Andrographolide acts as an anti-inflammatory agent in LPS-stimulated RAW264.7 macrophages by inhibiting STAT3-mediated suppression of the NF-κB pathway

Inflammation is involved in numerous diseases, such as chronic inflammatory disease and cancer. Many plant products exhibit useful biological activities, including antifungal, antibacterial, and anti-inflammatory actions. However, our understanding of the anti-inflammatory effects of andrographolide is limited. We use lipopolysaccharide (LPS)-stimulated macrophages as a model of inflammation to investigate the anti-inflammatory effects of andrographolide, which contains polyphenolic structures. We found that andrographolide exhibited a potent anti-inflammatory effect. In this study, we investigated the inhibitory effects of andrographolide on the induction of nitric oxide synthase (NOS) and cyclooxygenase-2 (COX-2) as well as their respective downstream products, NO and PGE2, in RAW264.7 cells treated with LPS. Treatment with andrographolide also reduced nuclear factor-κB (NF-κB) and activation protein-1 (AP-1) DNA-binding activity. Western blot analysis showed that andrographolide significantly inhibited the phosphorylation of signal transducer and activator of transcription-3 (STAT3) and the protein expression of CCAAT/enhancer-binding protein δ (C/EBPδ). We also found that andrographolide suppressed LPS-induced suppressor of cytokine signalling 1 and 3 (SOCS1 and 3) mRNA expression, which, in turn, inhibited apoptosis signalling and mitochondria membrane potential activation. Our results demonstrate that andrographolide downregulates inflammatory iNOS and COX-2 gene expression by inhibiting the activation of NF-κB and STAT3 by interfering with the expression of SOCS1 and SOCS3 signalling. Therefore, andrographolide exerts a potent anti-inflammatory effect and could potentially be developed as a useful agent for the chemoprevention of cancer or inflammatory diseases.