2.1 Preparation of HPMEC
HPMEC was purchased from Guangzhou Dewei Biological Technology Co. Ltd, China. HPMEC was cultured in the endothelial cell medium with 10% fetal bovine serum (ScienCell, America) at 37 °C in a humidified incubator with 5% CO2. All experiments were carried out during the logarithmic phase of cell growth. The account of cells was adjusted to 1x106 /ml by serum-free medium before culture, inoculating into six-well plates, and incubated at 5% CO2 and 37 °C.