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ToxSci Advance Access originally published online on May 5, 2009
Toxicological Sciences 2009 110(1):168-180; doi:10.1093/toxsci/kfp091
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© The Author 2009. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org
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Neurotoxicogenomic Investigations to Assess Mechanisms of Action of the Munitions Constituents RDX and 2,6-DNT in Northern Bobwhite (Colinus virginianus)

Kurt A. Gust*,1, Mehdi Pirooznia{dagger}, Michael J. Quinn, Jr{ddagger}, Mark S. Johnson{ddagger}, Lynn Escalon§, Karl J. Indest*, Xin Guan§, Joan Clarke*, Youping Deng§, Ping Gong§ and Edward J. Perkins*

* U.S. Army Corps of Engineers, Environmental Laboratory, EP-P, Vicksburg, MS 39180 {dagger} The Johns Hopkins University, School of Medicine, Baltimore, MD 21287 {ddagger} U.S. Army Center for Health Promotion and Preventative Medicine, Edgewood, MD 21010 § SpecPro Inc., ERDC-USACE-EL-EP-P, Vicksburg, MS 39180

1 To whom correspondence should be addressed. Fax: 601-634-4002. E-mail: kurt.a.gust{at}usace.army.mil.

Received February 9, 2009; accepted April 20, 2009


  Abstract

Munitions constituents (MCs) including hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 2,4,6-trinitrotoluene (TNT), and TNT derivatives are recognized to elicit aberrant neuromuscular responses in many species. The onset of seizures resulting in death was observed in the avian model Northern bobwhite after oral dosing with RDX beginning at 8 mg/kg/day in subacute (14 days) exposures, whereas affective doses of the TNT derivative, 2,6-dinitrotoluene (2,6-DNT), caused gastrointestinal impacts, lethargy, and emaciation in subacute and subchronic (60 days) exposures. To assess and contrast the potential neurotoxicogenomic effects of these MCs, a Northern bobwhite microarray was developed consisting of 4119 complementary DNA (cDNA) features enriched for differentially-expressed brain transcripts from exposures to RDX and 2,6-DNT. RDX affected hundreds of genes in brain tissue, whereas 2,6-DNT affected few (≤ 17), indicating that 2,6-DNT exposure had relatively little impact on the brain in comparison to RDX. Birds exhibiting RDX-induced seizures accumulated over 20x more RDX in brain tissues in comparison to non-seizing birds even within a common dose. In parallel, expression patterns were unrelated among seizing and non-seizing birds exposed to equivalent RDX doses. In birds experiencing seizures, genes related to neuronal electrophysiology and signal transduction were significantly affected. Comparative toxicology revealed strong similarity in acute exposure effects between RDX and the organochlorine insecticide dichlorodiphenyltrichloroethane (DDT) regarding both molecular mechanisms and putative mode of action. In a manner similar to DDT, we hypothesize that RDX elicits seizures by inhibition of neuronal cell repolarization postaction potential leading to heightened neuronal excitability and seizures facilitated by multiple molecular mechanisms.

Key Words: munitions constituents; genomics; mechanisms of action; seizures.


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