Anthocyanins from <i>Hibiscus syriacus</i> L. Inhibit NLRP3 Inflammasome in BV2 Microglia Cells by Alleviating NF‐<i>κ</i>B‐ and ER Stress‐Induced Ca²⁺ Accumulation and Mitochondrial ROS Production

Abstract

Anthocyanins from the petals of <i>Hibiscus syriacus</i> L. (PS) possess anti-inflammatory, antioxidant, and antimelanogenic activities. However, it remains unclear whether PS inhibit the NLR family pyrin domain-containing 3 (NLRP3) inflammasome activation and assembly. This study is aimed at investigating whether PS downregulate NLRP3-mediated inflammasome by inhibiting nuclear factor-<i>κ</i>B (NF-<i>κ</i>B) and endoplasmic reticulum (ER) stress. BV2 microglia cells were treated with PS in the presence of lipopolysaccharide and adenosine triphosphate (LPS/ATP), and the NLRP3-related signaling pathway was investigated. In this study, we found that LPS/ATP treatment activated the NLRP3 inflammasome, which resulted in the release of interleukin-1<i>β</i> (IL-1<i>β</i>) and IL-18. Meanwhile, PS reduced LPS/ATP-mediated NLRP3 inflammasome at 12 h by inhibiting ER stress-mediated Ca²⁺ accumulation and subsequent mitochondrial reactive oxygen species (mtROS) production, which, in turn, decreased IL-1<i>β</i> and IL-18 release. Furthermore, PS inhibited the NLRP3 inflammasome 1 h after LPS/ATP treatment by suppressing the NF-<i>κ</i>B pathway, which downregulated Ca²⁺ accumulation and mtROS production. These data showed that PS negatively regulated activation of the NLRP3 inflammasome in a time-different manner by inhibiting the NF-<i>κ</i>B signaling pathway in the early stage and the ER stress response in the late stage. The pathways shared Ca²⁺ accumulation-mediated mtROS production, which was significantly inhibited in the presence of PS. In conclusion, our results suggested that PS has potential as a supplement against NLRP3 inflammasome-related inflammatory disorders; nevertheless, further studies are needed to determine the effect of PS in the noncanonical NLRP3 inflammasome pathways and pathological conditions in vivo.