The Nerve Terminal as the Site of Action for Type-2 Alkenes

Albert Einstein College Of Medicine, Bronx NY

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Abstract

DESCRIPTION (provided by applicant): Our research (yrs 1-24) has shown that subchronic systemic acrylamide (ACR) exposure causes cumulative neurotoxicity mediated by selective damage of central and peripheral nerve terminals. ACR is an alpha, beta-unsaturated carbonyl derivative of the type-2 alkene chemical class, which includes other structurally related electrophilic chemicals; e.g., acrolein, 4-hydroxy-2-nonenal (HNE) and methyl acrylate (MA). The type- 2 alkenes are prevalent dietary contaminants and environmental pollutants that have significant toxicological consequences. In addition, unsaturated aldehydes such as acrolein and HNE are produced during membrane lipid peroxidation associated with cellular oxidative stress. These endogenous type-2 alkenes appear to play a pathogenic role in many disease processes and traumatic tissue injuries that have oxidative stress as a common molecular etiology; e.g., spinal cord trauma, atherosclerosis and Alzheimer's disease (AD). During the current funding period (yrs 21-24), we demonstrated that the type-2 alkenes cause toxicity through a common mechanism of action; i.e., protein inactivation via formation of Michael-type adducts with nucleophilic sulfhydryl thiolate groups on active site cysteine residues. Therefore, we propose that environmentally-derived type-2 alkene toxicants act either synergistically or additively with endogenously generated unsaturated aldehydes. This interaction could accelerate the onset of the disease/injury process and amplify the extent of cellular damage. Two specific aims have been designed to investigate the putative interactions of systemically administered toxicants with endogenous neurodegenerative processes in a transgenic mouse model of Alzheimer's disease (AD). Despite the neurocentric focus of these aims, the data and derived concepts are applicable to the type-2 alkene interactions that possibly accelerate certain systemic diseases. Specific Aim 1 research will test the hypothesis that weak electrophiles of the type-2 alkene chemical class (e.g., ACR, MA) cause cumulative neurotoxicity mediated by nerve terminal dysfunction. This proposal is novel and is consistent with the differential CNS accessibility of weak, but not strong, electrophiles and the unique vulnerability of nerve terminals to electrophili attack. The results have significant implications for how we consider electrophilic environmental toxicants and evaluate their neurotoxic risk potential. Specific Aim 2 studies will investigate the possibility that weak electrophiles such as ACR and MA administered systemically can interact with endogenously generated type-2 alkenes to accelerate ongoing neurodegenerative processes in the Tg2576 mouse model of AD. This toxicologically plausible proposal could provide a conceptual framework for molecular-level investigations of other disease processes that have suspected environmental components, such as Parkinson's disease (PD) and atherosclerosis. Our research during the current funding period also showed that 2-acetylcyclopentanone and other nucleophilic 1,3-dicarbonyl enols could prevent oxidative stress-induced toxicity in vitro. Consequently, Specific Aim 3 studies will determine the relative abilities of these enols to modify the onset and development of neurodegenerative processes in Tg2576 mice. Pharmacotherapeutic approaches based on 1,3-dicarbonyl enol chemistry might improve management of numerous human disease processes that involve cellular oxidative stress. This cytoprotection could include inhibition of both the endogenous disease process and the exacerbating actions of exogenous type-2 alkenes. Furthermore, most toxic environmental chemicals or their active metabolites are electrophiles (e.g., acrolein, ACR, methyl mercury) that produce cytotoxicity by reacting with nucleophilic targets on macromolecules. The 1,3-dicarbonyl compounds, through their actions as surrogate nucleophiles, could prevent or minimize damage associated with environmentally acquired type-2 alkene toxicity.