Plasma membrane damage triggered by benzalkonium chloride and cetylpyridinium chloride induces G0/G1 cell cycle arrest via Cdc6 reduction in human lung epithelial cells

Quaternary ammonium compounds, including benzalkonium chloride (BAC) and cetylpyridinium chloride (CPC), are widely used as disinfectants. Increased use of inhalable products containing BAC or CPC has raised concerns for lung toxicity. This study sought to elucidate the microstructure of plasma membrane damage caused by BAC and CPC and the subsequent mechanism by which the damage is mediated, as assessed using two human pulmonary epithelial cell lines (A549 and BEAS-2B). Scanning electron microscopic observation showed that exposure to BAC or CPC for 3 hr reduced the length and density of microvilli on the plasma membrane in A549 cells. Analysis of cell cycle distribution following plasma membrane damage revealed that BAC and CPC promote G0/G1 cell cycle arrest in both cell lines. The protein levels of Cdc6, an essential regulator of DNA replication during G1/S transition, are decreased significantly and dose dependently by BAC or CPC exposure. CPC and BAC decreased the Cdc6 levels that had been increased by a PI3K agonist in A549 cells, and levels of phosphorylated AKT were reduced in response to BAC or CPC. Conversely, exposure to equivalent concentrations of pyridinium chloride (lacking a hydrocarbon tail) induce no changes. These results suggest that plasma membrane damage triggered by BAC or CPC causes Cdc6-dependent G0/G1 cell cycle arrest in pulmonary cells. These effects are attributable to the long alkyl chains of BAC and CPC. The reduction of Cdc6 following plasma membrane damage may be caused, at least in part, by diminished signaling via the PI3K/AKT pathway.