CHOLINERGIC INSECTICIDE TOXICOLOGY

Summary

Principal Investigator: JOHN CASIDA
Abstract: Neonicotinoids are the most important new class of insecticides of the last three decades, already accounting for about 10% of the world insecticide market and with major human exposure. They have the same nicotinic acetylcholine receptor (nAChR) target as nicotine but are much more potent and selective for insects. The long term objective is to define the mechanisms of selective toxicity for the major neonicotinoids, imidacloprid, thiacloprid, thiamethoxam and acetamiprid. The first specific aim is to establish the unique neonicotinoid and nicotinoid structural features for nAChR specificity and selective toxicity. The negatively-charged tip is proposed to confer potency and selectivity for insect nAChRs, prompting us to synthesize structural probes with this feature. The preferred conformation and configuration will be determined by X-ray crystallography and NMR and related to potency. Quantum mechanics studies will establish the electrostatic potential surface, molecular charge distribution and binding energy. The same approaches will be used to characterize the analogous nicotinoids selective for mammalian nAChRs. The second aim is to characterize nAChR subtypes, subunits and subsites that determine selective action. One goal is to establish the role(s) of alpha4beta2, alpha3beta2(and/or beta4) alpha5, or alpha7 and alpha1Gamma alpha1deltabeta1 subtypes in binding neonicotinoids and their metabolites relative to functional assays and selective toxicity. Drosophila nAChR and vertebrate nAChR subtypes are solubilized, purified by neonicotinoid- or nicotinoid-affinity chromatography, and labeled with potent azidoneonicotinoid and azidonicotinoid photoaffinity probes designed in this laboratory. The labeled subunits will be identified with particular attention to the proposed cationic subsite(s) in insects and pi-electron-rich subsite(s) in vertebrates. Molecular modeling of the detailed binding site architecture will then relate the structure of the Drosophila D-alpha subunits and the acetylcholine binding protein to the findings on photoaffinity labeling. The third aim is to define neonicotinoid metabolic activation and detoxification relative to selective toxicity. Metabolites of imidacloprid, thiacloprid, thiamethoxam and acetamiprid will be characterized and synthesized for receptor, toxicity and functional assays to clarify selective metabolic activation versus detoxification. Toxicokinetic studies with mice will relate the brain levels of neonicotinoids and their desnitro and descyano metabolites (toxic iminium derivatives) to the poisoning signs. Continuing investigations will define human cytochrome P450 isozyme specificity in metabolism of neonicotinoids and characterize human microsomal "neonicotinoid nitroimine reductase" that generates unique hydrazone and triazolone derivatives of imidacloprid.
Funding Period: 1998-06-01 - 2008-07-31
more information: NIH RePORT

Top Publications

  1. ncbi Molecular features of neonicotinoid pharmacophore variants interacting with the insect nicotinic receptor
    Ikuya Ohno
    Department of Chemistry, Gifu University, Gifu 501 1193, Japan
    Chem Res Toxicol 22:476-82. 2009
  2. ncbi 6'-Methylpyrido[3,4-b]norhomotropane: synthesis and outstanding potency in relation to the alpha4beta2 nicotinic receptor pharmacophore model
    David B Kanne
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720 3112, USA
    Bioorg Med Chem Lett 15:877-81. 2005
  3. ncbi Nitroso-imidacloprid irreversibly inhibits rabbit aldehyde oxidase
    Ryan A Dick
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley 94720 3112, USA
    Chem Res Toxicol 20:1942-6. 2007
  4. pmc Atypical nicotinic agonist bound conformations conferring subtype selectivity
    Motohiro Tomizawa
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720 3112, USA
    Proc Natl Acad Sci U S A 105:1728-32. 2008
  5. pmc Atomic interactions of neonicotinoid agonists with AChBP: molecular recognition of the distinctive electronegative pharmacophore
    Todd T Talley
    Department of Pharmacology, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, La Jolla, CA 99093 0657, USA
    Proc Natl Acad Sci U S A 105:7606-11. 2008
  6. ncbi Potency and selectivity of trifluoroacetylimino and pyrazinoylimino nicotinic insecticides and their fit at a unique binding site niche
    Motohiro Tomizawa
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy, and Management, University of California, Berkeley, California 94720 3112, USA
    J Med Chem 51:4213-8. 2008
  7. ncbi Comparative metabolism and pharmacokinetics of seven neonicotinoid insecticides in spinach
    Kevin A Ford
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720 3112, USA
    J Agric Food Chem 56:10168-75. 2008
  8. ncbi Molecular recognition of neonicotinoid insecticides: the determinants of life or death
    Motohiro Tomizawa
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720 3112, USA
    Acc Chem Res 42:260-9. 2009
  9. ncbi Neonicotinoid substituents forming a water bridge at the nicotinic acetylcholine receptor
    Ikuya Ohno
    Department of Chemistry, Faculty of Education, Gifu University, Gifu, Japan
    J Agric Food Chem 57:2436-40. 2009
  10. pmc Enzymes and inhibitors in neonicotinoid insecticide metabolism
    Xueyan Shi
    Department of Environmental Science, Environmental Chemistry and Toxicology Laboratory, University of California, Berkeley, California 94720 3112, USA
    J Agric Food Chem 57:4861-6. 2009

