2007 Progress Report: Genetic Susceptibility to Pesticides

EPA Grant Number: R831709C002
Subproject: this is subproject number 002 , established and managed by the Center Director under grant R831709
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: University of Washington Center for Child Environmental Health Risks Research
Center Director: Faustman, Elaine
Title: Genetic Susceptibility to Pesticides
Investigators: Faustman, Elaine
Institution: University of Washington
EPA Project Officer: Callan, Richard
Project Period: November 1, 2003 through October 31, 2008 (Extended to October 31, 2010)
Project Period Covered by this Report: November 1, 2006 through October 31,2007
RFA: Centers for Children's Environmental Health and Disease Prevention Research (2003) RFA Text |  Recipients Lists
Research Category: Children's Health , Health Effects , Health


The objective of this research project is to identify susceptibility factors for developmental neurotoxicity of pesticides, including genetic polymorphisms.

Progress Summary:

During the past year we have initiated a series of studies aimed at investigating the role of paraoxonase  (PON1) in modulating the toxicity resulting from exposure to mixtures of organophosphorus (OP) compounds. This was prompted by consideration that exposure to OPs commonly involves exposure to more than one compound. There is information available on the potential interactive effects of certain OPs, however, whether and how the known PON1 polymorphisms may affect such interactions is not known. We have carried out a series of studies with chlorpyrifos oxon (CPO), diazoxon (DZO), paraoxon (PO) and malaoxon (MO), the active metabolites of chlorpyrifos, diazionon, parathion and malathion. All are widely used OP insecticides, though parathion is no longer used in the USA.
CPO is metabolized by PON1 in vivo, particularly by the R192 allozyme, while DZO is equally metabolized in vivo by both PON1 192 allozymes. On the other hand, PO does not appear to be metabolized by PON1 in vivo. MO is not a substrate for PON1, but is metabolized by carboxylesterases (CarE). We first found that CPO, DZO and PO are potent inhibitors of CarE, both in vitro and in vivo. When wild-type mice are exposed to CPO (0.75 mg/kg), DZO (0.5 mg/kg), or PO (0.5 mg/kg) and then to different doses (25-100 mg/kg) of MO, the toxicity of the latter [assessed by measuring inhibition of brain acetylcholinesterase (AChE) activity] is increased, compared to mice receiving only MO. Such potentiation is most likely due to inhibition of CarE by CPO, DZO, and PO. The doses of CPO, DZO, and PO caused significant inhibition of plasma CarE but minimal inhibition of liver CarE and only moderate inhibition of brain AChE.  A greater potentiation of MO toxicity is seen with CPO and DZO in PON1 knockout mice, which have much decreased ability to detoxify these two OPs. In contrast, and as predicted, this was not the case with PO.
When comparing hPON1Q192 and hPON1R192 TG mice in the same experimental paradigm, we found that potentiation of MO toxicity was more pronounced in hPON1Q192 mice in case of CPO, because of their lower ability to detoxify CPO. In contrast, potentiation of MO toxicity by DZO was similar in the two TG mice, as both are equally effective at hydrolyzing DZO. In the case of PO, presence or absence of either hPON1192 allele did not alter the degree of potentiation of MO toxicity. These results provide evidence that PON1 status can greatly influence the outcome of combined exposures to certain OPs.
SIGNIFICANCE: There is evidence from studies in various populations that children are exposed, either in utero or postnatally, to different OPs, including those tested in the experiments described above. For example, a recent study in a New York population identified several diethylphosphates (possible metabolites of diazinon or chlorpyrifos, as well as of other OPs) and malathion dicarboxylic acid (a specific metabolite of malathion) in maternal urine (Engel et al. Am. J. Epidemiol. 165: 1397-1404, 2007). The study reported behavioral alterations in newborns, which were associated with the presence of dialkylphosphates and appeared to be modulated by PON1 status. Interactive effects with malathion were not analyzed in this study, but they may be predicted on the basis of our results. It should also be noted that, as with PON1, CarE activity is very low at birth and increases over time.

Future Activities:

