Effects of inhibition of urokinase-type plasminogen activator (u-PA) by amiloride in the cornea and tear fluid of eyes irradiated with UVB

The purpose of the present study was to test our hypothesis that amiloride, a specific u-PA inhibitor, effectively decreases u-PA activity in cornea as well as in tear fluid and favourably affects corneal healing. Therefore, comparative histochemical and biochemical studies of u-PA and the effects of amiloride were performed on rabbit corneas and tear fluid using the sensitive fluorogenic substrate Z-Gly-Gly-Arg-7-amino-4-trifluoromethylcoumarin. Rabbit eyes were repeatedly irradiated with UVB for 9 days and during the irradiation topically treated with amiloride (1 mg/ml saline) or placebo (saline) (dropwise, 5 times daily). Results show that in placebo-treated eyes, UVB evoked the appearance of u-PA activity in cornea and tear fluid in early stages of irradiation, and u-PA levels increased during irradiation. Corneal epithelium was gradually lost and remnants of the epithelium as well as keratocytes in the upper part of corneal stroma showed high u-PA activity. Finally, corneas lost their epithelium completely. In corneal stroma, numerous u-PA-containing inflammatory cells were present. Corneas were vascularized. When amiloride was dropped on the eye surface on the first day of irradiation and subsequently daily until the end of the experiment, u-PA activity in both cornea and tear fluid was strongly inhibited. Corneas were covered with a continuous epithelium until the end of the experiment. The number of inflammatory cells was significantly decreased. Corneal vascularization was reduced by 50%. In conclusion, early application of amiloride inhibited u-PA activity in UVB-irradiated corneas as well as in tear fluid and diminished the development of corneal pathology.