Impact of Air Pollution in Airway Diseases: Role of the Epithelial Cells (Cell Models and Biomarkers)

Abstract

Biomedical research is multidisciplinary and often uses integrated approaches performing different experimental models with complementary functions. This approach is important to understand the pathogenetic mechanisms concerning the effects of environmental pollution on human health. The biological activity of the substances is investigated at least to three levels using molecular, cellular, and human tissue models. Each of these is able to give specific answers to experimental problems. A scientific approach, using biological methods (wet lab), cell cultures (cell lines or primary), isolated organs (three-dimensional cell cultures of primary epithelial cells), and animal organisms, including the human body, aimed to understand the effects of air pollution on the onset of diseases of the respiratory system. Biological methods are divided into three complementary models: in vitro, ex vivo, and in vivo. In vitro experiments do not require the use of whole organisms (in vivo study), while ex vivo experiments use isolated organs or parts of organs. The concept of complementarity and the informatic support are useful tools to organize, analyze, and interpret experimental data, with the aim of discussing scientific notions with objectivity and rationality in biology and medicine. In this scenario, the integrated and complementary use of different experimental models is important to obtain useful and global information that allows us to identify the effect of inhaled pollutants on the incidence of respiratory diseases in the exposed population. In this review, we focused our attention on the impact of air pollution in airway diseases with a rapid and descriptive analysis on the role of epithelium and on the experimental cell models useful to study the effect of toxicants on epithelial cells.

Keywords: airway diseases; environmental pollution; epithelial cells; exposome; system biology.

Figure 1

Effects of PBDE-47, -99, and -209 flame retardants in bronchial epithelial cells. PBDE-47, -99, and -209 cause DNA damage of epithelial cells and alter the activity of histone protein γ-H2AX in in vitro/ex vivo cell models of human bronchial epithelial cells.

Figure 2

Three-dimensional (3D) ALI cultures of epithelial cells (primary and cell line) to study the effects of environmental contaminants in airway disease. Steps to obtain primary epithelial cells from human tissue: (a) Collection of bronchial biopsies or surgical specimens; (b) epithelial cell processing: tissue was dissociated, resuspended in bronchial epithelial growth medium; (c) cell expansion and culture of epithelial cells; (d) the cells are seeded onto the microporous membrane pre-coated with collagen in submerged conditions until confluence and culture in ALI; (e) reaching the confluence, the cells begin to lift at the air–liquid interface starting the differentiation fed by the culture medium in the basolateral side. Hence, the epithelial cells differentiate in the pseudostratified phenotype and build a tissue such as the epithelium of the lung.

Figure 3

Two different 3D organ-typical cell cultures to study the effects of environmental contaminants in airway diseases of the lung. (a) Three-dimensional (3D) cell culture model obtained with a co-culture of epithelial cells and fibroblasts; (b) Three-dimensional (3D) cell culture model obtained with multiple cell types from the pulmonary system (structural and inflammatory). Three-dimensional (3D) tetraculture system containing macrophages, epithelial cells, fibroblasts, and endothelial cells, mimicking lung organization.

Figure 4

Cell-based in vitro lung models for the study of inhalation toxicity. Visual representation of three-dimensional in vitro models of each model system for the study of inhalation toxicity: (a) organoid culture and (b) microfluidic and microfabricated device culture. ECM, extracellular matrix.

Figure 5

The measurement of TEER in the 3D ALI culture stimulated with air pollutants such as PBDE-47, -99, and -209 modifies the integrity of the epithelium of the lung, promoting airway diseases. (a) Electrode useful to measure the values of TEER in 3D cell culture; (b) reduction of TEER values before and after the treatment with contaminants of epithelial cells cultured in ALI; (c) morphological changes of epithelial cells cultured in ALI; (d) the damage of integrity of 3D epithelium is associated with a reduction of ZO-1 expression.

Figure 6

Experimental approach to identify molecular biosensors of airway disease. “In vitro/ex vivo” studies obtained with experimental approach performed with 3D cell cultures of bronchial epithelial cells (cell line and primary cells); Integrated approach obtained including “in vitro”, ex vivo” 3D cell cultures of bronchial epithelial cells and “in vivo” studies.