Effects of Th-1 and Th-2 Cytokines and Reactive Oxygen Species on Normal Human Bronchial Epithelial Cells

Epithelial damage and shedding of the epithelium are common observations in many airway diseases such as asthma, Sjögren’s syndrome, chronic obstructive pulmonary disease and cystic fibrosis. The ability of the cells to attach to each other and/or to the matrix seems to be altered. In the present study, cultured normal human bronchial epithelial cells were used as a model system. The desmosomes and also the focal adhesions were investigated to see if changes in these structural components as well as metabolic alterations could explain the observed shedding of the epithelium. Inflammatory mediators such as tumor necrosis factor alpha (TNF-α), interferon gamma (IFN-γ), interleukin-1 beta (IL-1β), interleukin-4 (IL-4), interleukin-5 (IL-5), interleukin-13 (IL-13), hypochlorous acid (HOCl) and nitric oxide (NO) are present in increased amounts in inflammation. The Th-1 cytokines, IFN-γ and TNF-α, as well as HOCl and NO affected the number of desmosomes and their ability to attach to each other. Interestingly, the Th-2 cytokines IL-4, IL-5 and IL-13 did not affect the cell-cell adhesion. HOCl and NO also affected the focal adhesions of the cells. Both morphological and functional studies indicated that TNF-α, IFN-γ, HOCl and NO affect the mitochondria. A decreased glucose oxidation rate could result in a decreased production of ATP, which in turn could lead to inhibition of many cellular activities including an impaired ability of the ciliary activity in bronchial epithelial cells and mucus transport. The antioxidant N-acetyl-L-cysteine and the nitric oxide synthase inhibitor N-propyl-L-arginine inhibited these effects of HOCl. This indicates that HOCl can induce damage both by induction of free radicals and also through an increased production of NO. TNF-α and IFN-γ also induced an increased production of NO. Nω-monomethyl-L-arginine reduced the cytokine-induced production of NO. The NO donor DETA NONOate reduced the total protein biosynthesis as well as the DNA content. NO can react with superoxide anions generated by inflammatory cells in the airways to form peroxynitrite ions, which in turn could generate hydroxyl radicals. These toxic ions may contribute to damage of the airway epithelial cells. In conclusion, pro-inflammatory cytokines such as TNF-α, IFN-γ and also the reactive oxygen species HOCl and NO could contribute to airway epithelial shedding by affecting the adhesion properties of the epithelial cells. More generalized morphological and metabolic changes could be other contributing factors, together with the increased production of NO