Aeroparticles, Composition, and Lung Diseases

Abstract

Urban air pollution is a serious worldwide problem due to its impact on human health. In the past 60 years, growing evidence established a correlation between exposure to air pollutants and the developing of severe respiratory diseases. Recently particulate matter (PM) is drawing more public attention to various aspects including historical backgrounds, physicochemical characteristics, and its pathological role. Therefore, this review is focused on these aspects. The most famous air pollution disaster happened in London on December 1952; it has been calculated that more than 4,000 deaths occurred during this event. Air pollution is a complex mix of gases and particles. Gaseous pollutants disseminate deeply into the alveoli, allowing its diffusion through the blood-air barrier to several organs. Meanwhile, PM is a mix of solid or liquid particles suspended in the air. PM is deposited at different levels of the respiratory tract, depending on its size: coarse particles (PM10) in upper airways and fine particles (PM2.5) can be accumulated in the lung parenchyma, inducing several respiratory diseases. Additionally to size, the composition of PM has been associated with different toxicological outcomes on clinical and epidemiological, as well as in vivo and in vitro animal and human studies. PM can be constituted by organic, inorganic, and biological compounds. All these compounds are capable of modifying several biological activities, including alterations in cytokine production, coagulation factors balance, pulmonary function, respiratory symptoms, and cardiac function. It can also generate different modifications during its passage through the airways, like inflammatory cells recruitment, with the release of cytokines and reactive oxygen species (ROS). These inflammatory mediators can activate different pathways, such as MAP kinases, NF-κB, and Stat-1, or induce DNA adducts. All these alterations can mediate obstructive or restrictive respiratory diseases like asthma, COPD, pulmonary fibrosis, and even cancer. In 2013, outdoor air pollution was classified as Group 1 by IARC based on all research studies data about air pollution effects. Therefore, it is important to understand how PM composition can generate several pulmonary pathologies.

Keywords: COPD; air pollution; asthma; fibrosis; inflammation; particulate matter.

Figure 1

Particulate matter and its atmospheric dynamics. Particles nucleation is generated by gases emission. Condensation can occur by cooling, producing particles. The interaction between primary particles and secondary particles constitute the coagulation. In this way, the particles can increase their size and composition.

Figure 2

Size and Dynamic of particles in the lung and other tissues. Large particles can be deposited in upper airways through sedimentation or impaction while in the lower airways Brownian diffusion can deposit them in the alveoli. Ultrafine particles can translocate to blood-circulating and be deposited in the liver, spleen or brain, although they might also penetrate through trans-synaptic mechanisms.

Figure 3

The principal route of damage after PM exposure.