Molecular mechanism underlying anti-inflammatory activities of lirioresinol B dimethyl ether through suppression of NF-κB and MAPK signaling in in vitro and in vivo models

Abstract

The aim of the present study is to explore the anti-inflammatory mechanism of lirioresinol B dimethyl ether via inhibition of multiple signaling pathways in both in vitro and in vivo pharmacological models. To determine the anti-inflammatory activity of the lirioresinol B dimethyl ether, RAW 264.7 macrophages challenged with lipopolysaccharide (LPS) were treated with various concentrations of lirioresinol B dimethyl ether (5, 15, 25, and 50 μM). The results indicated that pretreatment with lirioresinol B dimethyl ether significantly suppressed nuclear factor kappa B (NF-κB) activation, nitric oxide (NO) production, the protein expressions of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Lirioresinol B dimethyl ether inhibited LPS-induced activation of production of pro-inflammatory cytokines as well as prostaglandin E₂ (PGE₂) release. The results obtained by electrophoretic mobility shift assay (EMSA) demonstrated a concentration dependent reduction of the LPS-stimulated activation of NF-κB and activator protein-1 (AP-1) by lirioresinol B dimethyl ether in in vitro and in vivo models. Moreover, lirioresinol B dimethyl ether also reduced the expression of toll-like receptor (TLR)-4 protein and myeloid differentiation primary response gene 88 (MyD88) as well as promoted the degradation of IκBα. Lirioresinol B dimethyl ether also significantly down-regulated the phosphorylation of Jun N-terminal kinase (JNK), p-38 and extracellular signal-regulated kinase (ERK). Furthermore, the results of acute and chronic inflammation demonstrated that lirioresinol B dimethyl ether (10 and 50 mg per kg) reduced paw edema and mechanical hyperalgesia in carrageenan- and Complete Freund's Adjuvant (CFA)-induced in vivo mouse models, respectively. Hence, the current results indicate that lirioresinol B dimethyl ether either act by inhibiting pro-inflammatory mediators through down-regulation of mitogen activated protein kinases (MAPKs) signaling pathways and reduction of NF-κB activation.

Keywords: Anti-inflammatory; Carrageenan; Lirioresinol B dimethyl ether; MAPKs/AP-1; NF-κB.