Inhibition of endotoxin induced uveitis and potentiation of cyclooxygenase–2 protein expression by alpha–melanocyte–stimulating hormone

Abstract

Abstract: : Purpose:We investigated the efficacy of alpha–melanocyte–stimulating hormone (alpha–MSH) on endotoxin–induced uveitis (EIU) in rats. Several previous studies have demonstrated that there are various inflammatory reactions mediated by an alpha–MSH receptor in macrophages. In addition, as it is known cyclooxygenase (COX)–2 is induced by a variety of stimuli and plays an important role in inflammation, we also investigated the COX–2 expression in macrophage cells treated with alpha–MSH in vitro to clarify its anti–inflammatory effect. Methods:EIU was induced in male Lewis rats by a footpad injection of lipopolysaccharide (LPS). The number of infiltrating cells and protein concentration in the aqueous humor collected 24 hours after the LPS treatment was determined. The levels of prostaglandin (PG)–E2, tumor necrosis factor (TNF)–alpha, interleukin (IL)–6, monocyte chemoattractant protein (MCP)–1 production and IL–12 were determined. RAW 264.7 cells were pretreated with various concentrations of alpha–MSH for 24 hours and subsequently incubated with 10 µg /ml of lipopolysaccharide for 24 hours. COX–2 protein expression was analyzed by western blotting method. Results: Alpha–MSH suppressed the development of EIU in a dose–dependent fashion. The treatment with alpha–MSH reduced the PGE2, TNF–alpha, IL–6, MCP–1 and IL–12 concentrations in aqueous humor. The COX–2 protein expression in the alpha–MSH group decreased. Conclusions: This study suggests that alpha–MSH has an anti–ocular inflammatory effect, via the suppression of PGE2, TNF–alpha, IL–6, MCP–1 and IL–12 production and blocking of COX–2 expression.

Keywords: melanocytes • uvea • cytokines/chemokines