Effect of nonendocytic uptake of nanoparticles on human bronchial epithelial cells

The toxicity of artificial nanoparticles is a major concern in industrial applications. Cellular uptake of hard nanoparticles could follow either endocytic or nonendocytic pathways, leading to different stimuli to the cells. Yet the cellular responses to nanoparticles following different pathways have not been compared due to the lack of an independent nonendocytic delivery method. We applied a unique delivery method, nanochannel electroporation (NEP), to produce predominantly nonendocytic uptakes of quantum dots (Q-dots) and multiwalled carbon nanotubes (MWCNTs) with different chemical modifications. NEP delivery bypassed endocytosis by electrophoretic injection of nanoparticles into human bronchial epithelial (BEAS-2B) cells at different dosages. Conventional exposure by direct nanoparticle suspending in cell culture medium was also performed as control. The dosage-dependent responses to nanoparticles under different uptake pathways were compared. Fluorescence colocalization demonstrated that nanoparticles followed both endocytic and nonendocytic pathways for cell entry in contact exposure, whereas NEP delivery of nanoparticles bypassed endocytosis. Nonendocytic entry resulted in much higher oxidation stress and, for MWCNTs, more cell death in BEAS-2B cells. Despite the observation that most nanoparticles were taken up by cells through endocytosis, the minor nonendocytic entry of nanoparticles seemed to dominate the overall cellular response in conventional contact exposure. Our finding suggests that prevention against nonendocytic uptake could help reduce the toxicity of hard nanoparticles.