Micro- and nanoplastics with diverse sizes and chemical structures compromise barrier integrity, cause extensive epithelial cell injury, and induce oxidative and endoplasmic reticulum stress

Plastic pollution is an escalating global crisis, and growing evidence suggests that microplastics can accumulate in various biological systems. This study comprehensively examined the effects of microand nanoplastic particles of varying sizes and chemical structures on human gut epithelial cells, peripheral blood mononuclear cells (PBMCs), and nasal organoids. We used commercially available polyethylene particles (1–4 μm), polystyrene (PS) particles with diameters of 0.17 μm, 1–1.4 μm, 4.8–5.8 μm, and 9.5–11.5 μm as well as polyethylene terephthalate (PET) particles developed in-house. A microfluidic gut-on-a-chip system was employed to create a tubular barrier using Caco-2 cells. Epithelial barrier integrity was assessed via transepithelial resistance measurements and paracellular flux assay. Cell viability was evaluated using propidium iodide staining in flow cytometry, and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assays, and cell proliferation was analyzed through ³H-thymidine incorporation. In addition, 2′,7′–dichlorofluorescin diacetate (DCFDA) assay was used to determine reactive oxygen species (ROS) levels in Caco-2 and airway cell lines. We performed RNA-seq and targeted proteomics to investigate the effects of microplastics at the molecular level. Smaller-diameter PS particles induced significant cell death even at lower doses. PS (0.17 μm, 1–1.4 μm) and PET impaired epithelial integrity in both gut-on-a-chip and nasal organoids, with PET disrupting the barrier even at low exposure levels (<1000 particles/mL). Upregulated genes were primarily associated with apoptosis, endoplasmic reticulum (ER) stress, and oxidative stress. Notably, ATF4, CHOP, and GRP78 exhibited increased expression at higher PET microplastic concentrations, suggesting that sustained ER stress, induced by protein misfolding, intersects with oxidative stress pathways, ultimately triggering apoptotic cascades. Interestingly, PET, a widely used plastic in daily life, exhibited a recurring pattern that its elevated concentrations induced canonical stress-response elements (NQO1, SOD2, HSPA1B, FOXO3) alongside apoptotic effectors (Bax, CASP3, TRAIL). Higher doses of PS and PET also led to significantly remarkable changes in the targeted proteomics. In conclusion, our results highlight the multifaceted nature of microplastic-induced damage, characterized by impaired barrier function, reduced cellular viability, and widespread transcriptional shifts converging on oxidative stress, ER stress, and programmed cell death pathways.