Figure 4. Analysis of telomerase activity as assayed by the telomeric repeat amplification protocol. A: Telomerase activity was detected in early passage nonsenescent late outgrowth endothelial progenitor cells (OECs) and Human Umbilical Vein Endothelial Cells (HUVEC) cultured in complete angiogenic medium (EGM-2MV). Negative control represents telomerase activity of heat-inactivated OEC samples, positive control corresponds to the tumor cell sample provided by the manufacturer (TeloTAGGG Telomerase PCR ELISA, Roche Applied Science, Indianapolis, IN). NS denotes not statistically significant difference in telomerase activity between HUVEC and OECs. B: Telomerase activity is decreased in OECs treated with 3, 6 and 10 μM SU5416 for 3 days compared to control EGM-2MV (with the addition of 10 μl DMSO/ml, 0 μM SU5416). C: Telomerase activity is decreased in OECs treated with EGM-2MV supplemented with inhibitors SU5416 (6 μM), ZM323881 (10 μM), KRN633 (4 μM), Wortmannin (100 nM), Ly 294002 (5 μM) and Bisindolylmaleimide I (1 μM) for 3 days compraed to control medium (EGM-2MV with the addition of 10 μl DMSO/ml). D: Recovery of telomerase activity is dose-dependent. Telomerase activity was assessed for control OECs at day 0 and 7, OECs inhibited for 7 days with SU5416 3 μM and 6 μM and for OECs returned to EGM-2MV without inhibitor for another 3 days after 7 days of inhibition. Graphs A and C represent the mean±SEM telomerase activity, B and D the mean percentage in telomerase activity as compared to control (medium without inhibitor in B, medium without inhibitor after 10 days of culture in D), for three independent experiments each (OECs derived from three different patients). Student’s t-test for paired data was used for statistical comparison between control and inhibitory conditions. * indicates a statistically significant difference (p<0.05) as compared to control.