Untargeted metabolomic profiling identifies disease-specific signatures in food allergy and asthma

Abstract

Background: Food allergy (FA) affects an increasing proportion of children for reasons that remain obscure. Novel disease biomarkers and curative treatment options are strongly needed.

Objective: We sought to apply untargeted metabolomic profiling to identify pathogenic mechanisms and candidate disease biomarkers in patients with FA.

Methods: Mass spectrometry-based untargeted metabolomic profiling was performed on serum samples of children with either FA alone, asthma alone, or both FA and asthma, as well as healthy pediatric control subjects.

Results: In this pilot study patients with FA exhibited a disease-specific metabolomic signature compared with both control subjects and asthmatic patients. In particular, FA was uniquely associated with a marked decrease in sphingolipid levels, as well as levels of a number of other lipid metabolites, in the face of normal frequencies of circulating natural killer T cells. Specific comparison of patients with FA and asthmatic patients revealed differences in the microbiota-sensitive aromatic amino acid and secondary bile acid metabolism. Children with both FA and asthma exhibited a metabolomic profile that aligned with that of FA alone but not asthma. Among children with FA, the history of severe systemic reactions and the presence of multiple FAs were associated with changes in levels of tryptophan metabolites, eicosanoids, plasmalogens, and fatty acids.

Conclusions: Children with FA have a disease-specific metabolomic profile that is informative of disease mechanisms and severity and that dominates in the presence of asthma. Lower levels of sphingolipids and ceramides and other metabolomic alterations observed in children with FA might reflect the interplay between an altered microbiota and immune cell subsets in the gut.

Keywords: Asthma; food allergy; invariant natural killer T cells; metabolites; metabolomics; secondary bile acids; sphingolipids; tryptophan.

Fig. 1.

Heat-map of metabolites significantly different (p<0.005) between FA children and non-atopic controls. For each metabolite, a colorimetric representation of relative expression in each sample is shown according to the scale depicted on top. Metabolites are grouped into main dysregulated pathways and a miscellaneous category.

Fig. 2.

Heat-map of metabolites significantly different (p<0.005) between FA and asthmatic children. For each metabolite, a colorimetric representation of relative expression in each sample is shown according to the scale depicted on top. Metabolites are grouped into main dysregulated pathways and a miscellaneous category.

Fig. 3.

Sphingolipid alterations are prominent in FA. Pairwise comparison of sphingomyelin (3 A,C) and ceramide (3 B,D) metabolites between children with FA and either asthmatic or non-atopic children as well between FA children with and without history of anaphylaxis treated with epinephrine are shown. Mean and SEM are shown. *p≤0.05, ** p≤0.005

Fig. 4.

Circulating iNKT cells are unchanged in FA. 4A. Gating strategy for NK, NKT and iNKT cells. 4B. Proportions of NK, NKT and iNKT cells in children with FA, asthma, FA and asthma, and non-atopic controls. * p≤0.05

Fig.5.

Tryptophan metabolism is dysregulated in children with multiple FA and history of anaphylaxis. The three branches of tryptophan metabolism are depicted together with pairwise comparisons of metabolites significantly different in children with multiple FA or history of anaphylaxis. Mean and SEM are shown. * p≤0.05, ** p≤0.005

Fig. 6.

Differences in bile acid ratios between children with FA and asthma. A schematic representation of bile acid metabolism in the liver and the gut is depicted, followed by pairwise comparison of differentially altered bile acid ratios between asthmatic and food allergic children. Mean and SEM are shown. * p≤0.05, ** p≤0.005