating in vivo rates of OP detoxication. This study describes the adaptation of a non-OP, two-substrate determination of PON1 status to the conversion of the PON1 status data to physiologically relevant rates of DZO and CPO detoxication. Conversion factors were generated for rates of hydrolysis of different substrates.
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pon1 status of farmworker mothers and children as a predictor of organophosphate sensitivity
Pharmacogenetics and Genomics, 2006Co-Authors: Clement E. Furlong, Rebecca J Richter, Nina Holland, Asa Bradman, Brenda EskenaziAbstract:The objective was to determine PON1 status as a predictor for organophosphorus insecticide sensitivity in a cohort of Latina mothers and newborns from the Salinas Valley, California, an area with high levels of organophosphorus insecticide use. PON1 status was established for 130 pregnant Latina women and their newborns using a high-throughput two substrate activity/analysis method which plots rates of Diazoxon (DZO) hydrolysis against rates of paraoxon (PO) hydrolysis. Arylesterase activity (AREase) was determined using phenylacetate as a substrate, allowing comparison of PON1 levels across PON1192 genotypes in mothers and children. Phenylacetate hydrolysis is not affected by the Q192R polymorphism. Among newborns, levels of PON1 (AREase) varied by 26-fold (4.3-110.7 U/ml) and among mothers by 14-fold (19.8-281.4 U/ml). On average, children's PON1 levels were four-fold lower than the mothers' PON1 levels (P<0.001). Average PON1 levels in newborns were comparable with reported hPON1 levels in transgenic mice expressing human PON1Q192 or PON1R192, allowing for prediction of relative sensitivity to chlorpyrifos oxon (CPO) and DZO. The predicted range of variability in sensitivity of mothers and children in the same Latino cohort was 65-fold for DZO and 131 to 164-fold for CPO. Overall, these findings indicate that many of the newborns and some of the mothers in this cohort would be more susceptible to the adverse effects of specific organophosphorus pesticide exposure due to their PON1 status. Of particular concern are exposures of pregnant mothers and newborns with low PON1 status.
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toxicity of chlorpyrifos and chlorpyrifos oxon in a transgenic mouse model of the human paraoxonase pon1 q192r polymorphism
Pharmacogenetics and Genomics, 2005Co-Authors: Toby B. Cole, Lucio G. Costa, Rebecca J Richter, Betsy J Walter, Diana M Shih, Aaron D Tward, Aldons J Lusis, Charles Timchalk, Clement E. FurlongAbstract:The Q192R polymorphism of paraoxonase (PON1) has been shown to affect hydrolysis of organophosphorus compounds. The Q192 and R192 alloforms exhibit equivalent catalytic efficiencies of hydrolysis for Diazoxon, the oxon form of the pesticide (DZ). However, the R192 alloform has a higher catalytic efficiency of hydrolysis than does the Q192 alloform for chlorpyrifos oxon (CPO), the oxon form of the pesticide chlorpyrifos (CPS). The current study examined the relevance of these observations for in-vivo exposures to chlorpyrifos and chlorpyrifos oxon. Methods Using a transgenic mouse model we examined the relevance of the Q192R polymorphism for exposure to CPS and CPO in vivo. Transgenic mice were generated that expressed either human PON1Q192 or PON1R192 at equivalent levels, in the absence of endogenous mouse PON1. Dose-response and time course experiments were performed on adult mice exposed dermally to CPS or CPO. Morbidity and acetylcholinesterase (AChE) activity in the brain and diaphragm were determined in the first 24 h following exposure. Results Mice expressing PON1Q192 were significantly more sensitive to CPO, and to a lesser extent CPS, than were mice expressing PON1R192. The time course of inhibition following exposure to 1.2 mg/kg CPO revealed maximum inhibition of brain AChE at 6?12 h, withmore » PON1R192, PON1Q192, and PON1? /? mice exhibiting 40, 70 and 85% inhibition, respectively, relative to control mice. The effect of PON1 removal on the dose?response curve for CPS exposure was remarkably consistent with a PBPK/PD model of CPS exposure. Conclusion These results indicate that individuals expressing only the PON1Q192 allele would be more sensitive to the adverse effects of CPO or CPS exposure, especially if they are expressing a low level of plasma PON1Q192.« less
