Multidimensional endotyping in patients with severe asthma reveals inflammatory heterogeneity in matrix metalloproteinases and chitinase 3-like protein 1

Abstract

Background: Disease heterogeneity in patients with severe asthma and its relationship to inflammatory mechanisms remain poorly understood.

Objective: We aimed to identify and replicate clinicopathologic endotypes based on analysis of blood and sputum parameters in asthmatic patients.

Methods: One hundred ninety-four asthmatic patients and 21 control subjects recruited from 2 separate centers underwent detailed clinical assessment, sputum induction, and phlebotomy. One hundred three clinical, physiologic, and inflammatory parameters were analyzed by using topological data analysis and Bayesian network analysis.

Results: Severe asthma was associated with anxiety and depression, obesity, sinonasal symptoms, decreased quality of life, and inflammatory changes, including increased sputum chitinase 3-like protein 1 (YKL-40) and matrix metalloproteinase (MMP) 1, 3, 8, and 12 levels. Topological data analysis identified 6 clinicopathobiologic clusters replicated in both geographic cohorts: young, mild paucigranulocytic; older, sinonasal disease; obese, high MMP levels; steroid resistant TH2 mediated, eosinophilic; mixed granulocytic with severe obstruction; and neutrophilic, low periostin levels, severe obstruction. Sputum IL-5 levels were increased in patients with severe particularly eosinophilic forms, whereas IL-13 was suppressed and IL-17 levels did not differ between clusters. Bayesian network analysis separated clinical features from intricately connected inflammatory pathways. YKL-40 levels strongly correlated with neutrophilic asthma and levels of myeloperoxidase, IL-8, IL-6, and IL-6 soluble receptor. MMP1, MMP3, MMP8, and MMP12 levels were associated with severe asthma and were correlated positively with sputum IL-5 levels but negatively with IL-13 levels.

Conclusion: In 2 distinct cohorts we have identified and replicated 6 clinicopathobiologic clusters based on blood and induced sputum measures. Our data underline a disconnect between clinical features and underlying inflammation, suggest IL-5 production is relatively steroid insensitive, and highlight the expression of YKL-40 in patients with neutrophilic inflammation and the expression of MMPs in patients with severe asthma.

Keywords: Asthma; chitinase 3–like protein 1; cytokines; endotype; eosinophils; heterogeneity; matrix metalloproteinase; neutrophils; phenotype; topological data analysis.

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Fig 1

Protease/antiprotease balance in asthmatic patients. MMP/tissue inhibitor of metalloproteinases (TIMP-1) ratios in sputum in asthmatic patients compared with healthy subjects for MMP1 (A), MMP3 (B), MMP8 (C), and MMP12 (D) are shown. Horizontal lines show medians. Statistical comparisons were done with Student t tests on log-transformed data.

Fig 2

Multidimensional clinicopathological clusters in asthmatic patients in the derivation data set (Southampton cohort). A topological network generated by using 22 clinical and pathological features together identifies 1 healthy (in blue) and 8 distinct clinicopathobiologic asthma clusters (A-H). The network is colored according to ACQ7 scores, with the most symptomatic subjects in red. The TDA used 145 subjects with the most complete data: metric, variance-normalized Euclidean; lenses, principal and secondary singular value decomposition (resolution, 30; gain, 3.0/3.0×, equalized) and presence/absence of asthma; node size, proportional to the number of subjects in the node. Color bars: red, highest ACQ7 score; blue, healthy participants. Features in boldface were replicated in the validation data set. GINA, Global Initiative for Asthma.

Fig 3

Bayesian belief network showing the strongest interactions between pathobiologic parameters across a range of clinical severities of asthma or health. Nodes without strong interactions are excluded. Line thickness represents the strength of the interaction (Euclidean distance). Line colors: green, positive associations; red, negative associations; black, nonlinear associations. AQLQ, Juniper Asthma Quality of Life Questionnaire; BD, bronchodilator; FGF, fibroblast growth factor; GCSF, Granulocyte-colony stimulating factor; GINA, Global Initiative for Asthma; MPO, myeloperoxidase; SPT, skin prick test; VEGF, vascular endothelial growth factor.

Fig 4

Inflammatory mediators associated with sputum YKL-40 levels. Spearman correlations between levels of sputum YKL-40 and sputum myeloperoxidase (MPO; A), IL-8 (B), vascular endothelial growth factor (VEGF; C), elastase (D), IL-6 soluble receptor (IL-6SR; E), IL-6 (F), neutrophils (G), and serum YKL-40 (H) are shown.