A preliminary study on the interaction between Asn-Gly-Arg (NGR)-modified multifunctional nanoparticles and vascular epithelial cells

Liu, Chunxi; Liu, Tingxian; Yu, Xiaoyue; Gu, Yizhu

The results of the endocytosis kinetic experiments are shown in Fig. 7 . As shown in Fig. 7 , TPIC uptake was enhanced as the incubation time increased at 37 1C, whereas the internalization of TPIC at 4 1C was inhibited, which demonstrated that endocytic uptake of TPIC was an energy-dependent mechanism. Additionally, surface accessible CD13 was also affected by temperature. At 4 1C, there was approximately less than 10% TPIC internalized, resulting in the decrease in surface accessible CD13. At 37 1C, rapid internalization of TPIC was observed and the uptake of TPIC increased with the incubation time. Interestingly, with TPIC uptake increased, the amount of cell surface CD13 appeared to decrease first and then increase. Over the following 1 h, the internalization of TPIC increased rapidly and reached 53% and there was a sharp decline of surface CD13, which reached the lowest value of 66%. This finding implies that CD13 was involved in the endocytosis process of TPIC. After 1 h, the TPIC endocytosis process continued, but the endocytosis speed reduced because of the lower amount of CD13 on the cell surface. With the increase of the extension of time, the cell CD13 could return to the cell surface through the receptor cycle. With the endocytosis process, the amount of CD13 on the surface was dynamically changed. However, at any time point, the recycled CD13 continued to participate in the uptake process of TPIC so that internalized TPIC gradually increased.