It has become widely acknowledged that a pulmonary particulate exposure has adverse effects beyond the lungs and can exert an important influence on the cardiovascular system, but pathological mechanisms to explain extrapulmonary insult remain unclear. We propose that serum carries an as yet unknown "inflammatory potential", possibly consisting of degradation byproducts, adducted or modified endogenous proteins, or other modified components, that affects a pathological bioactivity which can be assessed using endothelial cells as biosensors. To confirm the phenomenon of serum inflammatory potential related to nanoparticulate exposures, we characterized a number of responses induced by serum from mice exposed to MWCNTs by pulmonary aspiration (0, 10, 40 ug/mouse) and inhalation (5 h/d x 19 d of 0.05, 0.5, and 5.0 mg/m3), with serum collected 4h and 24h after exposures. Primary mouse cerebrovascular endothelial cells treated with serum from exposed mice showed consistent elevation of adhesion molecules ICAM and VCAM, both in terms of relative mRNA and cell surface expression. Additionally, genomic assessment of treated endothelial cells revealed a panel of Toll-like receptor- and NF-kappaB-related responses upregulated, relative to cells treated with serum from control mice. Cell growth and proliferation pathways were downregulated, which mirrored functional outcomes of an in vitro scratch assay. Serum from MWCNT exposed mice also impaired ATP-stimulated endothelial nitric oxide synthesis, as measured by spin-trap electron paramagnetic resonance. Findings from aspiration studies were generally supported by results from sub-chronic inhalation exposures. These outcomes indicate the presence of pathological bioactive constituents in the serum following exposure to MWCNTs. The nature of these components remains unclear, but conventional inflammatory cytokines do not appear to be primary regulators. Future research to characterize the complete chemical and biological mixture of serum, linked to adverse bioactivity, is needed to better understand the extrapulmonary effects of inhaled toxicants. The findings of bioactivity in the serum may help explain many extrapulmonary outcomes related to inhaled nanoparticles and other toxicants.
Pulmonary-function; Pulmonary-system; Pulmonary-system-disorders; Particulates; Exposure-levels; Risk-factors; Lung; Lung-disorders; Lung-function; Cardiovascular-system; Pathology; Pathogens; Proteins; Cell-function; Cellular-function; Animals; Laboratory-animals; Toxins; Respiratory-system-disorders; Nanotechnology