LAUSR

Abstract Mechlorethamine (HN2) is an alkylating agent and sulfur mustard mimetic. Topical exposure to HN2 is associated with tissue blistering. Previous work in our laboratory has shown that ebselen (EB-1) possesses anti-vesicant, anti-inflammatory, anti-bacterial, anti-fungal, and cytoprotective properties, both in vivo and in vitro. We recently reported that ebselen oxide (EB-2), an analog of EB-1 with a tetravalent selenium atom, also possesses anti-bacterial and anti-fungal activity and confers cytoprotection against HN2 in vitro. The purpose of the present study was to determine the vesicant countermeasure potential of EB-2 using the mouse ear vesicant model (MEVM). Compared to control ears, mouse ears exposed to a single dose of HN2 (0.500 µmol/ear) showed an increase in wet weights, ear thickness, hyperplasia, vesication, and inflammatory cell infiltration after 24 h. Fluorescence microscopy of terminal deoxynucleotidyl transferase (TdT) dUTP nick end labeling (TUNEL)-stained sections showed that the occurrence of apoptosis extended from the epidermis of the HN2-treated side, all the way to the contralateral epidermis. In contrast, HN2-exposed ears treated topically with EB-2 at a test dose of 0.250 mg/ear showed a significant decrease in wet weight (12% less vs. HN2 alone), morphometric thickness (13% less vs. HN2 alone), and vesication. In addition, TUNEL staining revealed that HN2 ears treated with EB-2 (0.250 mg/ear) showed a decrease in apoptosis as compared to the HN2 group. EB-2 also reduced the abundance of matrix metalloproteinase-9 (MMP-9) in ear tissues exposed to HN2. Taken together, our study demonstrates that EB-2 is an efficacious countermeasure to HN2.