title: Glufosinate binds N-methyl-D-aspartate receptors and increases neuronal network activity in vitro.
abstract: Glufosinate (GLF) at high levels in mammals causes convulsions and amnesia through a mechanism that is not completely understood. The structural similarity of GLF to glutamate (GLU) implicates the glutamatergic system as a target for GLF neurotoxicity. The current work examined in vitro GLF interaction with N-methyl-D-aspartate subtype GLU receptors (NMDARs) and GLT-1 transporters via [(3)H]CGP 39653 binding experiments and [(3)H]GLU uptake assays, respectively. GLF effects on neuronal network activity were assessed using microelectrode array (MEA) recordings in primary cultures of cortical neurons. GLF and its primary metabolite N-acetylglufosinate (NAcGLF) bind to the NMDAR; the IC50 value for GLF was 668 μM and for NAcGLF was about 100 μM. Concentrations of GLF greater than 1000 μM were needed to decrease GLU uptake through GLT-1. In MEA recordings from networks of rat primary cortical neurons, the concentration-responses for NMDA, GLF and NAcGLF on network mean firing rates (MFR) were biphasic, increasing at lower concentrations and decreasing below control levels at higher concentrations. Increases in MFR occurred between 3-10 μM NMDA (290% control, maximum), 100-300 μM NAcGLF (190% control, maximum) and 10-1000 μM GLF (340% control, maximum). The NMDAR antagonist MK801 attenuated both NMDA and GLF increases in MFR. The GLF concentration required to alter GLU transport through GLT-1 is not likely to be attained in vivo, and therefore not relevant to the neurotoxic mode of action. However, toxicokinetic data from reports of intentional human poisonings indicate that GLF concentrations in the CNS after acute exposure could reach levels high enough to lead to effects mediated via NMDARs. Furthermore, the newly characterized action of NAcGLF at the NMDAR suggests that both the parent compound and metabolite could contribute to neurotoxicity via this pathway.
authors.affiliation: Environmental Chemistry and Toxicology Laboratory, Department of Nutritional Sciences and Toxicology, University of California, Berkeley, CA 94720, United States. Electronic address: stephen_lantz@fws.gov.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Lantz
authors.affiliation: Integrated Systems Toxicology Division, MD-B105-03, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, United States.
authors.forename: Cina M
authors.initials: CM
authors.lastname: Mack
authors.affiliation: Integrated Systems Toxicology Division, MD-B105-03, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, United States.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Wallace
authors.affiliation: Environmental Chemistry and Toxicology Laboratory, Department of Nutritional Sciences and Toxicology, University of California, Berkeley, CA 94720, United States.
authors.forename: Ellen F
authors.initials: EF
authors.lastname: Key
authors.affiliation: Integrated Systems Toxicology Division, MD-B105-03, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, United States.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Shafer
authors.affiliation: Environmental Chemistry and Toxicology Laboratory, Department of Nutritional Sciences and Toxicology, University of California, Berkeley, CA 94720, United States.
authors.forename: John E
authors.initials: JE
authors.lastname: Casida
mesh_terms: D000613:Aminobutyrates / Q000378:metabolism / Q000493:pharmacokinetics*; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D051272:Glucose Transporter Type 1 / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008839:Microelectrodes; D009415:Nerve Net / Q000187:drug effects* / Q000378:metabolism; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*
chemical_list: D000613:Aminobutyrates; D051272:Glucose Transporter Type 1; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; C003121:phosphinothricin
keywords: Glufosinate; N-Acetylglufosinate; N-Methyl-d-aspartate receptor; Neurotoxicity