Resibufogenin, One of Bufadienolides in Toad Venom, Suppresses LPS-induced Inflammation Via Inhibiting NF-κB and AP-1 Pathways

Toad venom is a traditional Chinese medicine that has a long history in treating infectious and inflammatory diseases, such as carbuncle, pharyngitis. As one of the major active components in toad venom, resibufogenin (RBG) possesses a variety of pharmacological activities, including lowering blood pressure, reducing proteinuria and preventing oxidative stress. But only its antitumor activity attracts widespread attention in these years. This study aimed to explore the nonnegligible anti-inflammatory activity of RBG in vivo and in vitro. In endotoxemia mice, a single intraperitoneal administration of RBG significantly lowered serum TNF-α, IL-6 and MCP-1 levels. In LPS-stimulated macrophages, RBG decreased LPS-induced pro-inflammatory mediators' productions (e.g., iNOS, IL-6, TNF-α and MCP-1) through suppressing their transcriptions. Mechanism study showed that RBG hindered IκBα phosphorylation and prevented nuclear translocation of p65, thus inactivating nuclear factor-κB (NF-κB) signaling. Concurrently, RBG also dampened activator protein-1 (AP-1) signaling through inhibiting the phosphorylation levels of c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK). Besides LPS (TLR4 ligand) model, RBG also inhibited Pam3CSK4 (TLR2 ligand)- or poly I:C (TLR3 ligand)-induced inflammatory reactions, suggesting that its target(s) site is(are) not on the cytomembrane. These findings not only support the pharmacological basis for the traditional use of toad venom in inflammatory diseases, but also provide a promising anti-inflammatory candidate.