Superfund Research Program
Mechanism of Arsenic-Induced Vascular Disease
Project Leader: Aaron Barchowsky (University of Pittsburgh)
Grant Number: P42ES007373
Funding Period: 2000-2005
Drinking water in many countries, including the United States, can contain levels of arsenic that are associated with increased incidence of occlusive vascular diseases and hypertension. While these diseases are associated with inappropriate growth of blood vessel walls and constriction of blood flow, the mechanisms through which arsenic, especially in its more toxic trivalent forms (e.g., arsenite and its metabolites), promotes this aberrant growth are relatively unknown. The current working hypothesis in Project 1 is that reactive oxygen production in the membranes of the endothelial and smooth muscle cells in vessels exposed to arsenite enhances smooth muscle cell growth.
The first goal was to demonstrate that the effects of arsenite on the transcription factor NF-kB were dose-dependent. The data published in Roussel et al. (2000) were the first to show that high doses of arsenite directly inactivate enzymes involved in NF-kB activation. This contrasts with the earlier observation that low, environmentally relevant levels of arsenite stimulate NF-kB-dependent transactivation (Barchowsky et al. 1996, 1999).
The second goal was to identify the source of reactive oxygen that is stimulated by arsenite in endothelial cells. The data published in Smith et al. (2001) demonstrate that the NADPH oxidase enzyme complex on the surface of the endothelial cells is the primary mediator of arsenite-stimulated cell signaling. Two interesting points regarding this study are that arsenite differs from cytokines in the mechanisms for enzyme activation and that high levels of arsenite actually inhibit this enzyme complex. The fact that these higher levels inhibit NADPH oxidase suggests that this enzyme is the source of oxidants for the effects of low-level arsenite exposure on cell proliferation, but not the source of oxidants that cause arsenite-induced cell death.
Future cell culture-based studies in Project 1 will identify the cellular switch that arsenite uses to activate NADPH oxidase and how this switch affects the proliferative endothelial and smooth muscle cell phenotypes. Additional studies will extend these culture-based observations to in vivo mouse models with a focus on the mechanism for the negative effects of arsenite on the fibrinolytic system. This system is involved in removing the blood clots and preventing the vascular remodeling associated with occlusive disease. These studies will be an extension of past studies of chromium-induced (Shumilla et al. 1999) and more recently nickel-induced (Andrew et al. 2000, 2001a, 2001b) inhibition of airway cell fibrinolysis. These nickel studies were partially supported by the Training Core and helped Angeline Andrew to earn the prestigious Wetterhahn Award from the SBRP in 2000. Finally, future studies in Project 1 will improve the understanding of how low arsenite exposure causes vascular disease and will also provide fundamental insight into mechanisms for arsenite-induced signaling that could lead to other proliferative diseases, such as cancer.