Shikonin reduces oedema induced by phorbol ester by interfering with IκBα degradation thus inhibiting translocation of NF-κB to the nucleus

Background and purpose: In the present paper we studied the effect of shikonin on ear oedema induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), and determined the mechanisms through which shikonin might exert its topical anti-inflammatory action. Experimental approach: Acute ear oedema was induced in mice by topical application of TPA. The in vitro assays used macrophages RAW 264.7 cells stimulated with lipopolysaccharide. Cyclooxygenase-2, inducible nitric oxide synthase, protein kinase C alpha, extracellular signal-regulated protein kinase (ERK), phosphorylated ERK (pERK), c-Jun N-terminal kinase (JNK), pJNK, p38, p-p38, p65, p-p65, inhibitor protein of nuclear factor-kappa B (NF-kappa B) (I kappa B alpha) and pI kappa B alpha were measured by Western blotting, activation and binding of NF-kappa B to DNA was detected by reporter gene and electrophoretic mobility shift assay, respectively, and NF-kappa B p65 localization was detected by immunocytochemistry. Key results: Shikonin reduced the oedema (inhibitory dose 50 = 1.0 mg per ear), the expression of cyclooxygenase-2 (70%) and of inducible nitric oxide synthase (100%) in vivo. It significantly decreased TPA-induced translocation of protein kinase C alpha, the phosphorylation and activation of ERK, the nuclear translocation of NF-kappa B and the TPA-induced NF-kappa B-DNA-binding activity in mouse skin. Moreover, in RAW 264.7 cells, shikonin significantly inhibited the binding of NF-kappa B to DNA in a dose-dependent manner and the nuclear translocation of p65. Conclusions and implications: Shikonin exerted its topical anti-inflammatory action by interfering with the degradation of I kappa B alpha, thus inhibiting the activation of NF-kappa B.