IL-8 production by macrophages is synergistically enhanced when cigarette smoke is combined with TNF-α

Macrophages are key inflammatory cells in chronic obstructive pulmonary disease (COPD). The pathophysiology of cigarette smoke-induced lung emphysema is complex but there is a clear role for reactive oxygen species (ROS, such as peroxynitrite), tumor necrosis factor (TNF-α) and interleukin (IL)-8. We investigated whether TNF-α or cigarette smoke medium (CSM) alone or in combination induces the production of IL-8 by human macrophages or monocyte lymphoma U937. CSM and TNF-α induce a dose- and time-dependent increase in IL-8 production. Interestingly, when sub-threshold concentrations of CSM and TNF-α were co-incubated, a 1500% increase in IL-8 production was observed compared to either of the compounds alone. Similar results were obtained with TNF-α and the peroxynitrite donor SIN-1. Moreover, the overproduction of IL-8 was associated with an enhanced increase in the translocation of NF-κB and an enhanced decrease in glutathione levels. Preincubation of the cells with antioxidants, such as N-acetyl-l-cysteine (NAC), prevented the overproduction of IL-8 and activation of NF-κB. In conclusion, CSM exposure of macrophages up-regulates the expression and the production of IL-8 via reactive oxygen species and NF-κB activation. Moreover, CSM dramatically enhances the production of IL-8 in combination with TNF-α. Based upon the strong synergistic action, a combination therapy directed against ROS and TNF-α could be a new approach to stop the progression in lung damage during emphysema. © 2009 Elsevier Inc. All rights reserved.