Pharmacological Effects of Fructus Ligustri Lucidi on Neuroinflammation and Exploration of Active Compound Based on the Interaction with CaSR

Abstract

Background The onset of depression and the lack of effectiveness in antidepressant medication may be related to the overall activation of the neuroinflammatory response. The calcium-sensing receptor (CaSR), widely expressed in various types of cells in the nervous system, participates in inflammatory responses. Our studies had revealed that the extract of Fructus Ligustri Lucidi (FLL) could exert beneficial effects on improving bone metabolism of diabetic rats and mice via acting on renal CaSR. The effects of FLL on neuroinflammation and the role of FLL in protecting from neuropsychiatric diseases remain elusive. The present work aimed to study the pharmacological mechanisms by which FLL and its active compound inhibit neuroinflammation from the view of modulating CaSR. Methods ：Mice were treated with the phenol glycosides extract of FLL for 14 consecutive days before intraperitoneally injected with lipopolysaccharide (LPS) on the 15th day to establish acute model of depression. The allosteric sites of CaSR were predicted and its interaction with phenol glycosides was analyzed by Schördinger Maestro package. After treatment of streptozotocin-induced diabetic mice with ligustroflavone for 8 weeks, calcium balance and bone properties as well as renal CaSR signaling were measured. BV2 microglia cells were incubated with different doses of ligustroflavone before CaSR agonist cinacalcet was added to the medium to stimulate CaSR. The production of inflammatory response, like NLRP3 inflammasome, and the release of IL-1β, MCP-1, and Rantes as well as morphological changes of the cells were detected. Results Pretreatment of mice with the phenol glycosides of FLL inhibited LPS-triggered depression-like behaviors by reducing the release of inflammatory factors and attenuating the neuroinflammation via affecting the CaSR pathway. Phytochemical work clarified the main compounds like ligustroflavone contained in FLL phenol glycosides extract. Docking analysis found that ligustroflavone interacted well with the allosteric site of CaSR and had the potency as CaSR antagonist. Treatment of diabetic mice with ligustroflavone maintained calcium homeostasis by antagonizing CaSR in kidney, consequently protecting from diabetes-induced osteoporosis. Our ongoing study demonstrated that pre-incubation of microglia cells with ligustroflavone significantly inhibited the activation of microglials and repressed the cinacalcet-induced activation of NLRP3 inflammasome signaling and the increase in levels of inflammatory mediators, including cytokines and chemokines, by antagonizing CaSR. Conclusion: FLL exerted beneficial effects on protecting from depressive-like behaviors by suppressing neuroinflammation via acting on CaSR in brain tissue. Ligustroflavone might be a potential active compound as a candidate of CaSR antagonist.