In Vivo Corneal Injury Models with Lewisite and Sulfur Mustard for the Evaluation of Effective Treatments

Abstract

Purpose : Vesicating agents lewisite (2-chlorovinyldichloroarsine; LEW) and sulfur mustard (2,2’-dichloroethyl sulfide; SM) pose a risk of accidental exposure in addition to their feared use as terrorist weapons. Ocular tissue is the most sensitive organ to vesicant exposure with devastating short- and long-term corneal injuries. The goal of this study was to establish useful clinical, histopathological and molecular endpoints to identify and screen therapies for alleviating cornel injury from vesicant exposure.

Methods : Using an efficient vapor exposure system, LEW (0.2 mg/L) and SM (0.4 mg/L)-induced corneal injury was evaluated in New Zealand white rabbits (n=6/group). The right eye of each anesthetized rabbit was exposed to LEW (2.5 or 7.5 min) or SM (5 or 7 min), and the left eye was exposed to dilution air (control). Clinical observations and scoring were performed at day 1 post-exposure and out to day 28. The corneal sections were hematoxylin and eosin as well as immunohistochemical stained and evaluated for LEW- and SM-induced histopathological and molecular alterations.

Results : Corneal opacity was maximal between day 3 and 7 days post-exposure while corneal neovascularization was observed starting 7-14 days post-exposure in both LEW and SM exposed corneas. Histopathological examination showed that both agent exposures for longer durations resulted in optimal injury at day 7 post-exposure. At this time point, significant (p<0.05) increase of 55% and 37% in epithelial degradation and 87% and 79% decrease in stromal keratocytes with longer LEW and SM exposure durations, respectively, was observed. LEW and SM exposures also caused significant (p<0.05) increases in the expression levels of cyclooxygenase-2 (COX-2), vascular endothelial growth factor (VEGF) and metalloproteinase-9 (MMP-9) with optimal effect at day 7 or 14 post-exposure. There was a 3.0-fold and 2.5-fold increase in COX-2 expression, 3.5-fold and 3.6-fold increase in VEGF expression and 3.0-fold and 2.4-fold increase in MMP-9 expression following longer LEW and SM exposure durations, respectively, at optimal injury time point.

Conclusions : The outcomes provide valuable LEW- and SM-induced corneal injury endpoints in a relevant rabbit corneal injury models. We anticipate additional studies to delineate pathways involved in corneal injury and wound healing from LEW and SM exposure and identify effective targeted therapies.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.