A new University of Michigan simulation shows that carbonaceous nanoparticles emitted by diesel engines and other combustion sources can get trapped in the lungs and inhibit the function of lung surfactant—a fluid that facilitates breathing.
Lung surfactant contains protein and lipid molecules. It reduces surface tension in the lungs, prevents them from collapsing and helps transport foreign particles that will ultimately be expelled from the lungs. Inhaled carbon nanoparticles, however, appear to behave differently than most foreign particles. Computer simulations indicated that they wouldn’t be expelled, but would become trapped in the surfactant, entangled with fatty lipid molecules that wrapped their “tails” around the nanoparticles and into their central cavities.
“The presence of the nanoparticle can hinder the function of lung surfactant by affecting the interaction between the lipids and peptides,” said Angela Violi, assistant professor in the departments of Mechanical Engineering, Chemical Engineering and Biomedical Engineering. Violi presented her findings during an invited talk at the American Chemical Society meeting in Philadelphia.
This is believed to be the first time researchers have demonstrated how these nanoparticles can get caught in the lungs and affect the behavior of surfactant. Other studies have shown that buildup of nanoparticles in the lungs can lead to inflammation, blood clotting and changes in breathing and heart rates.
There is mounting evidence that very small particles have a greater negative impact on health than larger particles. Nanoparticles emitted by diesel engines and other combustion sources are a health concern because of both their size and the carcinogens with which they are associated. This problem is exacerbated by the fact that there is currently no effective regulatory control of these nanoparticles.—Angela Violi
Current US and European diesel emissions regulations address particle sizes of 2.5 microns or larger (PM2.5, PM10)—up to three orders of magnitude larger than the nanoparticles Violi studies. Carbon nanoparticles make up only 0.1 to 1.5% of the total mass of particles diesel engines emit, but in terms of the number of particles, nanoparticles represent between 35% and 97% of the emissions, depending on the traffic.
The computer model Violi created to run this simulation can also predict how various combustible materials will burn, what nanoparticles will be created, how those particles will be shaped and how they could affect the lungs. This tool could be useful in predicting biofuel emissions, Violi says. “It could help us reach the goal of engineering biofuel molecules to reduce emissions,” Violi said. It’s conceivable that engineers could genetically modify plants to produce cleaner burning fuels, she said.
A related paper on this research titled “Molecular Dynamics Simulation Study of a Pulmonary Surfactant Film Interacting with a Carbonaceous Nanoparticle” will be published in the 15 Oct issue of Biophysical Journal.
Separately, a new review published in the 26 August issue of the Journal of the American College of Cardiology (JACC) highlights that unregulated ultrafine particles from tailpipe emissions may be translocated into the circulation and directly transported to the vasculature and heart where they can injure the heart and blood vessels, increase rates of hospitalization for cardiac illness, and can even cause death. Particulate pollution is categorized into three main classes: coarse particles with aerodynamic diameter (AD) 2.5 to 10 µm (PM10); fine particles (AD <2.5 µm; PM2.5), and ultrafine particles (AD <0.1 µm; UFPs). (Earlier post.)