Assessment of an in vitro model of lung epithelial cell stress responses

The ability of cells to adapt and survive environmental and physiological stress relies on activation of cellular stress responses. These include anti-oxidant, inflammatory and apoptotic responses. These cellular responses are mediated by cell signalling pathways, including those controlled by the transcription factors Nrf2 (antioxidant response) and NF-?ß (inflammatory response). As part of a suite of in vitro models for the comparison of different nicotine delivery products, an in vitro lung cell stress response model has been developed. Human bronchial epithelial cells were exposed to positive controls or cigarette smoke aqueous extracts (CSEaq) from 3R4F and 1R5F reference cigarettes for 4hours. Cellular responses were then measured as oxidative, pro-inflammatory, apoptotic and necrotic endpoints. Cellular oxidative stress was characterised by measurement of the intracellular glutathione ratio, intracellular ROS production and activation of the Nrf2-controlled Anti-oxidative Response Elements (ARE). The inflammatory response of the cells was determined through quantification of secreted cytokines, IL-1a, IL-6 and IL-8. Apoptotic and necrotic responses were characterised by measurements of Caspase 3/7 activity and live-cell protease activity. Stably transfected luciferase reporter cell lines were utilised to quantify the transcriptional control of anti-oxidant and inflammatory pathways. All cell stress response endpoints were activated by exposure to positive controls or CSEaq. The observed concentration-dependent lowering of the glutathione ratio and increase in intracellular ROS generation corresponded with an increase in Nrf2 transcriptional activation of the ARE. It has been demonstrated that this model was able to distinguish between CSEaq from the two different reference cigarettes. We propose that this model may be suitably sensitive for biological comparisons of cigarettes against different nicotine delivery products.