Scientific Experts

  • Motohiro Tomizawa
  • John E Casida
  • Ryan A Dick
  • Kevin A Ford
  • Ikuya Ohno
  • David B Kanne
  • Hideo Honda
  • Kathleen A Durkin
  • Shinzo Kagabu
  • Xueyan Shi
  • Todd T Talley
  • Yuji Naruse
  • Motohiro Tomizawaa
  • Ryan E Hibbs
  • Zoran Radic
  • Michal Harel
  • Palmer Taylor

Detail Information

Publications24

  1. ncbi Molecular features of neonicotinoid pharmacophore variants interacting with the insect nicotinic receptor
    Ikuya Ohno
    Department of Chemistry, Gifu University, Gifu 501 1193, Japan
    Chem Res Toxicol 22:476-82. 2009
    ..Orientation of the tip oxygen plays a critical role for binding of the NNO and NC(O)H pharmacophores, and the extended NC(O)R and NC(O)OR moieties are embraced by unique binding domains...
  2. ncbi 6'-Methylpyrido[3,4-b]norhomotropane: synthesis and outstanding potency in relation to the alpha4beta2 nicotinic receptor pharmacophore model
    David B Kanne
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720 3112, USA
    Bioorg Med Chem Lett 15:877-81. 2005
    ..In this pharmacophore model, the 6'-methyl substituent may be equivalent to the acetyl methyl of acetylcholine...
  3. ncbi Nitroso-imidacloprid irreversibly inhibits rabbit aldehyde oxidase
    Ryan A Dick
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley 94720 3112, USA
    Chem Res Toxicol 20:1942-6. 2007
    ..These findings demonstrate that IMI-NO is metabolically activated by rabbit AOX to form both an irreversible inhibitor and a reactive intermediate that is capable of covalently binding to protein...
  4. pmc Atypical nicotinic agonist bound conformations conferring subtype selectivity
    Motohiro Tomizawa
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720 3112, USA
    Proc Natl Acad Sci U S A 105:1728-32. 2008
    ..Accordingly, the subtype selectivity is based on two disparate bound conformations of nicotinic agonists, thereby establishing an atypical concept for neonicotinoid versus nicotinoid selectivity between insect and vertebrate nAChRs...
  5. pmc Atomic interactions of neonicotinoid agonists with AChBP: molecular recognition of the distinctive electronegative pharmacophore
    Todd T Talley
    Department of Pharmacology, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, La Jolla, CA 99093 0657, USA
    Proc Natl Acad Sci U S A 105:7606-11. 2008
    ..This template defines the association of interacting amino acids and their energetic contributions to the distinctive interactions of neonicotinoids...
  6. ncbi Potency and selectivity of trifluoroacetylimino and pyrazinoylimino nicotinic insecticides and their fit at a unique binding site niche
    Motohiro Tomizawa
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy, and Management, University of California, Berkeley, California 94720 3112, USA
    J Med Chem 51:4213-8. 2008
    ....
  7. ncbi Comparative metabolism and pharmacokinetics of seven neonicotinoid insecticides in spinach
    Kevin A Ford
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720 3112, USA
    J Agric Food Chem 56:10168-75. 2008
    ..The findings highlight both metabolites common to several neonicotinoids and those that are compound specific...
  8. ncbi Molecular recognition of neonicotinoid insecticides: the determinants of life or death
    Motohiro Tomizawa
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720 3112, USA
    Acc Chem Res 42:260-9. 2009
    ..Therefore, the unique binding conformations of nicotinic agonists in these insect and vertebrate receptor homologues define the basis for molecular recognition of neonicotinoid insecticides as the determinants of life or death...
  9. ncbi Neonicotinoid substituents forming a water bridge at the nicotinic acetylcholine receptor
    Ikuya Ohno
    Department of Chemistry, Faculty of Education, Gifu University, Gifu, Japan
    J Agric Food Chem 57:2436-40. 2009
    ..Therefore, the present SAR study on binding site interactions helps design potent neonicotinoids with novel substituents...
  10. pmc Enzymes and inhibitors in neonicotinoid insecticide metabolism
    Xueyan Shi
    Department of Environmental Science, Environmental Chemistry and Toxicology Laboratory, University of California, Berkeley, California 94720 3112, USA
    J Agric Food Chem 57:4861-6. 2009
    ..Two organophosphorus CYP450 inhibitors partially block IMI, thiacloprid, and CLO metabolism in vivo in mice, elevating brain and liver levels of the parent compounds while reducing amounts of the hydroxylated metabolites...
  11. pmc Nicotinic agonist binding site mapped by methionine- and tyrosine-scanning coupled with azidochloropyridinyl photoaffinity labeling
    Motohiro Tomizawa
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720 3112, USA
    J Med Chem 52:3735-41. 2009
    ..Methionine and tyrosine are the only residues found derivatized, and their reactivity exquisitely depends on the direction of the azido moiety and its apposition to the reactive amino acid side chains...
