Inhibition of caspase-dependent mitochondrial permeability transition protects airway epithelial cells against mustard-induced apoptosis

In the present study, the toxicity of yperite, SM, and its structural analogue mechlorethamine, HN2, was investigated in a human bronchial epithelial cell line 16HBE. Cell detachment was initiated by caspase-2 activation, down-regulation of Bcl-2 and loss of mitochondrial membrane potential. Only in detached cells, mustards induced apoptosis associated with increase in p53 expression, Bax activation, decrease in Bcl-2 expression, opening of the mitochondrial permeability transition pore, release of cytochrome c, caspase-2, -3, -8, -9 and -13 activation and DNA fragmentation. Apoptosis, occurring only in detached cells, could be recognized as anoikis and the mitochondrion, involved both in cell detachment and subsequent cell death, appears to be a crucial checkpoint. Based on our understanding of the apoptotic pathway triggered by mustards, we demonstrated that inhibition of the mitochondrial pathway by ebselen, melatonin and cyclosporine A markedly prevented mustard-induced anoikis, pointing to these drugs as interesting candidates for the treatment of mustard-induced airway epithelial lesions.