Objective—To examine in vitro effects of various
antiproteolytic compounds on activity of matrix metalloproteinase
(MMP)-2 and -9 in the tear film of horses
with active corneal ulcers.
Sample Population—Samples of tear film obtained
from the eyes of 34 horses with active ulcerative keratitis.
Procedure—Horses were sedated, and tear samples
were collected from the lower fornix of 34 ulcerated
eyes by use of capillary tubes. The protease inhibitors
0.2% EDTA, 0.1% doxycycline, 10% N-acetylcysteine
(NAC), 0.1% solution of a modified dipeptide that contains
hydroxamic acid (ie, ilomostat), 0.1% α1-proteinase
inhibitor (PI), 0.5% α1-PI, and 100% fresh
equine serum (ES) were used to treat pooled samples.
Amount of latent and active MMP-2 and -9 was
measured by optical density scanning of gelatin
zymograms of treated and untreated tear samples.
Results—Pooled tear samples obtained from ulcerated
eyes contained the latent and active forms of
MMP-2 and -9. Compared with MMP activity in
untreated samples, total MMP activity (sum of all
bands detected) observed on the gelatin zymogram
gels was reduced by 99.4% by EDTA, 96.3% by doxycycline,
98.8% by NAC, 98.9% by ilomostat, 52.4%
by 0.1% α1-PI, 93.6% by 0.5% α1-PI, and 90.0% by
Conclusions and Clinical Relevance—We documented
that EDTA, doxycycline, NAC, ilomostat, α1-
PI, and ES inhibited MMP activity in vitro. Because
these compounds use different mechanisms to inhibit
various families of proteases in the tear film of horses,
a combination of these protease inhibitors may be
beneficial for treatment of corneal ulcers in horses.
(Am J Vet Res 2003;64:1081–1087)