Inhibition of collagenase breakdown of equine corneas by tetanus antitoxin, equine serum and acetylcysteine.
OBJECTIVE
To determine whether tetanus antitoxin, equine serum, and acetylcysteine, which are currently used in the treatment of equine corneal ulcer, inhibit the digestion of equine corneal collagen when exposed to collagenase in vitro.


METHODS
Corneas from 40 adult horses.


METHODS
Sections of equine corneas were incubated with saline, a solution of bacterial collagenase in saline, bacterial collagenase in saline plus equine tetanus antitoxin, bacterial collagenase in saline plus equine serum, or bacterial collagenase in saline plus acetylcysteine. Each one of the collagenase inhibitors was tested at different concentrations. The degree of corneal collagen digestion was determined by concentrations of hydroxyproline released into the incubation media and/or by weight loss of the cornea.


RESULTS
Corneas exposed to collagenase released a significant (0.05 level) large amount of hydroxyproline (43.1 +/- 2.3 microg/mL/100 mg cornea/5 h) and decreased cornea weight by up to 89%. Blood serum (200 microL/mL), purified albumin or globulin fractions of serum, tetanus antitoxin (120 units/mL), and acetylcysteine (20 mg/mL) when used at the highest concentrations blocked collagenase digestive activity by approximately 50%. Dilution of inhibitors decreased corneal protection and linearly increased corneal weight loss. Purified equine serum albumin and globulin fractions were equally effective in protecting corneas.


CONCLUSIONS
This experiment indicates that tetanus antitoxin, serum and acetylcysteine equally protected corneas from collagenase digestion, in vitro. However, a clinical trial is needed to establish relative therapeutic value.
Haffner
John C
JC
Department of Large Animal Clinical Sciences, College of Veterinary Medicine, The University of Tennessee, 2407 River Drive, Knoxville, TN 37996-4543, USA.
Fecteau
Kellie A
KA
Eiler
Hugo
H
D000111:Acetylcysteine / Q000494:pharmacology*; D000818:Animals; D001798:Blood Proteins / Q000494:pharmacology*; D003013:Clostridium / Q000201:enzymology; D003315:Cornea / Q000187:drug effects*; D003320:Corneal Ulcer / Q000188:drug therapy / Q000662:veterinary; D006734:Horse Diseases / Q000188:drug therapy; D006736:Horses; D003012:Microbial Collagenase / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D013743:Tetanus Antitoxin / Q000494:pharmacology*
D001798:Blood Proteins; D013743:Tetanus Antitoxin; D003012:Microbial Collagenase; D000111:Acetylcysteine