Waterpipe smoke condensate activates autophagy in non-tumorigenic lung epithelial cells: Implications for inflammation and stemness

Waterpipe smoking has emerged as a major global health concern, with incompletely characterized effects on bronchial epithelial cells. In this study, we investigated the cytotoxic and adaptive responses of non-tumorigenic human bronchial epithelial BEAS-2B cells exposed to waterpipe smoke condensate (WPSC). Increasing concentrations of WPSC reduced cell viability in a dose-dependent manner; however, exposure to 0.1% WPSC caused only a modest, transient reduction in viability that was no longer significant by 72 hrs and did not significantly induce apoptosis over 72 hrs, as determined by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and Annexin V/Propidium Iodide (PI) apoptosis assays. To elucidate the adaptive mechanisms underlying this resistance, we examined autophagic flux and found that WPSC induced time-dependent accumulation of LC3-II and p62, which was enhanced by bafilomycin A1 cotreatment, indicating the activation of autophagy. This was accompanied by increased phosphorylation of AMPK and decreased phosphorylation of mTORC1, consistent with an autophagy-mediated stress response. Functionally, the inhibition of autophagy with bafilomycin A1 increased apoptosis and necrosis, suggesting that autophagy could play a protective role. Moreover, WPSC exposure induced DNA damage, as evidenced by increased γH2AX and 53BP1 nuclear foci, and elevated proinflammatory cytokine expression (IL-1β and CCL2). Finally, WPSC treatment upregulated the expression of the cancer stem cell-associated markers CD44 and CD133. Collectively, our findings demonstrate that subcytotoxic exposure to waterpipe smoke activates autophagy in non-tumorigenic lung epithelial cells. This adaptive mechanism may represent an early cellular event linking waterpipe smoke exposure to lung carcinogenesis.