ToxSci Advance Access originally published online on October 5, 2006
Toxicological Sciences 2007 95(1):136-146; doi:10.1093/toxsci/kfl127
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Structure-Toxicity Analysis of Type-2 Alkenes: In Vitro Neurotoxicity
* Department of Anesthesiology, Albert Einstein College of Medicine, Montefiore Medical Center, Bronx, New York 10467
Center for Environmental and Human Toxicology, University of Florida, Gainesville, Florida 32611-0885
Department of Chemistry, Iona College, New Rochelle, New York 10804
1To whom correspondence should be addressed at Montefiore Medical Center, Moses Research Tower-7, 111 East 210th Street, Bronx, NY 10467. Fax: (718) 515-4903. E-mail: lopachin{at}aecom.yu.edu.
Received July 12, 2006; accepted September 23, 2006
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Abstract |
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Acrylamide (ACR) is a conjugated type-2 alkene that produces synaptic toxicity presumably by sulfhydryl adduction. The 
,ß-unsaturated carbonyl of ACR is a soft electrophile and, therefore, adduction of nucleophilic thiol groups could occur through a conjugate (Michael) addition reaction. To address the mechanism of thiol adduct formation and corresponding neurotoxicological importance, we defined structure-toxicity relationships among a series of conjugated type-2 alkenes (1µM–10mM), which included acrolein and methylvinyl ketone. Results show that exposure of rat striatal synaptosomes to these chemicals produced parallel, concentration-dependent neurotoxic effects that were correlated to loss of free sulfhydryl groups. Although differences in relative potency were evident, all conjugated analogs tested were equiefficacious with respect to maximal neurotoxicity achieved. In contrast, nonconjugated alkene or aldehyde congeners did not cause synaptosomal dysfunction or sulfhydryl loss. Acrolein and other ,ß-unsaturated carbonyls are bifunctional (electrophilic reactivity at the C-1 and C-3 positions) and could produce in vitro neurotoxicity by forming protein cross-links rather than thiol monoadducts. Immunoblot analysis detected slower migrating, presumably derivatized, synaptosomal proteins only at very high acrolein concentrations (
25mM). Exposure of synaptosomes to high concentrations of ACR (1M), N-ethylmaleimide (10mM), and methyl vinyl ketone (MVK) (100mM) did not alter the gel migration of synaptosomal proteins. Furthermore, hydralazine (1mM), which blocks the formation of protein cross-links, did not affect in vitro acrolein neurotoxicity. Thus, type-2–conjugated alkenes produced synaptosomal toxicity that was linked to a loss of thiol content. This is consistent with our hypothesis that the mechanism of ACR neurotoxicity involves formation of Michael adducts with protein sulfhydryl groups.
Key Words: distal axonopathy; acrolein; acrylamide; adduct formation; neurodegeneration; synapse.
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