Evaluation of barrier creams against sulphur mustard: (II) In vivo and in vitro studies using the domestic white pig.

Previous studies in our laboratory have demonstrated that barrier creams, comprising perfluorinated polymers, are effective against the chemical warfare agent sulphur mustard (SM) when evaluated using human skin in vitro. The purpose of this follow-up study was to further evaluate three candidate (perfluorinated) barrier creams against SM (vapour) using the domestic white pig. The severity and progression of the resulting skin lesions were quantified daily for three weeks post-exposure using biophysical measurements of transepidermal water loss (TEWL) and skin reflectance spectroscopy (SRS). Skin biopsies obtained post-mortem were evaluated by light microscopy and additional skin samples were obtained from adjacent (unexposed) skin sites for a comparative in vitro skin absorption study. Samples of SM vapour within the dosing chambers were measured ex vivo to ascertain the exposure dose (Ct). The three creams were highly effective against SM in vivo (Ct approximately 5000 mg.min.m(-3)): After 3 weeks, barrier cream pre-treated sites were not significantly different from control (unexposed) skin when evaluated by TEWL, SRS or histology. In contrast, skin exposed to SM without pre-treatment showed evidence of persistent damage that was consistent with the slow healing time observed in humans. The amount of SM absorbed in vitro in untreated pig skin was similar to that required to cause comparable lesions in human skin (8-20 and 4-10 microg.cm(-2), respectively), further validating the use of pigs as a toxicologically-relevant dermal model for SM exposure.

Examination of changes in connective tissue macromolecular components of large white pig skin following application of Lewisite vapour.

The aim of this study was to provide information about the degradative processes that occur in major connective tissue components in skin following exposure of large white pigs to Lewisite vapour. Of particular interest were alterations in glycoproteins, which are known to mediate dermo-epidermal attachment (laminin and type IV collagen) and the main collagen found in the dermis (type III collagen). The immunostaining of transfer blots from skin extracts run on sodium dodecyl sulphate polyacrylamide gel electrophoresis gels revealed no evidence of cross-linking of laminin or of type III or IV collagen. However, there was evidence of a very considerable degradation of laminin and, to a lesser extent, of type IV collagen. Type III collagen did not appear to be degraded in skin exposed to Lewisite. These degradative processes appeared to be more severe than found in previous studies in Yucatan mini-pigs percutaneously exposed to sulphur mustard, in which only laminin was found to undergo partial cleavage rather than wholesale degradation. The results suggest that damage to macromolecular components in the sub-epidermal basement membrane in skin which mediate dermo-epidermal separation processes may be a common feature in the mechanism of action of vesicating agents such as Lewisite and sulphur mustard. It is of interest that the damage to laminin in this study appeared to be more severe than that previously found for sulphur mustard. This suggests that skin can suffer substantial damage yet, in the case of Lewisite exposure, recover relatively quickly. However, Lewisite is not an alkylating agent. Sulphur mustard, in contrast, generates characteristically slow healing lesions, most probably because of its ability to alkylate cell types that normally would be involved in skin regenerative processes.