Bioaerosols from a food waste composting plant affect human airway epithelial cell remodeling genes

Abstract

The composting procedure in food waste plants generates airborne bioaerosols that have the potential to damage human airway epithelial cells. Persistent inflammation and repair responses induce airway remodeling and damage to the respiratory system. This study elucidated the expression changes of airway remodeling genes in human lung mucoepidermoid NCI-H292 cells exposed to bioaerosols from a composting plant. Different types of microorganisms were detectable in the composting plant, using the agar culture method. Real-time polymerase chain reaction was used to quantify the level of Aspergillus fumigatus and the profile of remodeling genes. The real-time PCR results indicated that the amount of A. fumigatus in the composting hall was less than 10(2) conidia. The endotoxins in the field bioaerosols were determined using a limulus amebocyte lysate test. The endotoxin levels depended on the type of particulate matter (PM), with coarse particles (2.5-10 μm) having higher endotoxin levels than did fine particles (0.5-2.5 μm). After exposure to the conditioned medium of field bioaerosol samples, NCI-H292 cells showed increased pro-inflammatory interleukin (IL)-6 release and activated epidermal growth factor receptor (EGFR), transforming growth factor (TGF)-β1 and cyclin-dependent kinase inhibitor 1 (p21 WAF1/CIP1) gene expression, but not of matrix metallopeptidase (MMP)-9. Airborne endotoxin levels were higher inside the composting hall than they were in other areas, and they were associated with PM. This suggested that airborne bioaerosols in the composting plant contained endotoxins and microorganisms besides A. fumigatus that cause the inflammatory cytokine secretion and augment the expression of remodeling genes in NCI-H292 cells. It is thus necessary to monitor potentially hazardous materials from bioaerosols in food composting plants, which could affect the health of workers.

Figure 1

Layout of sampling pots of the food waste composting plant. The white color rea belongs an open access environment. The composting hall, maintenance, liquid fertilizer area, clean area, office and restaurant are closed building equipped with windows and ventilation system.

Figure 2

Distribution of microorganisms in the composting hall, maintenance and restaurant.

Figure 3

IL-6 secretion of NCI-H292 cells cultured with field bioaerosol samples. Confluent NCI-H292 cells (5 × 105) were individually cultured with the conditioned medium of field bioaerosol samples for 24 h. Asterisk indicated significant at p < 0.05 compared with the control group.

Figure 4

Quantitative expression of remodel genes in NCI-H292 cells treated with control group, standard A. fumigatus or field bioaerosol samples for 24 h. The bars were represented the mean fold change of mRNA expression between control group and treatment group at least three independent experiments. Asterisk indicated significant at p < 0.05 compared with the control group.

Figure 5

A possible mechanism of airway remodeling genes in response to bioaersol exposure in the composting hall. The atopic inflammation is triggered when innate immune cells of bronchial epithelial cells are exposed to bioaerosol allergens. The activation of IL-6 further recruits the inflammatory cells, and consequently programs epithelial cells to healing or remodeling. In addition, TGF-β1 activates EGFR phosphorylation and increases p21^WAF1/CIP1 expression that implicates airway remodeling due to irregular cell proliferation and prolonged repair duration. The unchanged MMP-9 expression might be compensated for the over-expression of STAT-3 and cyclin D-dependent kinase. Consequently, both the atopy reaction and ligand induced activation of EGFR signaling cascade are to tend toward to guide cells healing or remodeling.