Background Polypropylene is widely used in the manufacturing of medical masks. Studies have shown that polypropylene microplastics can trigger inflammatory cell infiltration and release of inflammatory factors, but there are few studies on whether they induce autophagy and participate in inflammation.

Objective To clarify the toxic effect of polypropylene nanoplastics (PP-NPs) on BEAS-2B cells and to explore the role and mechanism of autophagy in cell inflammatory responses and oxidative stress injury of BEAS-2B cells following PP-NPs exposure.

Methods In this study, zeta potential, particle size and morphology of PP-NPs were analyzed by dynamic light scattering (DLS) and scanning electron microscopy (SEM). BEAS-2B cells in the logarithmic growth stage were exposed to different concentrations of PP-NPs (0, 40, 80, 160, and 320 μg·mL⁻¹) for different time (12, 24, and 48 h), and cell viability was measured by CCK-8 assay. Changes in cell morphology were observed after Wright-Giemsa staining after 24 h exposure. Lactate dehydrogenase (LDH) release was measured using a biochemistry analyzer. Interleukin-6 (IL-6) levels were detected by chemiluminescent immunoassay. Intracellular reactive oxygen species (ROS) intensities and levels were assessed by fluorescence microscopy and flow cytometry after 2',7'-dichlorofluorescein diacetate (DCFH-DA) staining. Autophagy was observed by confocal microscopy following dansylcadaverine staining, and microtubule associated protein 1 light chain 3 II (LC3 Ⅱ) expression was measured by flow cytometry. Additionally, 3-methyladenine (3-MA) was used as an autophagy inhibitor. After pre-treating BEAS-2B cells with 3 mmol·L⁻¹ 3-MA, and then exposed to a pre-determined concentration of PP-NPs (160 μg·mL⁻¹), IL-6, LDH, ROS, and LC3 Ⅱ levels were measured, and LC3 Ⅱ/I and autophagy-related proteins (Beclin-1) were detected by Western blot.

Results The PP-NPs used in this study were spherical particles with a narrow size distribution, a zeta potential of -21.8 mV in aqueous solution, and good dispersion. Compared with the control group, the PP-NPs exposure reduced the viability of BEAS-2B cells in a certain concentration- and time-dependent manner (P<0.01), the reduction in cell number was significant, and enhanced autophagosome fluorescence intensity was observed. The expressions of LDH, IL-6, ROS, and LC3 Ⅱ in the PP-NPs treatment groups were significantly higher than those in the control group (P<0.01) and increased with the PP-NPs concentration. Compared with the PP-NPs treatment group at the same concentration, pre-treatment of BEAS-2B cells with autophagy inhibitor 3-MA significantly reduced ROS, LDH, IL-6, LC3 Ⅱ/Ⅰ, and Beclin-1 (P<0.01).

Conclusion PP-NPs can induce autophagy and promote inflammation in human lung epithelial cells, and 3-MA inhibition of autophagy can reduce intracellular ROS levels and inhibit release of inflammatory factors.