The kallikrein system in retinal damage/protection.

Kallikrein is a serine protease involved in the kallikrein-kinnin system. Kallikrein is derived from the blood plasma or tissue, and is correlated with aggravation and improvement in eye diseases, such as, glaucoma, diabetic retinopathy, age-related macular degeneration, and ocular ischemic syndrome. The plasma kallikrein stimulates retinal vascular permeability and intraocular hemorrhage. On the other hand, we had reported that the tissue kallikrein normalizes retinal vasopermeability and inhibited retinal neovascularization and retinal ischemic injury. The protective mechanisms of the tissue-derived kallikrein include the cleavage of vascular endothelial growth factor (VEGF), which suggests that the tissue kallikrein could be potentially-effective against any disease involving the VEGF production.