Recombinant kringle 1-3 of plasminogen inhibits rabbit corneal angiogenesis induced by angiogenin

Purpose. Angiostatin is a potent angiogenesis inhibitor that has been identified as a cryptic fragment of plasminogen molecule containing the first four kringle domain. Angiogenin, a 14-kDa monomeric protein, a potent blood vessel inducer, is expressed in tumors and present in mammalian plasma. The purpose of this study was to determine whether recombinant kringle 1-3 (rK1-3) of human plasminogen could interfere with angiogenesis induced by angiogenin and to evaluate the role of angiogenin in corneal angiogenesis in rabbit. Methods. A Hydron polymer pellet containing 2.0 mu g of angiogenin was implanted intrastromally into the superior cornea of each of 44 rabbit eyes. All eyes received an intrastromal pellet and were randomized into either one group treated with 12.5 mu g of rK1-3 (n = 25) or the other group treated with phosphate-buffered saline (PBS; n = 19). Both pellets were positioned in parallel at the site 1.2 mm from the superior limbus. Two masked observers kept the angiogenesis score daily, based on the number and the length of new vessels. The corneas with induced angiogenesis also were examined histologically. Results. On the third day of the angiogenin pellets implantation, the eye treated with rK1-3 had less angiogenesis (mean score, 4.2 +/- 6.6) than eye treated with PBS (mean score, 16.1 +/- 17.1; p < 0.05. Mann-Whitney U test). The cornea treated with PBS also showed much more leukocyte adhesion than the cornea treated with rK1-3. Conclusion. Recombinant kringle 1-3 appears to inhibit angiogenin-induced angiogenesis in a rabbit corneal pocket assay. Recombinant kringle 1-3 may have therapeutic potential as an antiangiogenic agent.