Data analysis
Data processing and displaying were performed using GraphPad Prism 5 (GraphPad Software, USA). Mean and standard deviation were displayed for all data sets. Statistical significance was determined using either Student’s t -test or two-way ANOVA followed by Tukey’s post hoc test (p < 0.05). Groups with significant differences are shown with alphabetic letters to signify ranking of means. Groups indicated with the same letters were not found to be significantly different.