In the next year, we will follow up on the observations above, focusing on the relevance of PON1 status for protecting against combined toxicities of OP compounds during postnatal development.  Plasma levels of both carboxylesterase and PON1 increase over the postnatal period between PN4 and PN21.  At PN4, PN7, PN14, and PN21, mice of different PON1 genotypes (wildtype, PON1-KO, hPON1Q192, and hPON1R192) will be exposed acutely to either CPO or DZO, followed by assessment of carboxylesterase inhibition.  In the next experiments, mice will be exposed sequentially to either CPO or DZO, followed by malaoxon, to assess the relevance of the carboxylesterase inhibition for potentiation of malaoxon toxicity at PN4, PN7, PN14, and PN21.
We also plan to do a series of experiments to assess the effects of chronic CPO exposure during postnatal development, using histopathology and gene expression as endpoints.  In our previous experiments, histopathological effects in the cerebral cortex were subtle and difficult to quantify, and variability among individuals resulted in inconclusive results with neocortical gene expression as the endpoint.  We plan to address these issues by doing a new set of experiments that focuses on the cerebellum and spinal cord as potential targets of toxicity.  Wild-type, PON1-KO, hPON1R192 and hPON1Q192 mice will be exposed to 0.25 mg/kg/d CPO from PN4 to PN21, and histopathology will be assessed in perfusion-fixed brains and spinal cords of mice at PN22 and PN80, through a collaboration with Hiroshi Mitsumoto and Chris Henderson at Columbia University Medical Center.  Drs. Mitsumoto and Henderson have also been sent brain sections from our previous experiment, for independent, blind assessment of histopathology in these samples. Littermates of the mice used for histopathology will be used to assess gene expression in the cerebellum.  The cerebellum is used because it has been shown as a target of chlorpyrifos toxicity and because its well-defined borders greatly reduce inter-individual variability due to differences in dissection.  Gene expression will be assessed using Affymetrix mouse arrays hybridized with labeled RNA from individual animals, instead of pooled samples, with five biological replicates.  This approach should limit sources of variability among samples and provide enough replicates to obtain meaningful data on the chronic toxicity of CPO.  Microarray data will be anchored to the CPO-related changes in baseline brain cholinesterase we observed in our previous experiments.

Journal Articles on this Report : 3 Displayed | Download in RIS Format

Other subproject views: All 32 publications 29 publications in selected types All 19 journal articles
Other center views: All 175 publications 127 publications in selected types All 107 journal articles
Type Citation Sub Project Document Sources
Journal Article Costa LG, Cole TB, Furlong CE. Gene-environment interactions:paraoxonase (PON1) and sensitivity to organophosphate toxicity. LabMedicine 2006;37(2):109-113. R831709 (2005)
R831709 (2007)
R831709C001 (2007)
R831709C002 (2007)
  • Full-text: Oxford-Full Text PDF
  • Abstract: Oxford-Abstract
  • Journal Article Costa LG, Giordano G, Guizzetti M, Vitalone A. Neurotoxicity of pesticides: a brief review. Frontiers in Bioscience 2008;13(4):1240-1249. R831709 (2005)
    R831709 (2007)
    R831709C001 (2007)
    R831709C002 (2007)
  • Abstract from PubMed
  • Full-text: Bioscience - Full Text HTML
  • Abstract: ResearchGate - Abstract
  • Journal Article Giordano G, Afsharinejad Z, Guizzetti M, Vitalone A, Kavanagh TJ, Costa LG. Organophosphorus insecticides chlorpyrifos and diazinon and oxidative stress in neuronal cells in a genetic model of glutathione deficiency. Toxicology and Applied Pharmacology 2007;219(2-3):181-189. R831709 (2005)
    R831709 (2006)
    R831709 (2007)
    R831709C001 (2006)
    R831709C001 (2007)
    R831709C002 (2007)
  • Abstract from PubMed
  • Full-text: ScienceDirect - Full Text HTML
  • Abstract: ScienceDirect - Abstract
  • Other: ScienceDirect - Full Text PDF
  • Supplemental Keywords:

    children’s health, epidemiology, genetics, health risk assessment, risk assessment, assessment of exposure, asthma, children’s environmental health, diesel exhaust, environmental risks, exposure assessment, genetic mechanisms, genetic risk factors, genetic susceptibility, maternal exposure, nutritional risk factors, Environmental Management, Scientific Discipline, Health, RFA, Risk Assessment, Health Risk Assessment, Children's Health, Biochemistry, Environmental Chemistry, health effects, children's environmental health, assessment of exposure, developmental neurotoxicity, agricultural community, community-based intervention, pesticide exposure, genetic polymorphisms, biological response, environmental health, environmental risks, children's vulnerability
    , RFA, Health, Scientific Discipline, ENVIRONMENTAL MANAGEMENT, Health Risk Assessment, Biochemistry, Children's Health, Risk Assessment, environmental health, health effects, pesticide exposure, community-based intervention, developmental neurotoxicity, biological response, environmental risks, Human Health Risk Assessment, assessment of exposure, children's vulnerablity, genetic polymorphisms

    Progress and Final Reports:

    Original Abstract
  • 2004 Progress Report
  • 2005 Progress Report
  • 2006 Progress Report
  • 2008
  • 2009
  • Final

  • Main Center Abstract and Reports:

    R831709    University of Washington Center for Child Environmental Health Risks Research

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R831709C001 Molecular Mechanisms of Pesticide-Induced Developmental Toxicity
    R831709C002 Genetic Susceptibility to Pesticides
    R831709C003 Community-Based Participatory Research Project
    R831709C004 Pesticide Exposure Pathways Research Project