  12. ncbi Defining nicotinic agonist binding surfaces through photoaffinity labeling
    Motohiro Tomizawa
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720 3112, USA
    Biochemistry 46:8798-806. 2007
    ..These findings enabled us to use AChBP as a structural surrogate to define the nAChR agonist site...
  13. pmc Mapping the elusive neonicotinoid binding site
    Motohiro Tomizawa
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720 3112, USA
    Proc Natl Acad Sci U S A 104:9075-80. 2007
    ..These structural models based on AChBP directly map the elusive neonicotinoid binding site and further describe the molecular determinants of agonists on nicotinic receptors...
  14. ncbi Identification of aldehyde oxidase as the neonicotinoid nitroreductase
    Ryan A Dick
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720 3112, USA
    Chem Res Toxicol 18:317-23. 2005
    ..In contrast, dog, cat, and chicken liver cytosols do not reduce IMI at appreciable rates. AOX, as a neonicotinoid nitroreductase, may limit the persistence of IMI, and possibly other neonicotinoids, in mammals...
  15. ncbi Neonicotinoid insecticide toxicology: mechanisms of selective action
    Motohiro Tomizawa
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720 3112, USA
    Annu Rev Pharmacol Toxicol 45:247-68. 2005
    ..The low affinity of neonicotinoids for vertebrate relative to insect nicotinic receptors is a major factor in their favorable toxicological profile...
  16. ncbi Neo-nicotinoid metabolic activation and inactivation established with coupled nicotinic receptor-CYP3A4 and -aldehyde oxidase systems
    Hideo Honda
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720 3112, USA
    Toxicol Lett 161:108-14. 2006
    ....
  17. ncbi Neonicotinoid nitroguanidine insecticide metabolites: synthesis and nicotinic receptor potency of guanidines, aminoguanidines, and their derivatives
    David B Kanne
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720 3112, USA
    Chem Res Toxicol 18:1479-84. 2005
    ..In sharp contrast, potency at the vertebrate alpha4beta2 nicotinic receptor is generally increased on conversion from the nitroguanidine to aminoguanidine and particularly guanidine derivatives...
  18. ncbi Pharmacological profiles of recombinant and native insect nicotinic acetylcholine receptors
    Motohiro Tomizawa
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, 94720 3112, USA
    Insect Biochem Mol Biol 35:1347-55. 2005
    ..These findings are consistent with the agonist binding site being located at the nAChR subunit interface and indicate that both alpha and beta subunits influence the pharmacological properties of insect nAChRs...
  19. ncbi Substrate specificity of rabbit aldehyde oxidase for nitroguanidine and nitromethylene neonicotinoid insecticides
    Ryan A Dick
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720 3112, USA
    Chem Res Toxicol 19:38-43. 2006
    ..These in vitro observations show large structural differences in the rates of AOX-catalyzed reduction and help to interpret the extensive studies on in vivo metabolism of neonicotinoid insecticides...
  20. ncbi Insect nicotinic acetylcholine receptors: neonicotinoid binding site specificity is usually but not always conserved with varied substituents and species
    Hideo Honda
    Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720 3112, USA
    J Agric Food Chem 54:3365-71. 2006
    ..The TFM moiety of DIN may bind in a different orientation compared to the CPM group of IMI and ACE...
  21. ncbi Chloropyridinyl neonicotinoid insecticides: diverse molecular substituents contribute to facile metabolism in mice
    Kevin A Ford
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, 94720 3112, USA
    Chem Res Toxicol 19:944-51. 2006
  22. ncbi Unique and common metabolites of thiamethoxam, clothianidin, and dinotefuran in mice
    Kevin A Ford
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720 3112, USA
    Chem Res Toxicol 19:1549-56. 2006
    ..The diversity of biodegradable sites and multiple pathways insures against parent compound accumulation but provides intermediates reported to be active as nicotinic agonists and inducible nitric oxide synthase inhibitors...
  23. ncbi Insect muscarinic acetylcholine receptor: pharmacological and toxicological profiles of antagonists and agonists
    Hideo Honda
    Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, California 94720 3112, USA
    J Agric Food Chem 55:2276-81. 2007
    ..The insect mAChR warrants continuing study in lead generation to discover novel insecticides...
  24. ncbi Bis-neonicotinoid insecticides: Observed and predicted binding interactions with the nicotinic receptor
    Ikuya Ohno
    Department of Chemistry, Faculty of Education, Gifu University, Gifu 501 1193, Japan
    Bioorg Med Chem Lett 19:3449-52. 2009
    ....