Acute-phase effects of single-time topical or systemic corticosteroid application immediately after hot water-induced burn injury of various grades

The aim of this study is to evaluate the effects of corticosteroid application on each grade of burn, and to clarify the underlying mechanisms of the effects, especially in its acute inflammatory phase. To generate three-graded burn models (epidermal burn, or EB; dermal burn, or DB; and subcutaneous burn, or SB), hot water was applied on the back skin of Hos:HR-1 mice. Strongest-class (or high-potent) corticosteroid ointment (DD group) or petrolatum (control group) was applied on the back immediately after the hot water application on mice. Prednisolone sodium succinate (PDN group), 1 mg/kg was orally applied immediately after the hot water application on mice. The mice were sacrificed 1–3 days after hot water application, and the lesional skin samples were provided for histological assessment to enumerate the number of infiltrating inflammatory cells. The mRNA expression levels of inflammatory cytokines (IL-1b, TNFa, IL-6 and IFNg) in the lesional skin were also investigated. As a result, corticosteroid application suppressed the number of infiltrating inflammatory cells in the DD group of EB and SB at the early phase, and in DB at all time-points. However, the number of infiltrating inflammatory cells increased in EB on day 3. Expression of cytokines was generally suppressed in the PDN group of SB. In the cases of EB and DB, some cytokines had decreased but many of the others showed increased expression. In conclusion, the anti-inflammatory effects of corticosteroids are not simple inhibitory effects on inflammatory cell infiltration and cytokine production, but exert more complicated effects in vivo.