Polystyrene nanoplastics compromise oral epithelial barrier integrity and alter tight junction-related protein organization in TR146 human buccal epithelial cells

The pervasive environmental presence of nano- and microplastics, particularly polystyrene nanoplastics (PSNPs), has raised increasing concern regarding their potential adverse effects on human health. While epithelial barrier impairment is recognized as a critical toxicological outcome, the oral epithelium remains a poorly understood target despite being the primary gateway for ingested nanoplastics. In this study, we demonstrate that PSNPs induce significant functional impairment of the oral barrier even under sub-cytotoxic conditions (>80% cell viability). Exposure of TR146 human buccal epithelial cell layers to PSNPs triggered an early increase in paracellular permeability (fluorescein isothiocyanate-labeled dextran (4 kDa) flux), followed by a decline in transepithelial electrical resistance. Crucially, these functional deficits occurred in the absence of overt cytotoxicity and were associated with the molecular downregulation and altered distribution of tight junction-related proteins, including ZO-2, occludin, MarvelD3, and claudin-3 and claudin-4. Our findings indicate that PSNP-induced alterations in TJ-related protein distribution may represent an early molecular event associated with oral epithelial barrier dysfunction under sub-cytotoxic conditions. Collectively, this study highlights the oral epithelium as a highly sensitive target and underscores that functional barrier failure, rather than direct cytotoxicity, may represent a key mechanism underlying nanoplastic-associated toxicity.