Cellular uptake mechanism and intracellular fate of hydrophobically modified pullulan nanoparticles

The cellular uptake mechanism and intracellular fate of self-assembled nanoparticles (NPs) of cholesterol-modified pullulan (CHSP) by human hepatocellular carcinoma (HepG2) cells were investigated. Covalent conjugation with fluorescein isothiocyanate (FITC) yielded stably labeled CHSP (FITC-CHSP), which was successfully formulated into NPs (mean particle size 63.0 ± 1.9 nm) by dialysis. A cytotoxicity assay clearly indicated that the CHSP NPs did not show significant toxicity in HepG2 cells. The effects of NP concentration, incubation time, and temperature on the cellular uptake of the NPs were systematically evaluated by fluorometry, and the results suggested that cellular uptake of the NPs was concentration-,time-, and temperature-dependent. In vitro experiments with endocytic inhibitors revealed that clathrin-mediated endocytosis and macropinocytosis were involved in the internalization of CHSP NPs. The intracellular trafficking study demonstrated that CHSP NPs were entrapped in the lysosomes at 1 hour after incubation; colocalization of NPs with either the Golgi apparatus or the endoplasmic reticula was not observed during the entire course of the study. These results suggested that the CHSP NPs may serve as a versatile carrier for intracellular delivery of therapeutic agents.