Investigating the inflammatory response to exposure of ultrafine TiO₂ particulate matter to HUVECs

Epidemiological studies have indicated that strong causal evidence exists to link the inhalation of particulate matter to the exacerbation of pathology in the cardiovascular system, ranging from myocardial infarction and atherosclerosis to direct cytotoxicity and inflammation. Ultrafine particles are ubiquitous in ambient air, in industrial sites, and in air pollution. When particles are inhaled, deposition can occur in the lungs, and the mechanisms of pathology have been well-studied. However, ultrafine particulate matter can translocate from the lungs into the bloodstream to circulate throughout the body (Choi et al. 2010).Contradictory evidence exists of inflammation and cytotoxicity that is caused from nanoparticle exposure to the endothelium. When endothelial cells (ECs) are adversely stimulated, they have been shown to secrete cytokines that mediate an inflammatory response. Currently, studies that quantitatively evaluated the secretion of pro-inflammatory cytokines from ECs upon nanoparticle exposure are not accounting for the aggregation that can occur between particles over time and, therefore, are likely exposing cells to a wider range of aggregated sizes. This study evaluates the inflammatory response from ECs after particle exposure, with acute attention devoted to controlling particle aggregation. Specifically, we introduce a protocol that exposes ECs to the particles in a transwell system, where we take advantage of the effects of gravitational settling to expose the ECs only to the smallest fraction of the particles that are in suspension. After 72 h in the transwell assay, we found that the inflammatory response between varying concentrations of particles mirrored the inflammatory response of the positive control of lipopolysaccharide (LPS). These results indicate that the inflammatory response may have a stronger relationship to the particle size than to the concentration of the particles in mass per volume.