Tissue Kallikrein Attenuates Choroidal Neovascularization via Cleavage of Vascular Endothelial Growth Factor

PURPOSE: To investigate the antiangiogenic properties of tissue kallikrein in a murine model of laser-induced choroidal neovascularization (CNV). METHODS: CNV was induced in male C57BL/6J mice by laser photocoagulation. The animals received daily subcutaneous injections of tissue kallikrein (50 μg/kg) or vehicle control for 2 days before the laser photocoagulation, and this treatment continued until sample collection. Seven days after laser injury, the CNV size was quantified. The levels of monocyte chemoattractant protein (MCP)-1, intercellular adhesion molecule (ICAM)-1, and interleukin (IL)-6 were assessed by enzyme-linked immunosorbent assay 3 days after laser injury. Cleavage of mouse VEGF with tissue kallikrein was assessed in vivo and in vitro. The protein levels of bradykinin were assessed in the RPE-choroid complexes and hearts. RESULTS: A significant decrease in CNV size was observed in animals treated with tissue kallikrein (27,168.3 ± 2432.2 μm(2)) compared with vehicle-treated controls (36,374.6 ± 3204.1 μm(2), P < 0.05). Tissue kallikrein treatment significantly reduced MCP-1, ICAM-1, and IL-6 levels in RPE-choroid complexes. Furthermore, immunoblotting showed the bands, presumably corresponding to the fragmented VEGF(164) protein, in the samples of both mouse VEGF preincubated with tissue kallikrein and RPE-choroid complexes obtained from animals treated with tissue kallikrein. In addition, bradykinin was unchanged in the RPE-choroid complexes of animals treated with tissue kallikrein, whereas the level of bradykinin was increased in the heart obtained from these experimental animals. CONCLUSIONS: The current data indicate that kallikrein exhibits antiangiogenic properties by cleaving VEGF(164) in a laser-induced CNV model.