Exposure to Hog Dust Extract Decreases Barrier Integrity in Caco‐2 Cells, Induces Airway Inflammation and Increases Intestinal Permeability in Mice

Abstract

Agricultural enterprises, such as concentrated animal feeding operations (CAFOs), are responsible for the production of 10% of global greenhouse gases and harmful environmental pollutants including hydrogen sulfide, ammonia and particulate matter. Seasonal farm workers, especially swine farmers, are frequently exposed to organic dust that is pro-inflammatory in the lung and are thus at greater risk of developing pneumonia, asthma and other respiratory conditions. In addition to respiratory disease, these air pollutants are directly associated with altered gastrointestinal (GI) physiology and the development of GI diseases. Therefore, the aim of the current study was to identify mechanisms by which extracts of dusts derived from hog CAFOs (HDE) can disrupt intestinal homeostasis. Caco-2 BBE monolayers were seeded at 0.5x106cells/well in a Transwell system and exposed to a single dose of either 0.25%, 0.5%, 0.75%, 1% or 5% HDE. A decreasing trend was seen in monolayer integrity, determined by transepithelial electrical resistance (TEER), at 24-and 48-hours following treatment with 5% HDE (Two-Way ANOVA, p=0.1824 and p=0.2017, respectively, n=3). Moreover, 8-week-old male or female C57BL/6 mice (n=12) were intranasally exposed to saline (n=6) or 12.5% HDE (n=6) for 3 weeks. Bronchoalveolar lavage fluid from HDE-treated mice showed no changes in macrophage cell numbers (unpaired t-test, p=0.2993), but exhibited elevated total cell and neutrophil levels (unpaired t-test, p=0.0027 and p=0.0061, respectively) in comparison to saline controls. Furthermore, no significant differences were seen among the colon lengths of HDE-treated mice (8.32 ± 0.13cm SEM) to that of saline controls (9.2 ± 0.67cm SEM). Additionally, HDE increased permeability to FITC-dextran 4kDA and rhodamine B-dextran 70kDA (unpaired t-test, p<0.001). Moreover, histological changes observed by hematoxylin and eosin staining indicated epithelial cell loss and minimal-mild inflammation in the proximal and distal colon of HDE-treated mice. Together, these findings suggest that airway exposure to CAFOs dusts promotes airway inflammation and can access the gastrointestinal tract to increase regulated and/or unrestricted intestinal permeability, possibly due to intestinal epithelial cell damage. Further identification of mechanistic interactions between the respiratory and gastrointestinal systems is imperative to understand the complex physiological consequences of chronic exposure to organic dusts derived from CAFOs on the gut-lung axis.