Vicenin-2 Hinders Pro-Inflammatory Response via Targeting the CaMKKβ-AMPK-SIRT1 Axis in Lipopolysaccharide-Stressed THP-1 Cells

Plant secondary metabolites are known to be valuable agents to hamper inflam- mation owing to their multiple mechanisms of action. This study investigates the molecular mechanisms underlying the anti-inflammatory effects of vicenin-2 in lipopolysaccharide (LPS)-stressed THP-1 cells. After ascertaining the safety of vicenin-2 in our in vitro model, we assessed the anti-inflammatory potential of this flavonoid. Indeed, it counteracted the increase of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 levels, as well as the overexpression of both inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2 caused by the exposure of THP-1 cells to LPS. Acknowledged the role of SIRT1 in the inflammatory process, we focused our attention on this enzyme. Our results showed that LPS dramatically decreased the expression of SIRT1, whereas vicenin-2 restored the levels of this enzyme to those of unexposed cells. These effects were also observed in terms of acetylated p53, a SIRT1 substrate. Notably, we observed that vicenin-2 did not act as a direct activator of SIRT1. Therefore, we investigated the potential involvement of AMP-activated protein kinase (AMPK), an upstream activator of SIRT1. Of note, by block- ing AMPK by dorsomorphin, the protective effects of vicenin-2 on SIRT1 expression and activity were lost, suggesting the engagement of this kinase. Consequently, the blockage of AMPK caused a downstream loss of the anti-inflammatory effect of vicenin-2, which was no longer able to decrease both the activation of nuclear factor (NF)-κB and the production of cytokines induced by LPS. Finally, docking simulation suggested that vicenin-2 might act as an activator of Ca2+/calmodulin-dependent protein kinase kinase β (CaMKKβ), one of the regulators of AMPK. Overall, our results suggest that the anti-inflammatory effects of vicenin-2 may be due to the interaction with the CaMKKβ-AMPK-SIRT1 axis.