(386) Myeloperoxidase activity and methionine oxidation products in bronchoalveolar lavage are associated with heightened risk of bronchiectasis in CF infants and toddlers

Background: Lung inflammation characterized by exuberant neutrophil influx and high concentrations of myeloperoxidase (MPO) occurs shortly after birth in cystic fibrosis (CF). MPO is the only enzyme in humans that produces hypochlorous acid (HOCl), a strong and promiscuous oxidant, under physiological conditions. We previously associated methionine sulfoxide (MetO), a HOCl byproduct, with MPO, neutrophils, and bronchiectasis (BE) using bronchoalveolar lavage fluid (BALF) in a cross-sectional study of early CF. Here, we sought to determine the relationship of MPO and oxidized metabolites with the risk of future BE development in early CF patients across a range of ages.

Methods: BALF was prospectively collected from CF patients aged 0-6 years with evidence of BE at 9 years (n=14), and matched CF patients without evidence of BE at 9 years (n=14). MPO enzymatic activity was measured by immunocapture and Amplex Red oxidation assay. Methionine oxidation products were detected using high-resolution mass spectrometry via Q Exactive High Field operated in positive and negative modes following separation by a HILICON iHILIC-(P) Classic HPLC column. We analyzed Spearman correlations of metabolites with MPO, subsetting for 0-2- and 3-6-year ranges and averaging repeated measures.

Results: MPO activity was significantly increased in CF children who developed BE compared to CF children who did not develop BE (mixed effects p=0.0001). MetO and dehydromethionine (dhMet), another methionine oxidation product of HOCl, were both significantly increased in BALF of CF children who developed BE compared to CF children who did not develop BE (mixed effects p=0.0006). dhMet, but not MetO, was also significantly correlated with MPO activity in 0-2-year-olds (Spearman’s r=0.6031, p=0.0014) and 3-6-year-olds (Spearman’s r=0.7351, p=0.0001), without subsetting for future BE development. Subsetting by BE development revealed correlation of MPO and dhMet in 3-6-year-olds who developed BE (r=0.600, p=0.0261).

Conclusions: MPO is active in the airways of CF infants and toddlers, and is higher in patients who develop bronchiectasis later in life. Methionine oxidation products MetO and dhMet, which are linked to MPO activity via HOCl, are associated with future BE development. These data extend prior observations with MetO to dhMet and reveal its association with inter-individual variations in MPO activity. Further study of these pathways may reveal strategies for treating, preventing, and monitoring inflammation in CF.

Acknowledgements: NHMRC SYNERGY Award APP1183640

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