[Inhibition of angiogenesis in the cornea with amiloride]

For its transparency, avascularity and possibility of measurement of the new vessels ingrowth, cornea is a frequent model for angiogenesis research. New vessels are made in several phases: after the action of the stimulus, there is a localised fragmentation of the basal membrane and the extracellular matrix around the involved capillary. Then, endothelial cells migrate through the openings in the capillary wall and the lysis of the extracellular matrix continues as a new vessel is being formed. Enzymes, plasminogen-activators, convert plasminogen from the blood and tissues to plasmin which starts proteolytic cascade of the lysis of the extracellular matrix. Amilorid, previously known as a diuretic, is found to be a competitive inhibitor of plasminogen activator-urokinase (u-PA). Its effect was shown in the prostaglandin-induced model of corneal vascularization [6].

The purpose of this work is to show that amilorid acts as an angiostatic in the traumatic model of corneal vascularization.

There were two groups of experimental animals (rabbits, weight 1.5-3 kg). Deepitelisation and trephination were performed on all corneas (traumatic model of vascularisation). The first group of animals (17 eyes) was given 15 mg of amilorid (Sigma) intraperitoneally for five days, while the control group consisted of 7 eyes. Neovascularization was measured after 5 and 15 days. Animals were sacrificed on day 15. Three eyes from each group were tested for corneal wound tensile strength.

In the experimental group there was a 0.5 mm ingrowth of the new vessels after the first five days and no further ingrowth till the end of the experiment. In the control group there was a 2 mm ingrowth after five days, and a further 1 mm after the next ten days. No statistical difference was found with regard to tensile strengths of the corneal wounds between the two groups.

Although the traumatic model is closer to the clinical situation than the prostaglandin-induced vascularization model, more potential angiogenic factors are involved. Trephination damages basal membrane which may liberate angiogenic substances (heparan-sulphate, for example) [9]. Products of damaged cells attract leucocytes by haemotaxis. Also, hyopxia in the depth of the wound may be the site of macrophage induced angiogenesis [10]. It is difficult to say at which point amilorid acts but, considering the new vessel ingrowth for only 0.5 mm, it might be at the beginning of the process (lysis of extracellular matrix).

Amilorid acts as angiogenesis inhibitor in the traumatic corneal vascularization model without changing the tensile strength of the wound.