Abstract Rationale Airway inflammation increases with asthma exacerbations through upregulation of inducible nitric oxide synthase (iNOS) in airway epithelial cells. Assessing asthma loss-of-control is difficult during acute exacerbations and there exists a need for a biomarker of asthma control. We evaluated flavin mononucleotide (FMN), a fluorescent cofactor of iNOS and mitochondrial complex I and riboflavin metabolite, as a biomarker during asthma exacerbations. We hypothesize that FMN levels decrease during exacerbation, reflecting mitochondrial stress and increased nitric oxide production. Methods Serum samples were collected from 8 healthy individuals and 34 severe asthmatics at baseline, within 72 hours of an acute exacerbation, and at recovery (6–8 weeks later), as part of the Severe Asthma Research Program (SARP) III UW-Madison ancillary study. Separately, serum and BALF from 21 allergic asthmatics were collected before and 48-hours-post segmental bronchial allergen challenge (SBP-Ag). Bronchial epithelial cells (BECs) from bronchial brushings (3 healthy, 4 non-severe asthmatics, and 4 severe asthmatics) were cultured at air-liquid interface. FMN was quantified using a fluorescence spectrometry protocol (PPR361907) and normalized to total protein. Gene expression was quantified via RT-qPCR. FMN levels were compared using one-way ANOVA and paired t-tests with significance established at p 0.05. Results Serum FMN levels decreased during exacerbation compared to baseline (p = 0.0586, n = 34) and significantly increased at recovery compared to the acute visit (p = 0.006, n = 34). Serum FMN levels following SBP-Ag did not differ from pre-challenge levels. However, there was a significant decrease in BALF FMN following SBP-Ag (p 0.0001, n = 21). Baseline BALF FMN was significantly lower in mild asthmatics (n = 21) compared to healthy (p = 0.0417, n = 10) and severe (p = 0.0002, n = 5) asthmatics at baseline. Similarly, FMN from BECs was lowest in cells from non-severe asthmatics (n = 4, p = 0.0498, compared to healthy). Gene expression of FMN metabolism (Figure 1) as well as riboflavin transporters (RFVT1-3) were not statistically different between healthy, non-severe, and severe asthmatics but trended to favor decreased FMN in BECs from non-severe asthmatics. NOS2 (iNOS gene) was significantly upregulated in severe (n = 4) vs. healthy (p = 0.0492, n = 3). Conclusions FMN may serve as a potential biomarker during asthma exacerbations. Dynamic changes in serum and BALF following viral- and allergen-induced exacerbations suggest a role for FMN in distinguishing T2 and non-T2 asthma phenotypes. With further study, FMN may serve as a diagnostic tool and therapeutic target in asthma. Future studies should investigate the mitochondrial signaling pathways in FMN as a potential explanation for mitochondrial dysfunction observed in asthma. This abstract is funded by: Foundation for Anesthesia Education and Research Mentored Research Training Grant (EAT), University of Wisconsin Department of Anesthesiology Research and Development Fund (EAT), Foundation for Anesthesia Education and Research Medical Student Anesthesia Research Fellowship (CG), William and Judith Busse Professorship (LCD), HL115118(LCD), HL123284 (MR)
Steffan et al. (Fri,) studied this question.