Metabolomics identifies disturbances in arginine, phenylalanine, and glycine metabolism as differentiating features of exacerbating atopic asthma in children

Abstract

Background: Asthma exacerbations are highly prevalent in children, but only a few studies have examined the biologic mechanisms underlying exacerbations in this population.

Objective: High-resolution metabolomics analyses were performed to understand the differences in metabolites in children with exacerbating asthma who were hospitalized in a pediatric intensive care unit for status asthmaticus. We hypothesized that compared with a similar population of stable outpatients with asthma, children with exacerbating asthma would have differing metabolite abundance patterns with distinct clustering profiles.

Methods: A total of 98 children aged 6 through 17 years with exacerbating asthma (n = 69) and stable asthma (n = 29) underwent clinical characterization procedures and submitted plasma samples for metabolomic analyses. High-confidence metabolites were retained and utilized for pathway enrichment analyses to identify the most relevant metabolic pathways that discriminated between groups.

Results: In all, 118 and 131 high-confidence metabolites were identified in positive and negative ionization mode, respectively. A total of 103 unique metabolites differed significantly between children with exacerbating asthma and children with stable asthma. In all, 8 significantly enriched pathways that were largely associated with alterations in arginine, phenylalanine, and glycine metabolism were identified. However, other metabolites and pathways of interest were also identified.

Conclusion: Metabolomic analyses identified multiple perturbed metabolites and pathways that discriminated children with exacerbating asthma who were hospitalized for status asthmaticus. These results highlight the complex biology of inflammation in children with exacerbating asthma and argue for additional studies of the metabolic determinants of asthma exacerbations in children because many of the identified metabolites of interest may be amenable to targeted interventions.

Keywords: Arginine; asthma control; asthma exacerbation; asthma in children; glycine; inflammation; metabolomics; phenylalanine; status asthmaticus.

Fig 1

A and B, PLS-DA of metabolites from positive mode (A) and negative mode (B) that discriminated between exacerbating asthma (red circles) and stable asthma (green circles) in children. The number in parentheses reflects the variance explained by each component.

Fig 2

A and B, VIP score plot of normalized metabolites by group in positive mode (A) and negative mode (B). Higher concentrations are in red and lower concentrations are in blue.

Fig 3

Scatterplots of normalized concentrations of the top 12 metabolites explaining the variable importance of projection (VIP) of the first component in the PLS-DA. Data reflect either positive or negative mode for prolylleucine (A), trans-4-hydroxy-L-proline (B), hydroquinone (C), acetylcholine (D), 2-hydroxybutyrate (E), 3-methyl-L-histidine (F), L-ergothioneine (G), citrulline (H), O-acetylcarnitine (I), 3-(2-hydroxyphenyl) propanoate (J), 3-methylxanthine (K), and 3-methyl-2-oxovalerate (L).

Fig 4

Pathway enrichment analysis showing the differences between children with exacerbating versus stable asthma. Significant metabolic pathways with an impact of .05 or higher are shown. tRNA, Transfer RNA.

Fig 5

Interconnectedness of significant pathways from pathway enrichment analysis. Metabolites with concentrations that were decreased in children with exacerbating asthma are shown in red, metabolites with concentrations that were increased are shown in green. Metabolites that were identified but did not differ in terms of concentration are shown in blue, and metabolites that were not identified by our methods are shown in black.

Fig 6

Scatterplots of normalized concentrations of 5 significant (of 9 in total) metabolites assessed in a validation sample of outpatient children with uncontrolled and stable asthma, including 3-(2-hydroxyphenyl) propanoate (A), trans-4-hydroxy-L-proline (B), acetyl-β-methylcholine (C), 3-methyl-L-histidine (D), and citrulline (E).