Isorhamnetin alleviates lipopolysaccharide-induced inflammatory responses in BV2 microglia by inactivating NF-κB, blocking the TLR4 pathway and reducing ROS generation

摘要

Isorhamnetin, which is a flavonoid predominantly found in fruits and leaves of various plants, including Hippophae rhamnoides L. and Oenanthe javanica (Blume) DC, is known to possess various pharmacological effects. However, the anti?inflammatory potential of isorhamnetin remains poorly studied. Therefore, the present study aimed to investigate the inhibitory potential of isorhamnetin against inflammatory responses in lipopolysaccharide (LPS)?stimulated BV2 microglia. To measure the effects of isorhamnetin on inflammatory mediators and cytokines, and reactive oxygen species (ROS) generation, the following methods were used: cell viability assay, griess assay, ELISA, reverse transcriptase?polymerase chain reaction, flow cytometry, western blotting and immunofluorescence staining. The results revealed that isorhamnetin significantly suppressed LPS?induced secretion of pro?inflammatory mediators, including nitric oxide (NO) and prostaglandin E2, without exhibiting significant cytotoxicity. Consistent with these results, isorhamnetin inhibited LPS?stimulated expression of regulatory enzymes, including inducible NO synthase and cyclooxygenase?2 in BV2 cells. Isorhamnetin also downregulated LPS?induced production and expression of pro?inflammatory cytokines, such as tumor necrosis factor?α and interleukin?1β. The mechanism underlying the anti?inflammatory effects of isorhamnetin was subsequently evaluated; this flavonoid inhibited the nuclear factor (NF)?κB signaling pathway by disrupting degradation and phosphorylation of inhibitor κB?α in the cytoplasm and blocking translocation of NF?κB p65 into the nucleus. In addition, isorhamnetin effectively suppressed LPS?induced expression of Toll?like receptor 4 (TLR4) and myeloid differentiation factor 88. It also suppressed the binding of LPS with TLR4 in BV2 cells. Furthermore, isorhamnetin markedly reduced LPS?induced generation of ROS in BV2 cells, thus indicating a strong antioxidative effect. Collectively, these results suggested that isorhamnetin may suppress LPS?mediated inflammatory action in BV2 microglia through inactivating the NF?κB signaling pathway, antagonizing TLR4 and eliminating ROS accumulation. Further studies are required to fully understand the anti?inflammatory effects associated with the antioxidant capacity of isorhamnetin; however, the findings of the present study suggested that isorhamnetin may have potential benefits in inhibiting the onset and treatment of neuroinflammatory diseases.