The functions of cholera toxin subunit B as a modulator of silica nanoparticle endocytosis

The gastrointestinal tract is the main target of orally ingested nanoparticles (NPs) and at 9 the same time exposed to noxious substances, such as bacterial components. We investigated the 10 interaction of 59 nm silica (SiO2) NPs with differentiated Caco-2 intestinal epithelial cells in the pres-11 ence of cholera toxin subunit B (CTxB) and compared the effects to J774A.1 macrophages. CTxB can 12 affect cellular functions and modulate endocytosis via binding to the monosialoganglioside (GM1) 13 receptor, expressed on both cell lines. After stimulating macrophages with CTxB, we observed no-14 table changes in the membrane structure but not in Caco-2 cells and no secretion of the pro-inflam-15 matory cytokine TNF-α was detected. Cells were then exposed to 59 nm SiO2 NPs and CtxB sequen-16 tially and simultaneously, resulting in a high NPs uptake in J774A.1 cells but no uptake in Caco-2 17 cells was detected. Flow cytometry analysis revealed that exposure of J774A.1 cells to CTxB resulted 18 in a significant reduction in the uptake of SiO2 NPs. In contrast, the uptake of NPs by highly selective 19 Caco-2 cells remained unaffected following CTxB exposure. Based on colocalization studies, CTxB 20 and NPs might enter cells via shared endocytic pathways, followed by their sorting into different 21 intracellular compartments. Our findings provide new insights into the CTxB function to modulate 22 SiO2 NPs uptake in phagocytic but not in differentiated intestine cells.