title: Biological assessment of neonicotinoids imidacloprid and its major metabolites for potentially human health using globular proteins as a model.
abstract: The assessment of biological activities of imidacloprid and its two major metabolites, namely 6-chloronicotinic acid and 2-imidazolidone for nontarget organism, by employing essentially functional biomacromolecules, albumin and hemoglobin as a potentially model with the use of circular dichroism (CD), fluorescence, extrinsic 8-anilino-1-naphthalenesulfonic acid (ANS) fluorescence as well as molecular modeling is the theme of this work. By dint of CD spectra and synchronous fluorescence, it was clear that the orderly weak interactions between amino acid residues within globular proteins were disturbed by imidacloprid, and this event led to marginally alterations or self-regulations of protein conformation so as to lodge imidacloprid more tightly. Both steady state and time-resolved fluorescence suggested that the fluorescence of Trp residues in proteins was quenched after the presence of imidacloprid, corresponding to noncovalent protein-imidacloprid complexes formation and, the reaction belongs to moderate association (K=1.888/1.614×10(4)M(-1) for albumin/hemoglobin-imidacloprid, respectively), hydrogen bonds and π stacking performed a vital role in stabilizing the complexes, as derived from thermodynamic analysis and molecular modeling. With the aid of hydrophobic ANS experiments, subdomain IIA and α1β2 interface of albumin and hemoglobin, respectively, were found to be preserved high-affinity for imidacloprid. These results ties in with the subsequently molecular modeling laying imidacloprid in the Sudlow's site I and close to Trp-213 residue on albumin, while settling down B/Trp-37 residue nearby in hemoglobin, and these conclusions further confirmed by site-directed mutagenesis and molecular dynamics simulation. But, at the same time, several crucial noncovalent bonds came from other amino acid residues, e.g. Arg-194 and Arg-198 (albumin) and B/Arg-40, B/Asp-99 and B/Asn-102 (hemoglobin) cannot be ignored completely. Based on the comparative studies of binding modes between imidacloprid and its two primary metabolites with globular proteins, it is evident to us that the noncovalent interactions of 6-chloronicotinic acid and 2-imidazolidone with biopolymers are not always to be decreased obviously as a result of the relatively small molecular structures of these metabolites, compared with parent compound imidacloprid. Conversely, this could probably strengthen the weak interactions existed in the macromolecules-metabolites conjugation, or rather, the metabolites such as 6-chloronicotinic acid and 2-imidazolidone contributed drastically to the overall toxicity of imidacloprid.
authors.affiliation: College of Agriculture and Plant Protection, Qingdao Agricultural University, Qingdao 266109, China; Department of Chemistry, China Agricultural University, Beijing 100193, China; Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, United States.
authors.forename: Fei
authors.initials: F
authors.lastname: Ding
authors.affiliation: College of Agriculture and Plant Protection, Qingdao Agricultural University, Qingdao 266109, China; College of Food Science and Engineering, Qingdao Agricultural University, Qingdao 266109, China. Electronic address: wpeng@qau.edu.cn.
authors.forename: Wei
authors.initials: W
authors.lastname: Peng
mesh_terms: D000817:Anilino Naphthalenesulfonates / Q000737:chemistry; D001665:Binding Sites; D002942:Circular Dichroism; D006454:Hemoglobins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007093:Imidazoles / Q000009:adverse effects* / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D048289:Imidazolidines / Q000737:chemistry / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D000073943:Neonicotinoids; D009539:Nicotinic Acids / Q000737:chemistry / Q000378:metabolism; D009574:Nitro Compounds / Q000009:adverse effects* / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D011487:Protein Conformation; D012710:Serum Albumin, Bovine / Q000737:chemistry / Q000378:metabolism; D013050:Spectrometry, Fluorescence
chemical_list: C000604522:2-imidazolidone; C515594:8-anilino-1-naphthalenesulfonic acid; D000817:Anilino Naphthalenesulfonates; D006454:Hemoglobins; D007093:Imidazoles; D048289:Imidazolidines; D000073943:Neonicotinoids; D009539:Nicotinic Acids; D009574:Nitro Compounds; D012710:Serum Albumin, Bovine; C082359:imidacloprid; C035953:6-chloronicotinic acid