Effect of TFPIc23 on endothelial spheroid vessel outgrowth. (A) Endothelial cell spheroids were suspended in collagen, and bFGF was added to induce vessel outgrowth. Increasing amounts of TFPIc23 were added with the bFGF, and vessel growth was assessed 24 hours later. Control spheroids and spheroids grown in the presence of 5 μM, 20 μM, and 50 μM TFPIc23 are shown in the top panels. The bottom panels show the effect of VLDL receptor antibody assessed by preincubating spheroids with R4522 and then treating with TFPIc23. Control spheroids were treated with bFGF and R4522 and bFGF alone. Original magnification × 100. (B) Quantification of spheroid tubule outgrowth. The effects of increasing amounts of TFPIc23 in the presence or absence of the VLDL receptor antibody R4522 were quantified by measuring the total length of all vessels from each spheroid (2-8 spheroids/well).