Decreased expression of indolamine 2,3-dioxygenase in childhood allergic asthma and its inverse correlation with fractional concentration of exhaled nitric oxide.

Background: The tryptophan metabolic pathway mediated by indolamine 2,3-dioxygenase (IDO), a tryptophan-degrading enzyme, plays an important role in controlling the development of allergic inflammation. The fractional concentration of exhaled nitric oxide (FeNO) is closely associated with the allergic state and is extensively used for the clinical evaluation of airway allergic inflammation. Clinical trials have rarely assessed the expression of IDO in childhood allergic asthma and its correlation with FeNO.

Objective: To evaluate the IDO level in children with childhood allergic asthma and the relation between IDO levels and FeNO.

Methods: Thirty children older than 5 years who were diagnosed the first time with allergic asthma were selected from the pediatric outpatient department. Another 30 healthy children were selected as controls. The subjects were evaluated by complete medical history, pulmonary function test results, skin prick test reaction, FeNO concentration test result, eosinophil count, and a disease severity score. Peripheral venous blood and induced sputum were obtained to measure the concentrations of IDO metabolites (ie, tryptophan and kynurenine).

Results: The IDO levels in the peripheral blood and induced sputum were significantly lower in patients with childhood allergic asthma than in children in the control group. The IDO level was negatively correlated with FeNO but was not significantly correlated with age, sex, blood eosinophil count, or disease severity scale.

Conclusion: The expression of IDO was significantly lower in childhood allergic asthma, particularly in children with high FeNO levels. There was no significant relation between IDO levels and asthma severity.

Trial Registration: Chinese Clinical Trial Register (www.chictr.org.cn) Identifier: ChiCTR-COC-15006080.