Arsenic compromises conducting airway epithelial barrier properties in primary mouse and immortalized human cell cultures.

Arsenic is a lung toxicant that can lead to respiratory illness through inhalation and ingestion, although the most common exposure is through contaminated drinking water. Lung effects reported from arsenic exposure include lung cancer and obstructive lung disease, as well as reductions in lung function and immune response. As part of their role in innate immune function, airway epithelial cells provide a barrier that protects underlying tissue from inhaled particulates, pathogens, and toxicants frequently found in inspired air. We evaluated the effects of a five-day exposure to environmentally relevant levels of arsenic {<4µM [~300 µg/L (ppb)] as NaAsO2} on airway epithelial barrier function and structure. In a primary mouse tracheal epithelial (MTE) cell model we found that both micromolar (3.9 µM) and submicromolar (0.8 µM) arsenic concentrations reduced transepithelial resistance, a measure of barrier function. Immunofluorescent staining of arsenic-treated MTE cells showed altered patterns of localization of the transmembrane tight junction proteins claudin (Cl) Cl-1, Cl-4, Cl-7 and occludin at cell-cell contacts when compared with untreated controls. To better quantify arsenic-induced changes in tight junction transmembrane proteins we conducted arsenic exposure experiments with an immortalized human bronchial epithelial cell line (16HBE14o-). We found that arsenic exposure significantly increased the protein expression of Cl-4 and occludin as well as the mRNA levels of Cl-4 and Cl-7 in these cells. Additionally, arsenic exposure resulted in altered phosphorylation of occludin. In summary, exposure to environmentally relevant levels of arsenic can alter both the function and structure of airway epithelial barrier constituents. These changes likely contribute to the observed arsenic-induced loss in basic innate immune defense and increased infection in the airway.

VSD following blunt cardiac trauma: MRI findings.

In this report, we describe the clinical and radiographic findings of ventricular septal defects (VSDs) following blunt cardiac trauma in two patients. VSDs following either penetrating or blunt cardiac trauma are a rare occurrence. The variable presentation and timing of symptom onset along with the common association of other injuries can make the diagnosis of a posttraumatic VSD difficult. Therefore, investigation should be initiated when elements from the history and physical examination (e.g., new onset murmur), laboratory tests (e.g., cardiac enzymes), EKG, and CT or echocardiography warrant it. The first patient was a 19-year-old male who was hemodynamically stable on initial presentation to this trauma center after a motor vehicle collision. A posttraumatic VSD was found by echocardiography on the day of admission and further defined on cardiac MRI (CMRI). The second patient was a 31-year-oid male who presented after a high-speed motorcycle accident and was found to have a VSD 40 days later on CMRI after a fluctuating clinical course and multiple normal echocardiograms. Both patients had good outcomes with subsequent surgical closure.

Arsenic upregulates MMP-9 and inhibits wound repair in human airway epithelial cells.

As part of the innate immune defense, the polarized conducting lung epithelium acts as a barrier to keep particulates carried in respiration from underlying tissue. Arsenic is a metalloid toxicant that can affect the lung via inhalation or ingestion. We have recently shown that chronic exposure of mice or humans to arsenic (10-50 ppb) in drinking water alters bronchiolar lavage or sputum proteins consistent with reduced epithelial cell migration and wound repair in the airway. In this report, we used an in vitro model to examine effects of acute exposure of arsenic (15-290 ppb) on conducting airway lung epithelium. We found that arsenic at concentrations as low as 30 ppb inhibits reformation of the epithelial monolayer following scrape wounds of monolayer cultures. In an effort to understand functional contributions to epithelial wound repair altered by arsenic, we showed that acute arsenic exposure increases activity and expression of matrix metalloproteinase (MMP)-9, an important protease in lung function. Furthermore, inhibition of MMP-9 in arsenic-treated cells improved wound repair. We propose that arsenic in the airway can alter the airway epithelial barrier by restricting proper wound repair in part through the upregulation of MMP-9 by lung epithelial cells.