Icariside II

Chronic asthma features persistent airway inflammation, airway hyper-responsiveness, and structural remodeling. Macrophages, especially alternatively activated M2 cells, are key drivers of type-2 immunity and fibrosis. Icariside II (ICAII), a flavonoid from Epimedium, exhibits known anti-inflammatory properties, but its precise immunomodulatory effects on M2 macrophages in asthma remain elusive.

This work sought to evaluate the potential therapeutic role of ICAII using a mouse model that mimics chronic asthma and define the underlying mechanisms, with emphasis on macrophage polarization and immune-mediated tissue remodeling.

Chronic asthma was established in BALB/c mice through ovalbumin (OVA) sensitization and repeated exposure, followed by ICAII administration at various doses. Pulmonary function tests, histological analyses, ELISA, flow cytometry, and immunohistochemistry were employed to assess inflammation, airway remodeling, and macrophage polarization. In vitro experiments using RAW264.7 and MHS macrophage lines further investigated ICAII's impact on M2 differentiation. Transcriptome sequencing, network pharmacology, molecular docking analyses, and validation were integrated to identify key regulatory pathways.

ICAII improved airway resistance and compliance, alleviated inflammatory infiltration and collagen deposition, and lowered Th2 cytokines, serum IgE, and pro-fibrotic markers, with the most pronounced effects observed at 40 mg/kg. In vivo, ICAII suppressed M2 macrophage accumulation, and in vitro, it inhibited M2 differentiation, while with a divergent impact on M1 marker expression. Network pharmacology and molecular docking predicted a moderate affinity interaction between ICAII and SIRT1, which was experimentally confirmed by SPR and enzymatic activity assays. Combined with transcriptomic and pharmacological analyses, these results identified the SIRT1/NLRP3 and TGF-β/Smad3/VEGF axes as principal pathways mediating the protective effects of ICAII against chronic asthma. Specifically, the SIRT1/NLRP3 axis refers to Sirtuin1 (SIRT1)-mediated suppression of NLR family pyrin domain containing 3 (NLRP3) inflammasome activation, whereas the TGF-β/Smad3/VEGF axis represents a transforming growth factor beta-driven profibrotic signaling cascade associated with vascular endothelial growth factor. Mechanistically, ICAII enhanced SIRT1 activity, suppressed NLRP3 inflammasome-associated inflammation, and inhibited the profibrotic TGF-β/Smad3 signaling cascade and its remodeling-associated downstream effector VEGF, thereby restraining M2 macrophage polarization and tissue remodeling.

We provide the first integrated mechanistic evidence in chronic asthma that ICAII reprograms M2 macrophages via a dual-axis strategy, simultaneously activating SIRT1 to suppress the NLRP3 inflammasome and attenuating TGF-β/Smad3/VEGF-driven remodeling. Unlike previous reports that only described the broad anti-inflammatory effects of ICAII, our study uniquely links immune modulation with structural protection and further delivers direct target engagement validation. This drug-target-function continuum not only delineates a macrophage-centered paradigm for chronic asthma pathobiology but also introduces a translationally actionable mechanism to address the long-standing challenge of persistent airway remodeling and T2-high inflammation.