Statistical analysis
All continuous variables were expressed as the median with an interquartile range(IQR) or mean with standard deviation(SD), as appropriate. All groups were tested for the normal distribution with a Kolmogorov-Smirnov test. For the normally distributed data, a one-way analysis of variance (ANOVA) was used to analyze more than two groups. Data that were not normally distributed were tested by a one-way Kruskal-Wallis test for more than two groups. All statistical analysis was carried out using Graphpad Prism version 5 (GraphPad, La Jolla, CA, USA) and SPSS 22.0 (College Station, TX, USA) software. In the graphs, the p values are indicated as follows: * < 0.05; ** < 0.01; *** < 0.001.