The role of reactive oxygen species as mediators of respiratory syncytial virus induced pulmonary inflammation
Respiratory Syncytial Virus (RSV) is the leading cause of epidemic respiratory tract illness in children worldwide. Although the mechanisms of RSV-induced airway disease are unknown, experimental evidence suggests that early local inflammatory processes serve as major initiating events in the pathogenesis of RSV-induced lung disease. RSV induced inflammation is mediated in part by small inflammatory chemokines. We investigated the mechanism of RSV-induced chemokine RANTES gene expression in epithelial cells and identified reactive oxygen species as critical signaling molecules involved in STAT and IRF transcription factor activation and the IKK-epsilon pathway, two activated pathways involved in the regulation of pro-inflammatory gene expression. We showed that RSV induced oxidative stress in vivo and that antioxidant therapy with butylated hydroxyanisole (BHA) attenuated RSV induced oxidative stress, pulmonary inflammation and airway hyper-responsiveness. The one caveat to anti-inflammatory antioxidant therapy was the slight increase in RSV viral load observed following antioxidant administration. To eliminate the undesired outcome of increased viral load, a combination therapy approach was utilized employing BHA and the potent anti-viral IFN-alpha. Combination therapy yielded similar results of diminishing RSV-induced pulmonary inflammation while also decreasing RSV viral load in the lungs. Another key mediator regulated by oxidative stress and involved in inflammation is Poly (ADP)-Ribose Polymerase (PARP). We demonstrated that RSV is a potent inducer of PARP activity and that pharmacological inhibition of PARP with INO-1001 abolished RSV-induced PARP activity. INO-1001 also significantly reduced RSV-induced release of inflammation and lung pathology. Of environmental significance, cigarette smoke is also a potent oxidant mixture and important risk factor for the severity of RSV-induced disease. The mechanism(s) causing a worsening of RSV-induced lung disease by environmental tobacco exposure are unclear. Therefore, we investigated the effect of co-exposure of airway epithelial cells to cigarette smoke condensate (CSC) and RSV on inflammatory chemokine gene expression. We demonstrated that CSC and RSV synergistically increased MCP-1 and IL-8 chemokine expression through NF-kappaB and IRF transcription activation. Overall, the modulation of RSV-induced oxidative processes, either by dampening ROS production through pharmacological intervention or by heightening it by toxicant exposure, identify ROS as major signaling molecules involved in regulating RSV-induced inflammation.