Low density neutrophils are new inflammatory players in heart failure: role of neutrophil extracellular traps (nets)

Circulating neutrophils regroup two subtypes: high- and low-density neutrophils (HDNs and LDNs). LDNs count represents about 2% of total neutrophil under physiological conditions, but is increased in multiple pathologies and have a higher capacity to release pro-inflammatory cytokines and neutrophil extracellular traps (NETs). Heart failure either with reduced (HFrEF) or preserved ejection fraction (HFpEF) is characterized by low-grade chronic inflammation. We wanted to determine if LDNs count is increased in HF patients and if their inflammatory properties are enhanced vs HDNs. HDNs and LDNs were isolated from human blood by density gradient and purified by cell sorting. NETs formation (NETosis) was quantified by confocal microscopy. Circulating inflammatory and NETosis biomarkers were measured by ELISA. Neutrophil adhesion onto endothelial cells (ECs) was assessed by optical microscopy. HDNs and LDNs counts were increased up to 39% and 2740% respectively in hospitalized acute decompensated (ADHFpEF) patients vs healthy individuals. In all HF patients, the correlations between LDNs counts and circulating inflammatory (CRP, IL-6 and -8, NT-proBNP, and NETosis components (MPO, MPO-DNA complex and citrullinated histone 3; H3Cit) were all significant. LDNs expressed more MPO, H3Cit and NETs and were more pro-adhesive onto ECs. In summary, increasing circulating LDNs and NETosis components could be considered as new biomarkers of inflammation severity in HF patients.