Cytokine and Metabolomic Signatures of Mepolizumab Response Across Upper and Lower Airway Compartments in Severe Eosinophilic Asthma: An Exploratory Analysis

<b>Background</b>: Mepolizumab improves asthma control in severe eosinophilic asthma (SEA). However, its multidimensional effects on airway and systemic biomarkers are still incompletely understood. <b>Methods</b>: In this prospective study, 15 SEA patients were evaluated at baseline (T₀), 6 (T₆), and 12 months (T₁₂) after starting mepolizumab. Lung function, FeNO values, asthma control, blood eosinophil count (BEC), cytokines, and metabolomic profiles (¹H-NMR) were evaluated in serum, nasal secretions, and exhaled breath condensate (EBC). Univariate and multivariate (PCA, OPLS-DA) analyses were performed. <b>Results</b>: Mepolizumab reduced exacerbations, from a median of 2 at T₀ to 0 at both T₆ (<i>p</i> = 0.001) and T₁₂ (<i>p</i> = 0.003). ACT improved from 18.7 ± 4.7 at baseline to 23.0 ± 2.8 at T₆ (<i>p</i> = 0.026) and 23.4 ± 3.3 at T₁₂ (<i>p</i> = 0.032), while FEV₁ increased by 270 mL at T₆ (<i>p</i> = 0.032) and remained stable at T₁₂. Median BEC decreased from 450.0 (350.0-560.0) to 65.0 (50.0-87.5) cells/μL at T₆ and to 50.0 (35.0-160.0) at T₁₂ (<i>p</i> < 0.001), while FeNO showed a non-significant downward trend. IL-13 significantly decreased in serum and nasal secretions at T₆ and T₁₂, while IL-5 increased in nasal secretions at both timepoints and remained unchanged in serum. IL-2 showed opposite trends in serum and nasal samples, whereas GM-CSF and IFN-γ increased in nasal secretions at T₁₂. Metabolomic profiling suggested compartment-specific changes, with decreased short-chain alcohols in EBC, increased amino acids in nasal secretions and serum at T₆, and elevated pyruvate in serum at T₁₂, although none reached statistical significance in univariate analysis. <b>Conclusions</b>: Mepolizumab induced consistent clinical, immunologic, and metabolic changes across compartments, supporting the use of integrated cytokine and ¹H-NMR metabolomic profiling as a complementary approach for response assessment in SEA.