Targeted quantification of identified metabolites between different inflammatory asthma phenotypes and healthy subjects in the validation set
To validate and determine the expression levels of 40 differentially expressed metabolites, which were selected to perform targeted quantification in patients in the validation set. Amongst which, 24 metabolites were significantly differentially expressed between asthma inflammatory phenotypes (Table 2), with 9 of these metabolites reaching a significant P value of .001 or less. Histamine expression was highest but levels of 5-L-glutamyl-L-alanine, nicotinamide, dihydrothymine, L-leucine, L-phenylalanine, alanyl-leucine, phenylalanyl-serine, phenylalanylphenylalanine were the lowest in patients with EA. Expression levels of adenosine 5’-monophosphate, glyceric acid, taurine, dihydrothymine, L-leucine, tyramine, L-glutamate, alanyl-leucine, phenylalanyl-serine, threoninyl-phenylalanine were highest but level of glycerophosphocholine was lowest in patients with NA. Expression levels of glycerophosphocholine, cyclohexylamine, heptadecanoic acid, oleic acid were highest but level of dodecanoic acid was lowest in patients with PGA (Table 2).
Furthermore, those differentially expressed metabolites were examined by receiver operating characteristic (ROC) curves to discriminate different inflammatory asthma phenotypes (Table E4). As a result, taurine, alanyl-leucine, phenylalanyl-serine and threoninyl-phenylalanine could be used as a candidate metabolite marker to discriminate between NA and EA or PGA with the AUC was range from 0.816 to 0.975 (all P< 0.05). However, no single metabolite could satisfactorily discriminate between EA and PGA as all of the AUC < 0.7.