Abstract
Background. Animal models using intratracheal instillation show that elastase, unopposed by α1-antitrypsin (AAT) causes alveolar damage and hemorrhage associated with emphysematous changes.
Aim. To characterize any relationship between alveolar hemorrhage and human AAT deficiency (AATD) using bronchoalveolar lavage (BAL) and lung explant samples from AATD subjects.
Methods. BAL samples (17 patients, 15 controls) were evaluated for free heme (iron protoporphyrin IX) and total iron concentrations. Alveolar macrophage (AlvMac) activation patterns were assessed by RNA sequencing and validated in vitrousing heme-stimulated, monocyte-derived macrophages (MDM). Lung explants (7 patients, 4 controls) were assessed for iron sequestration protein expression patterns using Prussian blue stain and ferritin immunohistochemistry, as well as ferritin iron imaging and elemental analysis by transmission electron microscopy (TEM). Tissue oxidative damage was assessed using 8-hydroxy-2'-deoxyguanosine (8-OHdG) immunohistochemistry.
Results. BAL collected from AATD patients showed significantly elevated free heme and total iron concentrations. Alveolar and interstitial macrophages in AATD explants showed elevated iron and ferritin accumulation in large lysosomes packed by iron oxide cores with degraded ferritin protein cages. BAL macrophage RNA sequencing showed innate proinflammatory activation, replicated in vitro by hemin exposure, that also triggered reactive oxygen species generation. AATD explants showed massive oxidative DNA damage in both lung epithelial cells and macrophages.
Conclusions. BAL and tissue markers of alveolar hemorrhage, together with molecular and cellular evidence of macrophage innate pro-inflammatory activation and oxidative damage, are consistent with free heme stimulation. Overall, this initial study provides evidence for a pathogenetic role of elastase-induced alveolar hemorrhage in AATD emphysema.
Footnotes
This manuscript has recently been accepted for publication in the ERJ Open Research. It is published here in its accepted form prior to copyediting and typesetting by our production team. After these production processes are complete and the authors have approved the resulting proofs, the article will move to the latest issue of the ERJOR online. Please open or download the PDF to view this article.
This is a PDF-only article. Please click on the PDF link above to read it.
- Copyright ©The authors 2023
This version is distributed under the terms of the Creative Commons Attribution Non-Commercial Licence 4.0. For commercial reproduction rights and permissions contact permissions{at}ersnet.org
