Assessment of cutaneous sulfur mustard injury in the weanling pig

Background/aims: The euthymic hairless guinea pig was the animal model of choice at this laboratory for vesicant injury research. The supply of these animals, however, was interrupted in 1993 by an outbreak of Lisferia monocyfogenes at the commercial supplier's breeding facility, thereby forcing a search for alternative animal models. This report describes the development of a weanling pig model for use in evaluating the severity of skin lesions induced by sulfur mustard [bis(2-chloroethyl)sulfide; SM] using a variety of bioengineering techniques. These methods include reflectance colorimetry (erythema response), high frequency ultrasound imaging (edema response) and a modified dermal torque meter procedure to test for Nikolsky's sign (damage at the dermal-epidermal junction). The time course and exposure time-dependence of SM-induced lesions for these parameters were characterized in this model and compared with previous results in the haired and hairless guinea pig. Methods: Six male Yorkshire Cross pigs (7–10 kg) were used in this study. The hair on the dorsal surface of each animal was shaved the afternoon prior to SM exposure. Twenty-four dorsal skin sites on each pig were exposed to saturated SM vapor (1.4 mg/l) using 14-mm diameter vapor cups for 0 (control), 5, 10, 15, 20, or 25 min, with four sites per exposure level. Control and exposure sites were rotated to prevent site-specific biases. Lesions were evaluated for erythema (reflectance colorimeter) at 4, 6, 12, 24 and 48 h post-exposure, and for edema (high frequency ultrasound) at 6, 12, 24, and 48 h post-exposure. Evaluations for Nikolsky's sign and histopathology were conducted at 48 h post-exposure. Results: Maximum erythema responses occurred at 24 h postexposure for all SM exposure times (5, 10, 15, 20 and 25 min). The overall maximum response occurred with a 15-min SM vapor exposure at 24 h post-exposure. Exposures longer than 15 min did not induce significantly greater erythema at any of the time points examined. The earliest time point at which significant edema was noted was at 12 h for the 15- and 25-min SM vapor groups. Maximum edema occurred at 48 h following a 15-min exposure. No significant increase in edema was noted at any observation time point with exposures longer than 15 min. All sites showed a weakening of the dermal-epidermal junction (positive Nikolsky's sign) 48 h after a 15-min or longer SM vapor challenge. The histologic severity of the lesions did not significantly worsen as the vapor exposure was increased beyond 15 min. (Following a 15-min SM exposure, incidences of epidermal necrosis, pustular epidermitis, microblisters and vascular damage had reached 100%, with maximum mean severity scores.) The weanling pig is more resistant to the effects of SM vapor than either the haired or hairless guinea pig, showing a delayed response and requiring a longer exposure time to generate the same (quantitative and qualitative) response in erythema, Nikolsky's sign and microblister formation. SM vapor-induced edema formation in the weanling pig is not as severe as in the guinea pig models. Conclusions: Erythema, Nikolsky's sign and microblisters all appear to be excellent parameters for evaluating SM vapor-induced cutaneous damage in the weanling pig. Even though the exposure time-dependent response of cutaneous exposure to SM vapor in humans more closely parallels those of the haired and hairless guinea pig with respect to dermal-epidermal separation, weanling pig skin shares many more similarities to human skin and has the potential to be a useful model for antivesicant research. This model should prove valuable in 1) efficacy testing of pretreatments, treatments and topical skin protectants; 2) wound healing studies; 3) evaluationlof skinlwound decontamination systems; and 4) basic vesicant research.