An Emerging Role for Exhaled Nitric Oxide in Guiding Biological Treatment in Severe Asthma

Asthma is a heterogeneous disease with regard to the inflammatory pathways activated. In recent years, biologic drugs (monoclonal antibodies) directed towards specific components of type 2 inflammation have been approved for the treatment of severe asthma. Phenotyping of patients with severe asthma and evaluation of biomarkers have been recommended to help identify patients who are candidates for treatment with biologics and to monitor treatment responses. Fractional exhaled Nitric Oxide (FeNO) is a biomarker of type 2 inflammation in asthma, signaling activation of Interleukin (IL)-4/IL-13 pathway. FeNO could be useful to assess treatment response or identify candidates for a specific drug that acts on type 2 inflammation mechanisms linked to Nitric Oxide (NO) production, such as the IL-4/IL-13 pathway or upstream processes. The value of FeNO as a biomarker predictive of responses to the biologics available for treating severe asthma is discussed based on the published studies at the moment of the review.