Long Term Cardiovascular Effects of Inhaled Nanoparticles
Lung-Chi Chen, Ph.D.
The objective of this study is to determine the long-term cardiovascular effects of inhaled nanoparticles. The hypothesize that long-term inhalation of nanoparticles can enhance the development and progression of vascular dysfunction leading to atherosclerosis in a sensitive animal model, and that the vascular dysfunction process is mediated by oxidative stress through the disruption of nitric oxide (NO) regulation. Preliminary studies have demonstrated that 6 months of 6-hr weekday exposures of mice lacking apolipoprotein E (ApoE-/-) to fine ambient concentrated particles enhanced atherosclerosis, and altered vasoconstrictor responses to phenylephrine and serotonin challenge in the thoracic aorta. These changes were accompanied by marked increases in macrophage infiltration, the inducible isoform of nitric oxide synthase (iNOS), increased generation of reactive oxygen species (ROS) and greater immunostaining for the protein nitration product 3-nitrotyrosine. Since nanoparticles have been shown to be able to penetrate into the systemic circulation after inhalation, and are capable of affecting endothelial cell function, it is likely that manufactured nanoparticles could produce cardiovascular effects similar to those seen in preliminary studies. While a tremendous amount of research has addressed the greater pulmonary toxicity associated with ultrafine particles (< 100nm) compared to fine or coarse sized particles, little research has examined the cardiovascular effects of ultrafine or nanoparticles (< 50nm). Furthermore, the few studies that have investigated the cardiovascular effects of inhaled particles were short-term exposure in.nature. To date, there is no study that has investigated the chronic cardiovascular effects of inhaled nanoparticles. Three different nanoparticles will be used to test the hypothesis, nickel, titanium, and carbon. Nanoparticles (count median diameter = 20 nm) will be produced using a spark generator with pure electrodes of nickel, titanium, and carbon. ApoE (-/-) mice will be exposed to 0 (filtered air control), 25, 50, or 100 ng/m3 nanoparticles for 6 hr/d, 5 d/wk, for up to 6 months. The development and progression of atherosclerosis will be assessed using non-invasive ultrasound biomicroscopy (UBM) as well as serial morphometric measurements. Serial endpoints such as vasoconstriction response, macrophage infiltration, NOS expression level (both inducible and endothelial isoforms), ROS, and 3-nitrotyrosine production will also be investigated as the major mechanisms involved in vascular dysfunction leading to nanoparticle enhanced atherosclerosis. It is expected that nanoparticle toxicity will be influenced by a variety of exposure conditions including concentration, duration of exposure, and composition. This study will allow us to begin to understand the long-term exposure effects of nanoparticles on the cardiovascular system. The data obtained in the proposed animal studies can readily be used for extrapolation to occupational and ambient settings. In summary, the results from this proposal address a number of the research needs identified in this solicitation, including toxicity and exposure assessment. Ultimately, a systems approach will be developed to the understanding of nanomaterials toxicology sufficiently complete to allow predictions about health effects.