Thunbergia alata inhibits inflammatory responses through the inactivation of ERK and STAT3 in macrophages

Abstract

Thunbergia alata (Acanthaceae) has been used traditionally to treat various inflammatory diseases such as fever, cough and diarrhea in East African countries including Uganda and Kenya. However, systemic studies elucidating the anti-inflammatory effects and precise mechanisms of action of T. alata have not been conducted, to the best of our knowledge. To address these concerns, we explored the anti-inflammatory effects of a methanol extract of T. alata (MTA) in macrophages. Non-cytotoxic concentrations of MTA (300 g/ml) inhibited nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages by transcriptional regulation of inducible NO synthase in a dose-dependent manner. The expression of cyclooxygenase-2, the enzyme responsible for the production of prostaglandin E-2, was unchanged by MTA at the mRNA and protein levels. MTA treatment inhibited interleukin (IL)-6 inflammatory cytokines, including IL-6 and IL-1. Tumor necrosis factor- production and mRNA expression were not regulated by MTA treatment. The decreased production of inflammatory mediators by MTA was followed by the reduced phosphorylation of extracellular signal-regulated kinase (ERK) and signal transducer and activator of transcription 3 (STAT3). MTA treatment had no effect on activity of other mitogen-activated protein kinases (MAPKs), p38, c-Jun N-terminal kinase (JNK), and nuclear factor-B (NF-B). These results indicate that MTA selectively inhibits the excessive production of inflammatory mediators in LPS-stimulated murine macrophages by reducing the activity of ERK and STAT3, suggesting that MTA plays an important inhibitory role in the modulation of severe inflammation.