Statistical analysis
Differences were evaluated for significance (* p ≤ 0.05; ** p ≤ 0.01, *** p ≤ 0.001) by using the non-parametric one-tailed Mann-Whitney-test (Prism version 7 for Windows; GraphPad, La Jolla, CA, USA) and a two tailed Student t-test was used (Prism version 7 for Windows; GraphPad, La Jolla, CA, USA). Data are shown as mean values + s.e.m. For correlation of two parameters GraphPad Prism software (version 7 for Windows) was used.