Lysosomal changes caused by nicotine exposure in human epithelial tongue cells

Nicotine is an addictive substance and has been associated with several harmful effects on health. Many previous studies have focused on the receptor-mediated mechanisms of nicotine. However, non-receptor mediated effects of nicotine, such as effects on the lysosomes have also been reported. Well-functioning lysosomes are essential for cellular degradation pathways like the autophagic, phagocytic, and endocytic pathways. This study aimed to investigate nicotine's direct effect on lysosomes and lysosome-dependent activities in vitro. Cells from the immortalized human epithelial tongue cell line PE/CA-PJ49 were exposed to nicotine (5 mM) alone or in combination with bafilomycin A1 (10 nM; an inhibitor of lysosomal activity). Cell viability was measured using the MTT assay. Morphological changes were studied in a phase contrast microscope. Lysosomal activity was measured using flow cytometry and western blotting was used to quantify selected autophagy-related proteins. Only nicotine in combination with bafilomycin A1 resulted in decreased cell viability. However, morphological changes (vacuolization) were only observed in the cells exposed to nicotine. Apart from control, all exposures decreased lysosomal activity and increased the levels of the autophagy-related proteins p62/SQSTM1 and LC3-II. In conclusion, nicotine caused cellular vacuolization, reduced lysosomal activity, and increased levels of autophagy-related proteins indicating impaired autophagic flux.