Isoorientin Inhibits Inflammation in Macrophages and Endotoxemia Mice by Regulating Glycogen Synthase Kinase 3β

Isoorientin has anti-inflammatory effects; however, the mechanism remains unclear. We previously found isoorientin is an inhibitor of glycogen synthase kinase 3 beta (GSK3 beta) in vitro. Overactivation of GSK3 beta is associated with inflammatory responses. GSK3 beta is inactivated by phosphorylation at Ser9 (i.e., p-GSK3 beta). Lithium chloride (LiCl) inhibits GSK3 beta and also increases p-GSK3 beta (Ser9). The present study investigated the anti-inflammatory effect and mechanism of isoorientin via GSK3 beta regulation in lipopolysaccharide- (LPS-) induced RAW264.7 murine macrophage-like cells and endotoxemia mice. LiCl was used as a control. While AKT phosphorylates GSK3 beta, MK-2206, a selective AKT inhibitor, was used to activate GSK3 beta via AKT inhibition (i.e., not phosphorylate GSK3 beta at Ser9). The proinflammatory cytokines TNF-alpha, IL-6, and IL-1 beta were detected by ELISA or quantitative real-time PCR, while COX-2 by Western blotting. The p-GSK3 beta and GSK3 beta downstream signal molecules, including NF-kappa B, ERK, Nrf2, and HO-1, as well as the tight junction proteins ZO-1 and occludin were measured by Western blotting. The results showed that isoorientin decreased the production of TNF-alpha, IL-6, and IL-1 beta and increased the expression of p-GSK3 beta in vitro and in vivo, similar to LiCl. Coadministration of isoorientin and LiCl showed antagonistic effects. Isoorientin decreased the expression of COX-2, inhibited the activation of ERK and NF-kappa B, and increased the activation of Nrf2/HO-1 in LPS-induced RAW264.7 cells. Isoorientin increased the expressions of occludin and ZO-1 in the brain of endotoxemia mice. In summary, isoorientin can inhibit GSK3 beta by increasing p-GSK3 beta and regulate the downstream signal molecules to inhibit inflammation and protect the integrity of the blood-brain barrier and the homeostasis in the brain.