The aqueous extracts of Ageratum conyzoides inhibit inflammation by suppressing NLRP3 inflammasome activation

Abstract

Ethnopharmacological relevance: Ageratum conyzoides L. (Asteraceae), a well-known and widely distributed traditional tropical medicinal herb, has been used to treat diverse diseases. Our preliminary research has shown that aqueous extracts of A. conyzoides leaf (EAC) have anti-inflammatory activity. However, the detailed underlying anti-inflammatory mechanism of EAC is still unclear.

Aim of the study: To determine the anti-inflammatory mechanism of action of EAC.

Materials and methods: The major constituents of EAC were identified by ultra-performance liquid chromatography (UPLC) combined with quadrupole-time-of-flight mass/mass spectrometry (UPLC-Q-TOF-MS/MS). LPS and ATP were used to activate the NLRP3 inflammasome in two types of macrophages (RAW 264.7 and THP-1 cells). The cytotoxicity of EAC was measured by the CCK8 assay. The levels of inflammatory cytokines and NLRP3 inflammasome-related proteins were detected by ELISA and western blotting (WB), respectively. The oligomerization of NLRP3 and ASC and the resulting inflammasome complex formation were observed by immunofluorescence. The intracellular reactive oxygen species (ROS) level was measured by flow cytometry. Finally, an MSU-induced peritonitis model was established to evaluate the anti-inflammatory effects of EAC in vivo.

Results: Twenty constituents were identified in the EAC. Kaempferol 3,7-diglucoside, 1,3,5-tricaffeoylquinic acid, and kaempferol 3,7,4'-triglucoside were found to be the most potent ingredients. EAC significantly reduced the levels of IL-1β, IL-18, TNF-α, and caspase-1 in the two types of activated macrophages, implying that EAC can inhibit the activation of the NLRP3 inflammasome. A mechanistic study revealed that EAC inhibited NLRP3 inflammasome activation by blocking NF-κB signalling pathway activation and scavenging the level of intracellular ROS to prevent NLRP3 inflammasome assembly in macrophages. Furthermore, EAC attenuated the in vivo expression of inflammatory cytokines by suppressing NLRP3 inflammasome activation in a peritonitis mouse model.

Conclusion: Our results demonstrated that EAC inhibited inflammation by suppressing NLRP3 inflammasome activation, highlighting that this traditional herbal medicine might be used to treat NLRP3 inflammasome-driven inflammatory diseases.

Keywords: Ageratum conyzoides; Anti-inflammatory activity; EAC; NLRP3 inflammasome.