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vitamin c and e intake is associated with increased paraoxonase activity
Arteriosclerosis Thrombosis and Vascular Biology, 2002Co-Authors: Gail P Jarvik, Rebecca J Richter, Victoria H. Brophy, Thomas S Hatsukami, Gerard D Schellenberg, Nancey Trevanian Tsai, Laura A Mckinstry, Roohi Wani, Patrick J Heagerty, Clement E. FurlongAbstract:Objective— Paraoxonase (PON1), an esterase physically associated with high density lipoprotein, has been shown to inhibit atherogenic low density lipoprotein and high density lipoprotein oxidation. PON1 activity appears to be primarily under genetic control with some environmental modification and is a predictor of vascular disease. Vitamins C and E, dietary antioxidants, scavenge free-oxygen radical products that may depress PON1 activity. Therefore, we evaluated the relationship between dietary vitamin C and E intake and PON1 activity. Methods and Results— The vitamin C and E intakes of male white subjects (n=189) were estimated by using a standardized food frequency survey. With covariates, vitamin C or E intakes were found to be significant positive predictors of PON1 activity for the hydrolysis of paraoxon and Diazoxon with the use of linear regression. Smoking and use of statins were independent predictors of PON1 activity. Conclusions— PON1 activity, which is primarily genotype dependent, varies wi...
Alan J. Hargreaves - One of the best experts on this subject based on the ideXlab platform.
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phenyl saligenin phosphate induced caspase 3 and c jun n terminal kinase activation in cardiomyocyte like cells
Chemical Research in Toxicology, 2015Co-Authors: Shatha G. Felemban, Alan J. Hargreaves, Fathi A. Smida, David J. Boocock, A C Garner, John M. DickensonAbstract:At present, little is known about the effect(s) of organophosphorous compounds (OPs) on cardiomyocytes. In this study, we have investigated the effects of phenyl saligenin phosphate (PSP), two organophosphorothioate insecticides (diazinon and chlorpyrifos), and their acutely toxic metabolites (Diazoxon and chlorpyrifos oxon) on mitotic and differentiated H9c2 cardiomyoblasts. OP-induced cytotoxicity was assessed by monitoring MTT reduction, LDH release, and caspase-3 activity. Cytotoxicity was not observed with diazinon, Diazoxon, or chlorpyrifos oxon (48 h exposure; 200 μM). Chlorpyrifos-induced cytotoxicity was only evident at concentrations >100 μM. In marked contrast, PSP displayed pronounced cytotoxicity toward mitotic and differentiated H9c2 cells. PSP triggered the activation of JNK1/2 but not ERK1/2, p38 MAPK, or PKB, suggesting a role for this pro-apoptotic protein kinase in PSP-induced cell death. The JNK1/2 inhibitor SP 600125 attenuated PSP-induced caspase-3 and JNK1/2 activation, confirming the role of JNK1/2 in PSP-induced cytotoxicity. Fluorescently labeled PSP (dansylated PSP) was used to identify novel PSP binding proteins. Dansylated PSP displayed cytotoxicity toward differentiated H9c2 cells. 2D-gel electrophoresis profiles of cells treated with dansylated PSP (25 μM) were used to identify proteins fluorescently labeled with dansylated PSP. Proteomic analysis identified tropomyosin, heat shock protein β-1, and nucleolar protein 58 as novel protein targets for PSP. In summary, PSP triggers cytotoxicity in differentiated H9c2 cardiomyoblasts via JNK1/2-mediated activation of caspase-3. Further studies are required to investigate whether the identified novel protein targets of PSP play a role in the cytotoxicity of this OP, which is usually associated with the development of OP-induced delayed neuropathy.
