Shikonin derivatives inhibited LPS-induced NOS in RAW 264.7 cells via downregulation of MAPK/NF-κB signaling

Aim of the study: Shikonin/alkannin (SA) derivatives, analogs of naphthoquinone pigments, are the major components of root extracts of the Chinese medicinal herb (Lithospermum erythrorhizon; LE) and widely distributed in several folk medicines. In the present study, the effect and the underline molecular mechanism of shikonin derivatives isolated from root extracts of Lithospermum euchroma on lipopolysaccharide (LPS)-induced inflammatory response were investigated. Materials and methods: Effects of five SA derivatives, including SA, acetylshikonin, beta,beta-dimethylacrylshikonin, 5,8-dihydroxy-1,4-naphthoquinone, and 1,4-naphthoquinone on LPS-induced nitric oxide (NO) and prostaglandin E2 (PGE2) production in mouse macrophage RAW264.7 cells were examined. Results: Data suggested that SA derivatives inhibited LPS-induced NO and PGE2 production. and iNOS protein expression. RT-PCR analysis showed that SA derivatives diminished LPS-induced iNOS mRNA expression. Moreover, the phosphorylation of extracellular signal-regulated kinase (ERK)1/2 in LPS-stimulated RAW 264.7 cells was concentration-dependently suppressed by SA derivatives. SA inhibited NF-kappa B activation by prevention of the degradation of inhibitory factor-kappa B and p65 level in nuclear fractions induced by LPS. Conclusions: Taken together, these results suggest that the anti-inflammatory properties of SA derivatives might result from inhibition of iNOS protein expression through the downregulation of NF-kappa B activation via suppression of phosphorylation of ERK, in LPS-stimulated RAW 264.7 cells. (C) 2008 Elsevier Ireland Ltd. All rights reserved.