Sputum SLC40A1 as a Novel Biomarker is Increased in Patients with Acute Exacerbation of Chronic Obstructive Pulmonary Disease

Solute carrier family 40 member 1 (SLC40A1 or Ferroportin) is a cell surface glycoprotein that participates in the efflux of cellular iron and disease pathogenesis. Induced sputum is a non-invasive method for lung sample collection. However, it remains unknown whether SLC40A1 is a potential diagnostic biomarker in induced sputum cells of patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD). We in this study aimed to investigate the expression and the anti-inflammatory role of SLC40A1 in the induced-sputum cells of AECOPD patients.

A total of 35 induced sputum samples were collected from patients with AECOPD. Flow cytometry analysis was used to determine inflammatory cell phenotypes and SLC40A1 expression. Murine RAW 264.7 cell lines were treated with cigarette smoke extract (CSE) and SLC40A1-shRNA for SLC40A1 expression in vitro. ELISA was used for measurement of pro-inflammatory cytokine expression in vitro.

Flow cytometry analysis showed that sputum neutrophils were increased in AECOPD patients with 3-5 exacerbations per year compared to 1 exacerbation per year, accompanied by elevated expression of CD40 and SLC40A1 in macrophages. The lung function (FEV1%pred) was reduced with a higher COPD exacerbation rate. There was a negative correlation between the FEV1% predicted and sputum neutrophil count. Patients expressing high levels of SLC40A1 exhibited higher exacerbation rates. SLC40A1 expression levels positively correlated with sputum neutrophils and negatively correlated with predicted FEV1%. In addition, mechanical ventilation reduces sputum neutrophils and SLC40A1 expression, particularly in patients with a high exacerbation rate. Further analysis in RAW 264.7 macrophage cell lines showed that cigarette smoke extract (CSE) increased the expression of SLC40A1, TNF-α, IL-6 and IL-10 at a concentration-dependent manner. SLC40A1 knockdown increased the expression of TNF-α and IL-6 and reduced the expression of IL-10 in CSE-treated macrophages.

SLC40A1 in sputum macrophages is increased and closely related to AECOPD severity, it would be a potential anti-inflammatory biomarker of patients with AECOPD.