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Phenyl Saligenin Phosphate Induced Caspase‑3 and c‑Jun N‑Terminal Kinase Activation in Cardiomyocyte-Like Cells
2015Co-Authors: Shatha G. Felemban, Alan J. Hargreaves, Christopher A. Garner, Fathi A. Smida, David J. Boocock, John M. DickensonAbstract:At present, little is known about the effect(s) of organophosphorous compounds (OPs) on cardiomyocytes. In this study, we have investigated the effects of phenyl saligenin phosphate (PSP), two organophosphorothioate insecticides (diazinon and chlorpyrifos), and their acutely toxic metabolites (Diazoxon and chlorpyrifos oxon) on mitotic and differentiated H9c2 cardiomyoblasts. OP-induced cytotoxicity was assessed by monitoring MTT reduction, LDH release, and caspase-3 activity. Cytotoxicity was not observed with diazinon, Diazoxon, or chlorpyrifos oxon (48 h exposure; 200 μM). Chlorpyrifos-induced cytotoxicity was only evident at concentrations >100 μM. In marked contrast, PSP displayed pronounced cytotoxicity toward mitotic and differentiated H9c2 cells. PSP triggered the activation of JNK1/2 but not ERK1/2, p38 MAPK, or PKB, suggesting a role for this pro-apoptotic protein kinase in PSP-induced cell death. The JNK1/2 inhibitor SP 600125 attenuated PSP-induced caspase-3 and JNK1/2 activation, confirming the role of JNK1/2 in PSP-induced cytotoxicity. Fluorescently labeled PSP (dansylated PSP) was used to identify novel PSP binding proteins. Dansylated PSP displayed cytotoxicity toward differentiated H9c2 cells. 2D-gel electrophoresis profiles of cells treated with dansylated PSP (25 μM) were used to identify proteins fluorescently labeled with dansylated PSP. Proteomic analysis identified tropomyosin, heat shock protein β-1, and nucleolar protein 58 as novel protein targets for PSP. In summary, PSP triggers cytotoxicity in differentiated H9c2 cardiomyoblasts via JNK1/2-mediated activation of caspase-3. Further studies are required to investigate whether the identified novel protein targets of PSP play a role in the cytotoxicity of this OP, which is usually associated with the development of OP-induced delayed neuropathy
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Diazoxon disrupts the expression and distribution of βIII-tubulin and MAP 1B in differentiating N2a cells.
Basic & Clinical Pharmacology & Toxicology, 2014Co-Authors: Magdalini Sachana, John Flaskos, Wayne Harris, Erasmia Sidiropoulou, Alex J. Robinson, Zerai Woldehiwet, Alan J. HargreavesAbstract:This study aimed at assessing the effects of Diazoxon (DZO), a major metabolite of the insecticide diazinon (DZ), on key cytoskeletal proteins in differentiating N2a neuroblastoma cells. Initial experiments established that sub-lethal concentrations of 1, 5 and 10 μM DZO produced profound inhibition of neurite outgrowth. Densitometric scanning of probed immunoblots of N2a cell lysates demonstrated that DZO had no effect on total β-tubulin levels. However, probing with a monoclonal antibody that recognised specifically the βIII-tubulin isotype revealed that 10 μM DZO induced a significant reduction in the levels of this particular form. Levels of polyglutamylated tubulin were not altered. Exposure to 10 μM DZO also decreased the expression of microtubule associated protein 1B (MAP 1B). However, DZO had no effect on the expression of MAP tau. DZO also failed to affect the levels neurofilament light (NFL) and neurofilament medium (NFM) chain levels. Indirect immunofluorescence demonstrated that the staining of neurites in treated cells was weaker than in the controls for βIII-tubulin. In conclusion, DZO disrupts the microtubule (MT) network affecting the expression and distribution of two specific MT proteins known to be important in neuritogenesis. DZO may contribute to the developmental neurotoxicity seen following exposure to DZ.
Lucio G. Costa - One of the best experts on this subject based on the ideXlab platform.
