The heated tobacco product (HTP) iQOS is gaining more and more popularity worldwide, due to the industry claims of reduced toxicity. HTPs are considered less harmful than combustible cigarettes (CCs) due to the reduced levels of toxic compounds in their mainstream emissions. However, little is known about iQOS impact on human health, and literature is missing a systematic approach to compare cigarette and iQOS health effects on lung in vitro models.

The alveolar cell line A549 was exposed to CCs or iQOS emissions in form of liquid extracts. Cells were exposed for 24 hours in conditioned media, containing different percentages (vol/vol) of CC or iQOS extracts. The toxicological potential of CC and iQOS extracts were investigated by measuring cytotoxicity and cell death, release of reactive oxygen species (ROS) and gene expression differences.

1% cigarette and 1% iQOS extracts induced highly similar cytotoxic responses, statistically significantly higher than in unexposed cells. A549 exposed to 1% and 2% cigarette and iQOS extracts displayed higher levels of ROS than control samples, but no dose-response effects were observed. The biological processes autophagy, mitophagy and mitochondrial biogenesis were similarly impaired in CC and iQOS-exposed cells compared to unexposed controls. Moreover, the expression of mitochondrial membrane complexes and various other genes involved in energy metabolism were equally reduced in exposed cells.

In this study, no significant differences in the toxicological impacts of CC and iQOS extracts were observed in differently exposed A549 cells. Both liquid extracts increased cell death and ROS release, and impaired gene expression of exposed cells. As the present study suggests similar health impacts of cigarette and iQOS on A549 cells, the industry claims of reduced toxicity should be re-evaluated accordingly. Future investigations involving more advanced in vitro models and exposure setups will better clarify the health impacts of HTPs on lung homeostasis.