A Novel Compound Ligusticum Cycloprolactam Alleviates Neuroinflammation After Ischemic Stroke via the FPR1/NLRP3 Signaling Axis

Background: Microglia/macrophages, as pivotal immune cells in the central nervous system (CNS), play a critical role in neuroinflammation associated with ischemic brain injury. Targeting their activation through pharmacological interventions represents a promising strategy to alleviate neurological deficits, thereby harboring significant implications for the prevention and treatment of ischemic stroke. Ligusticum cycloprolactam (LIGc), a novel monomeric derivative of traditional Chinese medicine, has shown potential as a therapeutic agent; however, its specific role in cerebral ischemic injury remains unclear.

Methods: In vitro experiments utilized lipopolysaccharide (LPS)-induced inflammation models of RAW264.7 cells and primary mouse microglia. In vivo studies employed LPS-induced neuroinflammation models in mice and a transient middle cerebral artery occlusion (tMCAO) mouse model to evaluate the impact of LIGc on neuroinflammation and microglia/macrophage phenotypic alterations. Further elucidation of the molecular mechanisms underlying these effects was achieved through RNA-Seq analyses.

Results: LIGc exhibited the capacity to attenuate LPS-induced production of pro-inflammatory markers in macrophages and microglia, facilitating their transition to an anti-inflammatory phenotype. In models of LPS-induced neuroinflammation and tMCAO, LIGc ameliorated pathological behaviors and neurological deficits while mitigating brain inflammation. RNA-seq analyses revealed formyl peptide receptor 1 (FPR1) as a critical mediator of LIGc's effects. Specifically, FPR1 enhances the pro-inflammatory phenotype of microglia/macrophages and inhibits their anti-inflammatory response by upregulating NLR family pyrin domain protein 3 (NLRP3) inflammasomes, thus aggravating inflammatory processes. Conversely, LIGc exerts anti-inflammatory effects by downregulating the FPR1/NLRP3 signaling axis. Furthermore, FPR1 overexpression or NLRP3 agonists reversed the effects of LIGc observed in this study.

Conclusion: Our findings suggest that LIGc holds promise in improving ischemic brain injury and neuroinflammation through modulation of microglia/macrophage polarization. Mechanistically, LIGc attenuates the pro-inflammatory phenotype and promotes the anti-inflammatory phenotype by targeting the FPR1/NLRP3 signaling pathway, ultimately reducing inflammatory responses and mitigating neurological damage.