D19-04 Pde4b Inhibitor Nerandomilast Ameliorates Steroid-resistant Asthma by Suppressing Macrophage Extracellular Trap Release

Abstract Rationale Steroid-resistant asthma (SRA) remains a major clinical challenge, driven by neutrophilic inflammation and aberrant macrophage activation. Although macrophage extracellular traps (METs) have emerged as potential contributors to severe asthma, their mechanistic role remains unclear. This study investigates whether the highly selective PDE4B inhibitor Nerandomilast ameliorates SRA by suppressing METs release. Methods This study integrated in vivo and in vitro experiments with bioinformatic analysis. A murine SRA model was induced using ovalbumin (OVA) and complete Freund’s adjuvant (CFA). The therapeutic effects of Nerandomilast were evaluated via bronchoalveolar lavage fluid (BALF) analysis and lung histopathology. Public databases were interrogated to analyze PDE4B expression and METs activity. An LPS-induced METs model in macrophages was established, and METs release was assessed by detecting citrullinated histone H3 (Cit-H3) expression using immunofluorescence and Western blot. Results In a murine steroid-resistant asthma (SRA) model, administration of Nerandomilast significantly reduced total inflammatory cell counts in bronchoalveolar lavage fluid (BALF), with Giemsa staining confirming a marked decrease in neutrophil infiltration. Histological analyses demonstrated that Nerandomilast alleviated inflammatory cell influx and epithelial injury (H&E staining), suppressed goblet cell hyperplasia and mucus production (PAS staining), and attenuated airway remodeling, as evidenced by reduced α-SMA expression (immunohistochemistry) and restored E-cadherin expression (immunofluorescence). Western blotting further confirmed the downregulation of α-SMA and the restoration of E-cadherin and ZO-1 protein levels. Bioinformatic analysis of patient and model data revealed upregulated PDE4B expression and enhanced macrophage extracellular trap (METs) activity in the steroid-resistant phenotype. Mechanistically, immunofluorescence of lung tissue showed that Nerandomilast significantly reduced the co-localization of F4/80+ macrophages and Cit-H3+ METs. In vitro, Nerandomilast did not affect THP-1-derived macrophage viability but strongly suppressed LPS-induced METs formation, as indicated by decreased Cit-H3 expression in both immunofluorescence and Western blot analyses, achieving a level of inhibition comparable to the METs inhibitor Cl-Amidine. Conclusion The PDE4B inhibitor Nerandomilast demonstrates potent therapeutic efficacy in steroid-resistant asthma by suppressing neutrophilic inflammation, restoring epithelial integrity, and inhibiting airway remodeling. Mechanistically, these benefits are achieved through suppression of M1 macrophage polarization and inhibition of METs release, with efficacy comparable to a direct METs inhibitor. These findings provide compelling preclinical evidence for targeting the PDE4B-METs axis as a novel therapeutic strategy for SRA. This abstract is funded by: None