Year of Award

2007

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Pharmaceutical Sciences

Other Degree Name/Area of Focus

Pharmacology

Department or School/College

College of Health Professions and Biomedical Sciences

Committee Chair

Howard D. Beall

Commitee Members

J. Douglas Coffin, Jean C. Pfau, Fernando Cardozo-Pelaez, Scott Wetzel, Stephen Lodmell

Keywords

Health Sciences, Pharmacology

Abstract

Epidemiological studies as well as controlled animal studies have associated exposure to arsenic through drinking water with the development of atherosclerosis. In this study, we have shown for the first time that low and environmentally relevant concentrations of arsenic accelerate atherogenesis. The objective of this study was to elucidate the mechanisms of arsenic-induced atherosclerosis by (1) characterizing the time- and concentration-dependent effects of sodium arsenite [As(III)] on the development of atherosclerosis in ApoE-/- /LDLr-/- mice, (2) determining whether As(III)-induced peroxynitrite activates protein kinase C (PKC) isotypes, α and β, in human aortic endothelial cells (HAECs) and (3) determining the effects of activation of PKC isotypes, α and β, on the endothelial barrier. Accordingly, exposure of ApoE-/- /LDLr-/- mice to As(III) in drinking water showed an increasing trend in atherosclerotic plaque formation in as early as 5 weeks within the innominate arteries. Most remarkable was the evidence that environmentally relevant concentrations of As(III) resulted in significant increase in plaque formation. Initiation of atherosclerosis results from activation/dysfunction of the vascular endothelium that maintains a semipermeable barrier between the blood and vessel wall. To elucidate the mechanism of arsenic-induced atherosclerosis, we analyzed the effect of As(III) on the endothelial monolayer integrity. Endothelial barrier is maintained by proteins of the adherens junction (AJ) such as vascular endothelial cadherin (VE-cadherin) and β-catenin, and their association with the actin cytoskeleton. Treatment of HAECs with As(III) resulted in reorganization of actin filaments into stress fibers and non-uniform VE-cadherin and β-catenin staining at cell-cell junctions. Intercellular gaps were observed with a measured increase in endothelial permeability. In addition, an increase in tyrosine phosphorylation (PY) of β-catenin was observed. These effects were mediated through As(III)-induced activation of PKCα without peroxynitrite formation. No change in PKCβ levels was detected with As(III) treatment. Inhibition of PKCα restored VE-cadherin and β-catenin staining at cell-cell junctions and abolished the formation of intercellular gaps and stress fibers. Endothelial permeability and PY of β-catenin were also reduced to basal levels. These results demonstrate that As(III) induced activation of PKCα causes PY of β-catenin and formation of stress fibers. PY of β-catenin causes weakening of the AJ and this in association with the contractile force generated by stress fibers results in gap formation and increased endothelial permeability. This could potentially accelerate the development of atherosclerosis by increasing the accumulation of oxidized low density lipoproteins and monocytes into the neo-intima of the blood vessel. The findings in this study demonstrate that arsenic disrupts the endothelial monolayer by activation of PKC signaling. Damage to the endothelium plausibly accelerates the process of atherosclerosis at an early stage as evidenced by the increase in atherosclerotic plaques in the ApoE-/- /LDLr-/- mouse model.

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© Copyright 2007 Flavia Elias Pereira