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Paraoxonase (PON1), detoxification of nerve agents, and modulation of their toxicity
Handbook of Toxicology of Chemical Warfare Agents, 2020Co-Authors: Lucio G. Costa, Toby B. Cole, Jacqueline M. Garrick, Judit Marsillach, Clement E. FurlongAbstract:Abstract Paraoxonase (PON1) is a serum and liver enzyme that can hydrolyze in vitro several organophosphorus (OP) compounds, including the active metabolites of specific OP insecticides, and certain OP nerve agents such as sarin and soman. PON1 presents several genetic polymorphisms that influence its ability to hydrolyze OPs as well as its level of expression. Studies in animals, including transgenic mice, have shown that PON1 modulates the in vivo acute toxicity of certain OPs, such as chlorpyrifos oxon and Diazoxon. In contrast, because of its low catalytic efficiency toward paraoxon, PON1 does not influence the acute toxicity of this OP in vivo. The catalytic efficiency of PON1 toward nerve agents is similarly low, though some studies have shown that administration of exogenous PON1 can protect against the toxicity of soman and sarin. For use as catalytic bioscavengers, recombinant engineered PON1s need to be developed with an enhanced catalytic efficiency toward nerve agents being devoid of immunogenicity. Such PON1s would be excellent candidates for prophylactic and therapeutic applications in the case of OP nerve agent poisoning. A parallel strategy would be that of identifying and studying agents which would increase levels of endogenous PON1.
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astrocytes protect against diazinon and Diazoxon induced inhibition of neurite outgrowth by regulating neuronal glutathione
Toxicology, 2014Co-Authors: Daniella Pizzurro, Lucio G. Costa, Khoi DaoAbstract:Abstract Evidence demonstrating that human exposure to various organophosphorus insecticides (OPs) is associated with neurobehavioral deficits in children continues to emerge. The present study focused on diazinon (DZ) and its active oxygen metabolite, Diazoxon (DZO), and explored their ability to impair neurite outgrowth in rat primary hippocampal neurons as a mechanism of developmental neurotoxicity. Both DZ and DZO (0.5–10 μM) significantly inhibited neurite outgrowth in hippocampal neurons, at concentrations devoid of any cyototoxicity. These effects appeared to be mediated by oxidative stress, as they were prevented by antioxidants (melatonin, N-t-butyl-alpha-phenylnitrone, and glutathione ethyl ester). Inhibition of neurite outgrowth was observed at concentrations below those required to inhibit the catalytic activity of acetylcholinesterase. The presence of astrocytes in the culture was able to provide protection against inhibition of neurite outgrowth by DZ and DZO. Astrocytes increased neuronal glutathione (GSH) in neurons, to levels comparable to those of GSH ethyl ester. Astrocytes depleted of GSH by l -buthionine-(S,R)-sulfoximine no longer conferred protection against DZ- and DZO-induced inhibition of neurite outgrowth. The findings indicate that DZ and DZO inhibit neurite outgrowth in hippocampal neurons by mechanisms involving oxidative stress, and that these effects can be modulated by astrocytes and astrocyte-derived GSH. Oxidative stress from other chemical exposures, as well as genetic abnormalities that result in deficiencies in GSH synthesis and regulation, may render individuals more susceptible to these developmental neurotoxic effects of OPs.
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diazinon and Diazoxon impair the ability of astrocytes to foster neurite outgrowth in primary hippocampal neurons
Toxicology and Applied Pharmacology, 2014Co-Authors: Daniella Pizzurro, Lucio G. Costa, Khoi DaoAbstract:Abstract Evidence from in vivo and epidemiological studies suggests that organophosphorus insecticides (OPs) are developmental neurotoxicants, but possible underlying mechanisms are still unclear. Astrocytes are increasingly recognized for their active role in normal neuronal development. This study sought to investigate whether the widely-used OP diazinon (DZ), and its oxygen metabolite Diazoxon (DZO), would affect glial–neuronal interactions as a potential mechanism of developmental neurotoxicity. Specifically, we investigated the effects of DZ and DZO on the ability of astrocytes to foster neurite outgrowth in primary hippocampal neurons. The results show that both DZ and DZO adversely affect astrocyte function, resulting in inhibited neurite outgrowth in hippocampal neurons. This effect appears to be mediated by oxidative stress, as indicated by OP-induced increased reactive oxygen species production in astrocytes and prevention of neurite outgrowth inhibition by antioxidants. The concentrations of OPs were devoid of cytotoxicity, and cause limited acetylcholinesterase inhibition in astrocytes (18 and 25% for DZ and DZO, respectively). Among astrocytic neuritogenic factors, the most important one is the extracellular matrix protein fibronectin. DZ and DZO decreased levels of fibronectin in astrocytes, and this effect was also attenuated by antioxidants. Underscoring the importance of fibronectin in this context, adding exogenous fibronectin to the co-culture system successfully prevented inhibition of neurite outgrowth caused by DZ and DZO. These results indicate that DZ and DZO increase oxidative stress in astrocytes, and this in turn modulates astrocytic fibronectin, leading to impaired neurite outgrowth in hippocampal neurons.
