Neutrophil elastase-dependent cleavage of LTA4H alters its aminopeptidase activity in cystic fibrosis

The enzyme leukotriene A4 hydrolase (LTA4H) is classically known for its epoxide hydrolase activity that converts leukotriene A4 (LTA4) to the neutrophil chemoattractant LTB4 [1]. In 2010, our group published a study in Science that demonstrated that during an influenza model of acute airway inflammation, LTA4H was released from cells to degrade proline-glycine-proline (PGP), a non-canonical CXCR1 and -2 agonist of polymorphonuclear neutrophil (PMN) recruitment and activation [2], thereby attenuating PMN inflammation [3].

This study demonstrates that neutrophil elastase is a major enzyme responsible for the regulation of leukotriene A4 hydrolase (LTA4H) upon neutrophil activation, altering the aminopeptidase activity of LTA4H in the cystic fibrosis lung https://bit.ly/3SS1tKk

Exosomal microRNA predicts and protects against severe bronchopulmonary dysplasia in extremely premature infants

Premature infants are at high risk for developing bronchopulmonary dysplasia (BPD), characterized by chronic inflammation and inhibition of lung development, which we have recently identified as being modulated by microRNAs (miRNAs) and alterations in the airway microbiome. Exosomes and exosomal miRNAs may regulate cell differentiation and tissue and organ development. We discovered that tracheal aspirates from infants with severe BPD had increased numbers of, but smaller, exosomes compared with term controls. Similarly, bronchoalveolar lavage fluid from hyperoxia-exposed mice (an animal model of BPD) and supernatants from hyperoxia-exposed human bronchial epithelial cells (in vitro model of BPD) had increased exosomes compared with air controls. Next, in a prospective cohort study of tracheal aspirates obtained at birth from extremely preterm infants, utilizing independent discovery and validation cohorts, we identified unbiased exosomal miRNA signatures predictive of severe BPD. The strongest signal of reduced miR-876-3p in BPD-susceptible compared with BPD-resistant infants was confirmed in the animal model and in vitro models of BPD. In addition, based on our recent discovery of increased Proteobacteria in the airway microbiome being associated with BPD, we developed potentially novel in vivo and in vitro models for BPD combining Proteobacterial LPS and hyperoxia exposure. Addition of LPS led to a larger reduction in exosomal miR 876-3p in both hyperoxia and normoxia compared with hyperoxia alone, thus indicating a potential mechanism by which alterations in microbiota can suppress miR 876-3p. Gain of function of miR 876-3p improved the alveolar architecture in the in vivo BPD model, demonstrating a causal link between miR 876-3p and BPD. In summary, we provide evidence for the strong predictive biomarker potential of miR 876-3p in severe BPD. We also provide insights on the pathogenesis of neonatal lung disease, as modulated by hyperoxia and microbial product-induced changes in exosomal miRNA 876-3p, which could be targeted for future therapeutic development.

Absorbance and redox based approaches for measuring free heme and free hemoglobin in biological matrices

Cell-free heme (CFH) and hemoglobin (Hb) have emerged as distinct mediators of acute injury characterized by inflammation and microcirculatory dysfunction in hemolytic conditions and critical illness. Several reports have shown changes in Hb and CFH in specific pathophysiological settings. Using PBS, plasma from patients with sickle cell disease, acute respiratory distress syndrome (ARDS) patients and supernatants from red cells units, we found that commonly used assays and commercially available kits do not distinguish between CFH and Hb. Furthermore, they suffer from a variety of false-positive interferences and limitations (including from bilirubin) that lead to either over- or underestimation of CFH and/or Hb. Moreover, commonly used protocols to separate CFH and Hb based on molecular weight (MWt) are inefficient due to CFH hydrophobicity. In this study, we developed and validated a new approach based on absorbance spectrum deconvolution with least square fitting analyses that overcomes these limitations and simultaneously measures CFH and Hb in simple aqueous buffers, plasma or when associated with red cell derived microvesicles. We show how incorporating other plasma factors that absorb light over the visible wavelength range (specifically bilirubin), coupled with truncating the wavelength range analyzed, or addition of mild detergent significantly improves fits allowing measurement of oxyHb, CFH and metHb with >90% accuracy. When this approach was applied to samples from SCD patients, we observed that CFH levels are higher than previously reported and of similar magnitude to Hb.