Statistical analysis was performed using SPSS version 16.0 for Windows (SPSS Inc., Chicago, IL, USA) [8 ,6 (link)] and GraphPad Prism 5.0 [9 (link)–11 (link)]. T test and 2-way ANOVA was applied for comparison between 2 or more groups. Chi-square test or Kruskal-Wallis test were also used when appropriate. Statistical significance was reached when the p value was < 0.05.