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Paraoxonase 1 (PON1) as a genetic determinant of susceptibility to organophosphate toxicity
Toxicology, 2012Co-Authors: Lucio G. Costa, Gennaro Giordano, Toby B. Cole, Judit Marsillach, Clement E. FurlongAbstract:a b s t r a c t Paraoxonase (PON1) is an A-esterase capable of hydrolyzing the active metabolites (oxons) of a number of organophosphorus (OP) insecticides such as parathion, diazinon and chlorpyrifos. PON1 activity is highest in liver and in plasma. Human PON1 displays two polymorphisms in the coding region (Q192R and L55M) and several polymorphisms in the promoter and the 3 � -UTR regions. The Q192R polymorphism imparts differential catalytic activity toward some OP substrates, while the polymorphism at position −108 (C/T) is the major contributor of differences in the levels of PON1 expression. Both contribute to determining an individual's PON1 "status". Animal studies have shown that PON1 is an important determinant of OP toxicity. Administration of exogenous PON1 to rats or mice protects them from the toxicity of specific OPs. PON1 knockout mice display a high sensitivity to the toxicity of Diazoxon and chlorpyrifos oxon, but not of paraoxon. In vitro catalytic efficiencies of purified PON192 alloforms for hydrolysis of specific oxon substrates accurately predict the degree of in vivo protection afforded by each isoform. Evidence is slowly emerging that a low PON1 status may increase susceptibility to OP toxicity in humans. Low PON1 activity may also contribute to the developmental toxicity and neurotoxicity of OPs, as shown by animal and human studies. © 2012 Published by Elsevier Ireland Ltd.
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toxicity of chlorpyrifos and chlorpyrifos oxon in a transgenic mouse model of the human paraoxonase pon1 q192r polymorphism
Pharmacogenetics and Genomics, 2005Co-Authors: Toby B. Cole, Lucio G. Costa, Rebecca J Richter, Betsy J Walter, Diana M Shih, Aaron D Tward, Aldons J Lusis, Charles Timchalk, Clement E. FurlongAbstract:The Q192R polymorphism of paraoxonase (PON1) has been shown to affect hydrolysis of organophosphorus compounds. The Q192 and R192 alloforms exhibit equivalent catalytic efficiencies of hydrolysis for Diazoxon, the oxon form of the pesticide (DZ). However, the R192 alloform has a higher catalytic efficiency of hydrolysis than does the Q192 alloform for chlorpyrifos oxon (CPO), the oxon form of the pesticide chlorpyrifos (CPS). The current study examined the relevance of these observations for in-vivo exposures to chlorpyrifos and chlorpyrifos oxon. Methods Using a transgenic mouse model we examined the relevance of the Q192R polymorphism for exposure to CPS and CPO in vivo. Transgenic mice were generated that expressed either human PON1Q192 or PON1R192 at equivalent levels, in the absence of endogenous mouse PON1. Dose-response and time course experiments were performed on adult mice exposed dermally to CPS or CPO. Morbidity and acetylcholinesterase (AChE) activity in the brain and diaphragm were determined in the first 24 h following exposure. Results Mice expressing PON1Q192 were significantly more sensitive to CPO, and to a lesser extent CPS, than were mice expressing PON1R192. The time course of inhibition following exposure to 1.2 mg/kg CPO revealed maximum inhibition of brain AChE at 6?12 h, withmore » PON1R192, PON1Q192, and PON1? /? mice exhibiting 40, 70 and 85% inhibition, respectively, relative to control mice. The effect of PON1 removal on the dose?response curve for CPS exposure was remarkably consistent with a PBPK/PD model of CPS exposure. Conclusion These results indicate that individuals expressing only the PON1Q192 allele would be more sensitive to the adverse effects of CPO or CPS exposure, especially if they are expressing a low level of plasma PON1Q192.« less