Assessment of Alterations in Barrier Functionality and Induction of Proinflammatory and Cytotoxic Effects After Sulfur Mustard Exposure of an In Vitro Coculture Model of the Human Alveolo-Capillary Barrier

Abstract

Acute lung injury after sulfur mustard (SM) inhalation is characterized by massive, localized hemorrhage and alveolar edema, which implies severe disruption of the vascular and distal airway barrier. In this study, we tested a recently established in vitro coculture model of the alveolo-capillary barrier for its applicability to investigate acute toxic effects of SM at the human respiratory unit. The epithelial compartment of cocultures was exposed to varying concentrations of SM (0–1000 μ M; t = 30 min). Following exposure, functional and structural barrier integrity of cocultures was monitored over a period of 24 h. A 50% reduction of transbilayer electrical resistance (TER) within 12–24 h after exposure to 300 μ M SM and within 8 h after 1000 μ M SM revealed a time- and concentration-dependent impairment of barrier functionality, which was associated with structural loss of both cell layers. Subsequent quantification of interleukin (IL)-6 and IL-8 in cell culture supernatants of exposed cocultures showed enhanced liberation of proinflammatory markers. Highest mediator levels were detected after 300 μ M SM, with pronounced stimulation in the endothelial compartment. SM-related cytotoxicity was determined by assessing adenylate kinase (AK) release and by quantifying the fraction of DNA-fragmented nuclei using terminal deoxynucleotidyl transferase-mediated DNA nick-end labeling (TUNEL) and nuclear Hoechst staining. Both methods exposed a concentration-dependent increase of SM-mediated cytotoxic effects with high effects on endothelial cells. We conclude that the described in vitro model reflects important characteristics of SM-mediated acute lung injury in vivo and thus can be used to explore involved pathophysiological pathways.