Chlorine exposure induces Caspase-3 independent cell death in human lung epithelial cells

Chlorine (Cl₂) is a common toxic industrial gas and human inhalation exposure causes tissue damage with symptoms ranging from wheezing to more severe symptoms such as lung injury or even death. Because the mechanism behind Cl₂-induced cell death is not clearly understood, the present study aimed to study the cellular effects in vitro after Cl₂ exposure of human A549 lung epithelial cells. In addition, the possible treatment effects of the anti-inflammatory antioxidant N-acetyl cysteine (NAC) were evaluated. Exposure of A549 cells to Cl₂ (100-1000 ppm) in the cell medium induced cell damage and toxicity within 1 h in a dose-dependent manner. The results showed that 250 ppm Cl₂ increased cell death and formation of apoptotic-like bodies, while 500 ppm Cl₂ exposure resulted in predominantly necrotic death. Pre-treatment with NAC was efficient to prevent cell damage at lower Cl₂ concentrations in part by averting the formation of apoptotic-like bodies and increasing the expression of the anti-apoptotic proteins clusterin and phosphorylated tumour protein p53(S46). Analysis showed that Cl₂ induced cell death by a possibly caspase-independent mechanism, since no cleavage of caspase-3 could be detected after exposure to 250 ppm. Currently, these results justifies further research into new treatment strategies for Cl₂-induced lung injury.