Increased levels of several cytokines, which are biomarkers of inflammation, were also reported in the lung tissue exposed to conventional cigarette smoke.
In this study, scientists at British American Tobacco used an innovative systems-biology-based approach to examine the difference in gene and protein expression between lung cells exposed to smoke and those exposed to the test e-cigarette vapour. They found that human lung tissue exposed to cigarette smoke exhibits changes in gene and protein expression consistent with immune response, oxidative stress and inflammation. By contrast, the same responses were not observed following exposure to test e-cigarette vapour in this study.
Systems biology is a relatively new approach that combines biology and computational analysis to model the complex workings of biological systems.
Changes in gene expression are important because genes contain the instructions that ensure normal cell function. Genes are subsets of DNA, which contains the genetic instructions to create proteins that go on to perform essential functions as, for example, enzymes, hormones and receptors.The protein-making process involves a flow of genetic information from DNA to RNA molecules to protein: ‘DNA makes RNA makes protein’. In the study, scientists used state-of-the-art ‘next generation sequencing’ of RNA and other tests to identify any disturbance to the process that would signal changes in gene or protein expression.
‘Next generation sequencing is revolutionizing and expanding the frontiers of genomic research by offering faster, more detailed and accurate tools to unravel the genetic information from any biological system,’ explains Dr Marianna Gaca, Pre-clinical Assessment Manager at British American Tobacco.
An aerosol exposure system was used to compare the impact of cigarette smoke (from reference cigarette 3R4F) and e-cigarette vapour from Vype ePen, a commercially available e-cigarette. The exposure system contained human lung tissue – MucilAir™ – which is made up of human airway cells that have been cultured to form various different cell types that make up the lining of the respiratory tract.
The cells were exposed to smoke or vapour for 5 minutes at a time with a 30-minute break in between each exposure, over a period of 2 hours and 20 minutes to better mimic human use behaviour. The cells were allowed to rest for 24 hours and 48 hours following exposure, to allow any treatment-related effects to occur.
Cytotoxicity tests showed all cells to be viable. RNA sequencing and observations of changes in protein production revealed that the human lung cells exposed to cigarette smoke exhibit higher number of gene expression changes compared to e-cigarette vapour. The key biological functions affected by cigarette smoke were immune responses, oxidative stress and inflammation, which were not observed on exposure to e-cigarette vapour.
The results are published in Applied In Vitro Toxicology as part of a special issue on Next Generation Nicotine Products.
Banerjee, A., Haswell, L., Baxter, A., Parmar, A., Azzopardi, D., Corke, S., Thorne, D., Adamson, J., Mushonganono, J., Gaca, M., Minet, E. Differential Gene Expression Using RNA Sequencing Profiling in a Reconstituted Airway Epithelium Exposed to Conventional Cigarette Smoke or Electronic Cigarette Aerosols . Applied In Vitro Toxicology. Februrary 2017, ahead of print. doi:10.1089/aivt.2016.0024.