TUNEL assay apoptosis of HUVEC. First row: positive control experiment, second row: untreated control experiment, third row: HUVEC treated with EuPO4·H2O at 50 μg/ml for 20 h of incubation at 37°C and fourth row: HUVEC treated with TbPO4·H2O at 50 μg/ml for 24 h of incubation at 37°C. TUNEL assay apoptosis of HUVEC using camptothecin (4 h incubation at 37°C) as positive inducer (First row). A: TMR red -stained nuclei of HUVEc appear in red color due to presence of apoptotic cells, A1: The DAPI-stained nuclei appear in blue and A2: merged picture of A and A1. First Column: The nuclei of HUVEC were stained with TMR red (B-D), red staining was not observed due to absence of no apoptotic cells. Second column: The DAPI-stained nuclei appear in blue (B1-D1), and Third column: merged picture of first and second column (B2-D2).