Fig. 3

Nicotine treatment mitigates MPP⁺-induced apoptosis in HEK293T cells. a Safety evaluation of nicotine using the Cell Counting Kit-8 (CCK 8) assay. n = 6 in each group. b Damage assessment of MPP⁺ using the CCK8 assay. n = 6 in each group. c Improvement in cell viability owing to nicotine treatment is concentration dependent. n = 6 in each group. d The bright field and live/dead staining images of different treatment groups. Scale bar = 100 μm. e, f Apoptotic flow cytometry and quantitative analyses of the apoptotic cell percentage. n = 3 in each group. g Transmission electron microscopy images of HEK293T cells. The phagosome (red triangle labelled) in the nicotine only treated group indicates engulfment of small molecules, and the HEK293T cells of the nicotine + MPP⁺ group are intact. MPP⁺ treated HEK293T cells manifest early apoptosis accompanied by nuclear fragmentation, condensation, and membrane integrity. These cells show ruptured membranes and the disappearance of normal cellular structures during late apoptosis. Scale bar = 5 μm. Significant differences are shown by *p < 0.05, **p < 0.01, ***p < 0.001