Fig. 4

Effect of hyperthermia on endothelial progenitor cell (EPC) vasculogenesis, human umbilical vein endothelial cell (HUVEC) tube formation, and viability. After EPC or HUVECs were plated on Matrigel for 1 h, cells were cultured at 39 °C for 2–18 h; after 2, 4 and 18 h, EPC clusters and HUVEC tube branches were counted in 5/x100 fields, and the percentage of EPC clusters and tube formation (compared to control) was plotted for each time point. a Hyperthermia inhibited HUVEC tube formation and b EPC cluster formation on Matrigel. c-f Representative images of HUVEC capillary networks and EPC cluster formation on Matrigel at different temperatures. c HUVEC network at 37 °C. Exposure to 39 °C for 4 h inhibited HUVEC capillary network formation (d). e EPC cluster formation on Matrigel at 37 °C was also reduced by incubation at 39 °C for 4 h (f). g Effect of hyperthermia on cell viability. Cell viability was measured by XTT assay 2-18 h after heating. Cell viability of untreated cells is assumed as 100 %. Incubation at 39 °C at 2, 4 and 18 h did not cause cell death. All data represent the mean ± SD of three experiments. Statistical differences between heat treatment and control were determined by two-way analysis of variance (ANOVA), followed by paired two-tailed T-test. ∗ = P < 0.05; ** = P < 0.01. XTT xylin tetrazolium