Efficacy of different doses of methylprednisolone on AECOPD mice induced by influenza A virus infection

Objective‍ ‍To investigate the efficacy of varying doses of methylprednisolone (MP) on mice with acute exacerbations of chronic obstructive pulmonary disease (AECOPD) induced with influenza A virus (IAV). Methods‍ ‍Mouse model of COPD was established using LPS combined with smoking for 12 weeks, and then these COPD mice were treated with administration of 40 μL IAV via nasal drip to establish a AECOPD model. A total of 15 AECOPD mice were randomly divided into low-, medium- and high-dose MP groups, oseltamivir group and blank group. The body weight and survival time were monitored within 10 d after IAV infection. On days 1, 3, and 5 post-treatment, lung function was assessed using whole-body plethysmography (WBP), inflammatory factors in bronchoalveolar lavage fluid (BALF) were quantified with ELISA, viral titers in BALF were determined using plaque assays, and colony-forming units were evaluated with blood agar plates. Immunofluorescence analysis: ①Pulmonary immunofluorescence assay: Mice were randomly categorized into (n=4): LPS 1-day group, LPS 3-day group, and LPS+MP treatment group. All groups received an initial dose of LPS via atomization; subsequently, the LPS+MP treatment group received a single gavage dose of MP. Lung tissues were harvested from the 1-day LPS group on 1 d post-treatment, and from the 3-day LPS and LPS+MP groups on 3 d for immunofluorescence staining. ②Cellular immunofluorescence assay: Mouse bone marrow neutrophils were classified into blank control (no intervention), LPS stimulation (LPS group), MP intervention with LPS stimulation (LPS+MP group), and MP intervention alone (MP group). The above cells were collected in 4 h after corresponding interventions for subsequent cellular immunofluorescence analysis. Results‍ ‍①The medium-dose MP group demonstrated the most significant improvement in survival rate, weight recovery, and lung function when compared to other groups (P<0.05). ② Treatment of medium-dose MP obviously reduced the levels of IL-6 and neutrophil extracellular traps (NETs) (P<0.05), while, elevated inflammatory factors and NETs were observed in the high-dose MP group on day 5 post-treatment. ③ Notable decline in the lung injury score was found in the medium-dose MP group than the other groups (P<0.05). ④The high-dose MP group exhibited substantial bacterial proliferation and delayed viral clearance since day 5 after treatment. Conclusion‍ ‍Medium-dose MP shows best efficacy in treatment of IAV-induced AECOPD, and the dose neither delays viral clearance nor increases the risk of bacterial infection following viral infection.