Phosgene Oxime Dermal Exposure Induces Inflammation, Mast Cell Activation and Oxidative stress

Abstract

Phosgene Oxime (dichloroform oxime; CX), an urticant classified as a vesicating agent, is a potential chemical threat agent. With faster cutaneous penetration, corrosive properties, and more potent toxicity compared to other vesicating agents, CX causes immediate painful dermal and systemic injuries. However, CX toxicity and its mechanism of action is not well studied. To explore the underlying mechanism of CX-induced dermal toxicity, we exposed the dorsal skin of SKH-1 hairless mice to CX vapor for 0.5 or 1.0 min using two 12 mm vapor caps. Our clinical findings showed that CX exposure causes acute skin lesions such as edema, erythema, necrosis, urticaria and blanching. It also caused decreased heart and respiratory rate, decreased body temperature, and mortality. Skin histopathological analysis showed CX-induced increase in the epidermal, and dermal plus hypodermal thickness, increased polymorphonuclear infiltrates indicating inflammation, and apoptotic cell death. Hyperkeratosis, scab formation was observed only in the skin of male mice at 14 day post-0.5 min CX exposure. CX toxicity symptoms resemble allergic reaction or urticaria, which is reported to be mediated mainly by the activation of mast cells and release of inflammatory mediators. Chemical exposures causing urticaria can lead to oxidative stress or mast cell activation can generate intracellular reactive oxygen species(ROS) to cause oxidative stress. CX cutaneous exposures (0.5 and 1 min) resulted in DNA damage (H2A.X & p53 phosphorylation) and oxidative DNA damage (8-oxo-2-deoxyguanosine expression) as well as lipid peroxidation (4-hydroxynonenal adduct formation). CX exposure also induced inflammatory response evident by neutrophil infiltration (increased myeloperoxidase expression), increased macrophages, and mast cell degranulation that was associated with increased histamine and tryptase levels. In addition, CX exposure also enhanced the expression inflammatory markers COX2 and matrix metallopeptidase 9 within 30 min of its exposure. In male mice, these markers were upregulated till 14 days post-exposure. CX exposure caused increases in a number of skin pro-inflammatory cytokines and chemokines including IL1□, IL6, vascular endothelial growth factor, and CXCL1. CX exposure also decreased the expression of anti-inflammatory cytokines like IL4 and IL10. Further molecular analysis is underway to determine if the signaling pathways related to oxidative stress and mast cell activation could be important contributors in the CX-induced dermal inflammation and toxicity.