OBJECTIVE To compare the efficacy of various concentrations and combinations of serum,
EDTA, 3
tetracyclines, and
N-acetylcysteine (NAC) for
collagenase inhibition in an in vitro corneal degradation model. SAMPLE Grossly normal corneas from recently euthanized dogs and horses and fresh serum from healthy dogs and horses. PROCEDURES Serum was pooled by species for in vitro use. For each species, sections of cornea were dried, weighed, and incubated with clostridial
collagenase (800 U/mL) in 5 mL of a 5mM
calcium chloride-
saline (0.9% NaCl) incubation
solution and 500 μL of 1 of 19 treatments (homologous serum; 0.3%, 1.0%, or 2%
EDTA; 0.1%, 0.5%, or 1.0%
tetracycline,
doxycycline, or
minocycline; 0.5%, 1.0%, or 5.0% NAC; serum with 0.5%
tetracycline; serum with 1.0%
EDTA; or 1.0%
EDTA with 0.5%
tetracycline). Positive and negative control specimens were incubated with 5 mL of incubation
solution with and without
collagenase, respectively. Each control and treatment was replicated 4 times for each species. Following incubation, corneal specimens were dried and reweighed. The percentage corneal degradation was calculated and compared among treatments within each species. RESULTS Treatments with
tetracyclines at concentrations ≥ 0.5%, with
EDTA at concentrations ≥ 0.3%, and with NAC at concentrations ≥ 0.5% were more effective at preventing corneal degradation than serum in both species. The efficacy of each combination treatment was equal to or less than that of its components. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested
EDTA,
tetracyclines, and NAC may be beneficial for topical treatment of
keratomalacia, but in vivo studies are required.