Polyphenol-rich propolis extracts from China and Brazil exert anti-inflammatory effects by modulating ubiquitination of TRAF6 during the activation of NF-κB

Abstract

Propolis has documented anti-inflammatory properties, although its mechanisms of action are poorly understood. In this study, the anti-inflammatory effects of polyphenol-rich propolis extracts (PPE) from China (CPPE) and Brazil (BPPE) were examined. Oral administration of PPE to lipopolysaccharide (LPS)-challenged mice decreased serum proinflammatory cytokine concentrations and inhibited pulmonary nuclear factor (NF)-κB activation. Both PPE types modulated LPS-induced key inflammatory mediators production in RAW 264.7 macrophages. They also suppressed NF-κB activation in HEK 293T cells, correlating well with their inhibitory effects on IκB phosphorylation and p65 nuclear translocation in LPS-activated macrophages. We found PPE suppressed NF-κB activation through delaying the ubiquitination of TRAF6 in HeLa-T6RZC stable cells and by directly disrupting the polyubiquitin synthesis in an in vitro kinase assay system. Overall, analysis showed substantial compositional differences between CPPE and BPPE; nevertheless, they both displayed similar anti-inflammatory properties through NF-κB-responsive inflammatory gene expressions by inhibiting TRAF6 dependent canonical NF-κB pathway.

Keywords

• Propolis
• Polyphenols
• Anti-inflammatory
• LPS
• TRAF6
• NF-κB