Vascular endothelial growth factor (VEGF) is a key factor in endothelial cell biol. and blood vessel formation and a candidate therapeutic for the stimulation of angiogenesis-dependent tissue regeneration. The objective of this study was to confer the angiogenic activity of VEGF121 upon the biomaterial fibrin, a natural substrate for endothelial cell growth and clin. accepted as 'fibrin glue'. To achieve this, the authors engineered fibrin-based hydrogels that were covalently modified with VEGF121. Our lab. has recently developed novel methodol. that allows the covalent incorporation of exogenous bioactive peptides by the transglutaminase activity of factor XIIIa into fibrin during coagulation. Here, this ability of factor XIIIa to crosslink addnl. proteins within fibrin was employed to covalently incorporate VEGF121. By recombinant DNA methodol., a mutant VEGF121 variant, a2-PI1-8-VEGF121, which contains an addnl. factor XIIIa substrate sequence NQEQVSPL at the aminoterminus, was expressed in E. coli. In sol. form, the mutant protein fully retained its mitogenic activity for endothelial cells. Using 125I-labeled a2-PI1-8-VEGF121, its covalent incorporation and the efficiency of incorporation into fibrin was demonstrated and characterized. The immobilized, fibrin-conjugated VEGF121 protein remained an active and very efficient mitogen for human endothelial cells grown on two-dimensional VEGF121-modified fibrin surfaces, and the incorporation of increasing amts. of a2-PI1-8-VEGF121 resulted in dose-dependent enhancement of endothelial cell growth. The VEGF-modified fibrin matrixes can be formed as injectable gels in a single-step reaction under physiol. conditions in vivo. When used as a ingrowth matrix, such VEGF incorporating materials could be useful in a variety of clin. situations that require an angiogenic response into an ischemic region or implant. [on SciFinder (R)]