PAF antagonists as possible inhibitors of corneal epithelial defects and ulceration.

The extracellular matrix (ECM) plays a crucial role in cell adhesion, differentiation and wound-healing. Its stability is tightly controlled by enzymes that regulate the metabolism of its components (e.g collagen, fibronectin, laminin). We have found that in the cornea, a potent lipid inflammatory mediator platelet-activating factor (PAF) activates the expression of two metalloproteinases (MMP-1 and MMP-9) as well as urokinase-plasminogen activator (uPA). uPA is of particular interest because, as a serine protease, it is at the top of the protease cascade. PAF may contribute to the destruction of the ECM and the formation of epithelial defects and corneal ulcers by activating uPA and then proteases. We also investigated how several PAF antagonists with different binding affinities can block the expression of the uPA gene. Our results suggest that PAF antagonists with affinities for intracellular binding sites and/or specific structures derived from triazolobenzodiazepine could be of therapeutic use to limit the breakdown of the ECM and the development of ulcer formation.