Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Ross, Matthew K.

Committee Member

Crow, J. Allen

Committee Member

Chambers, Janice E.

Committee Member

Wills, Robert W.

Committee Member

Pruett, Stephen B.

Date of Degree

5-9-2015

Document Type

Dissertation - Open Access

Major

Environmental Toxicology

Degree Name

Doctor of Philosophy

College

College of Veterinary Medicine

Department

Environmental Toxicology Program

Abstract

Evidence suggests that pesticide exposure is a risk factor for atherosclerosis, a pathology involving oxidative stress and dysregulated cholesterol metabolism in monocytes and macrophages as vital causative factors. This research focused on understanding two different mechanisms by which organochlorine and organophosphate pesticides may contribute to atherogenesis. First, the ability of organochlorine insecticides to contribute to elevated oxidative stress was investigated. Urinary concentrations of F2-isoprostanes (a systemic oxidative stress biomarker) and serum levels of the persistent organochlorine compounds p,p’-DDE, trans-nonachlor and oxychlordane were quantified in human samples and the association of these factors with diagnosis of atherosclerosis was described in a cross-sectional study. Subsequently, the ability of three bioaccumulative organochlorine insecticides, trans-nonachlor, dieldrin and p,p’-DDE, to induce the production of superoxide radical anion via NADPH oxidase activation in cultured human THP-1 monocytes through a phospholipase A2 (PLA2)-derived arachidonic acid (AA) signaling cascade was investigated. Trans-nonachlor induced NOX-dependent generation of superoxide/ROS (as measured using three distinct assay types) and stimulated the phosphorylation and membrane translocation of the p47phox regulatory subunit (two biomarkers of Nox activation). Measurement of arachidonic acid and eicosanoid release from OC-exposed monocytes by LC-MS/MS analysis subsequently confirmed the role of PLA2 as a central signaling node in the induction of reactive oxygen production in this process. To investigate a separate mechanism by which organophosphate toxicity may contribute to atherosclerosis, the ability of the esterase/lipase carboxylesterase 1 (CES1), a major enzyme target of OP toxicants, to regulate endocannabinoid and cholesterol homeostasis in human macrophages was assessed. Experimental ablation of CES1 activity altered cholesterol uptake, but not efflux in macrophage foam cells in vitro. Numerous genes involved in the cholesterol homeostatic process, including scavenger receptors (SR-A, CD36), cholesterol transporters (ABCA1, ABCG1), nuclear receptors (LXR, PPAR) and oxysterol forming enzymes (CYP27A1), were profoundly downregulated in CES1 knockdown cells. CES1 appears to play a broad central role in both normal macrophage physiology and the homeostatic response to modified LDL, potentially by liberating esterified molecules from lipoprotein particles that serve as ligands for transcription factors such as PPAR and LXR that control the expression of genes critical to the cholesterol metabolic process.

URI

https://hdl.handle.net/11668/18115

Comments

Monocytes||Macrophages||Reactive Oxygen||Oxidative Stress||Cholesterol||Lipid Metabolism||LDL||Carboxylesterase 1||CES1||Atherosclerosis||Organochlorine||Organophosphate||Insecticide||Environmental Contaminant||Human Exposure||Toxicant

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