Heated tobacco product emissions induce DNA damage in human bronchial epithelial cells via radical formation

IQOS is a heated tobacco product (HTP) claimed to be less harmful than regular cigarettes. It is unknown whether IQOS emissions contain radicals, cause DNA damage or affect the expression of DNA repair markers in human bronchial epithelial cells. This has important implications as IQOS diffusion is quickly growing, but little toxicological and genotoxic information on its emissions is available. Therefore, we determined the presence of radicals in cigarette smoke extract (CSE) and IQOS extract (IQOSE) by Electron Spin Resonance (ESR) spectroscopy and measured their levels of Tobacco-Specific Nitrosamines (TSNAs) with liquid chromatography-mass spectrometry (LC-MS). Next, DNA damage induced by CSE and IQOSE was determined by means of the Fpg-modified comet assay in human bronchial epithelial cells (BEAS-2B). Finally, the mRNA and protein levels of DNA repair markers in response to both extracts were evaluated. CSE contained significantly more reactive oxygen species (ROS) and TSNAs, whereas more carbon/nitrogen-centered radicals were detected in IQOSE. After 1 h exposure, 3%CSE and 5%IQOSE caused DNA oxidation, while 5%IQOSE also induced DNA strand breaks and alkali-labile sites. Exposure of cells to 1% and 3% IQOSE for 4 h upregulated the expression of DNA repair genes, whereas no significant impact on DNA repair protein levels was observed. This study shows that IQOS extract contains significant amounts of radicals and TSNAs, can induce DNA damage and increase the expression of DNA repair genes in human bronchial epithelial cells. Whether IQOS use is associated with higher risk of developing lung cancer remains to be determined.