Particle-induced pulmonary acute phase response correlates with neutrophil influx linking inhaled particles and cardiovascular risk

BACKGROUND: Particulate air pollution is associated with cardiovascular disease. Acute phase response is causally linked to cardiovascular disease. Here, we propose that particle-induced pulmonary acute phase response provides an underlying mechanism for particle-induced cardiovascular risk. METHODS: We analysed the mRNA expression of Serum Amyloid A (Saa3) in lung tissue from female C57BL/6J mice exposed to different particles including nanomaterials (carbon black and titanium dioxide nanoparticles, multi- and single walled carbon nanotubes), diesel exhaust particles and airborne dust collected at a biofuel plant. Mice were exposed to single or multiple doses of particles by inhalation or intratracheal instillation and pulmonary mRNA expression of Saa3 was determined at different time points of up to 4 weeks after exposure. Also hepatic mRNA expression of Saa3, SAA3 protein levels in broncheoalveolar lavage fluid and in plasma and high density lipoprotein levels in plasma were determined in mice exposed to multiwalled carbon nanotubes. RESULTS: Pulmonary exposure to particles strongly increased Saa3 mRNA levels in lung tissue and elevated SAA3 protein levels in broncheoalveolar lavage fluid and plasma, whereas hepatic Saa3 levels were much less affected. Pulmonary Saa3 expression correlated with the number of neutrophils in BAL across different dosing regimens, doses and time points. CONCLUSIONS: Pulmonary acute phase response may constitute a direct link between particle inhalation and risk of cardiovascular disease. We propose that the particle-induced pulmonary acute phase response may predict risk for cardiovascular disease

Scanning electron microscope images of CNTs on powder form.

<p>A) MWCNT; B) SWCNT₁, and C) SWCNT₂.</p

Relative <i>Saa3</i> mRNA levels in lung and liver tissue after pulmonary deposition of particles by inhalation.

<p><i>Saa3</i> mRNA levels were normalised to 18S and multiplied by 10⁷. Mean±SD is shown. ^* p<0.05, ^†p<0.01, ^‡p<0.001, ^§One outlier has been removed in each group.</p

The correlation between the pulmonary mRNA expression of <i>Saa3</i> and the influx of neutrophils.

<p>The mRNA levels of <i>Saa3</i> correlated closely with the number of neutrophils across exposure type, dose, time after exposure and particle type.</p

Dose-response effects in mice 1, 3 and 28 days after intratracheal instillation of MWCNT.

<p>A) Pulmonary <i>Saa3</i> mRNA expression level; B) Hepatic <i>Saa3</i> mRNA expression level, C) SAA3 concentration in BALF, and D) SAA3 protein in plasma. *, **, ***: Statistically significant compared to control mice at the 0.5, 0.01 and 0.001 level, respectively.</p

Overview of studies and nanomaterials.

*<p>Based on a deposition fraction similar to NanoTiO₂,^† Mean diameter (number distribution) from National Institute of Standards and Technology, Certificate of Analysis, Standard Reference Material® 2975,^‡ Geometric mean, ^§ Not detetermined, ^? Hydrodynamic size, ^** Study 2 was an additional experiment performed to obtain plasma from MWCNT instilled mice and control animals.</p

Relative <i>Saa3</i> mRNA levels in lung and liver tissue after pulmonary deposition of particles.

<p><i>Saa3</i> mRNA levels were normalised to 18S and multiplied by 10⁷. Mean±SD is shown. * p<0.001 compared to controls. ^† Not determined.</p

Normalised <i>Saa3</i> mRNA levels in lung 1, 3 and 28 days after pulmonary exposure to nanomaterials by instillation (study 1).

<p><i>Saa3</i> mRNA levels were normalised to 18S and multiplied by 10⁷. Mean±SD is shown.</p>*<p>p<0.05, †p<0.01, ‡p<0.001, §Data published previously <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0069020#pone.0069020-Bourdon1" target="_blank">[21]</a>.</p