Non-parametric data are expressed as median with range of values in parentheses. All statistics were calculated using GraphPad PrismTM version 3.0 for Windows (GraphPad Software, San Diego, California, United States). Non-parametric tests were applied throughout, with differences being considered significant for p values < 0.05. The Mann–Whitney test was used for comparison of two groups, whilst for analysis of three groups the Kruskal–Wallis test with Dunn's multiple comparison test was used.