Hyperbaric oxygen enhances neutrophil apoptosis and their clearance by monocyte-derived macrophages

Abstract

Neutrophil apoptosis and clearance by macrophages are essential for wound healing. Evidence suggests that hyperbaric oxygen (HBO) exposure may enhance neutrophil apoptosis, but HBO effects leading to neutrophil clearance by macrophages are still unclear. In the current study, bovine neutrophils and monocyte-derived macrophages (MDMФ) were co-cultured under HBO (97.9% O2, 2.1% CO2 at 2.4 ATA), hyperbaric normoxia (8.8% O2 at 2.4 ATA), normobaric hyperoxia (95% O2, 5% CO2), normoxia (air) and normobaric hypoxia (5% O2, 5% CO2). Phagocytosis of fresh and 22 h-aged neutrophils by MDMФ was increased after HBO pre-treatment, assessed using flow cytometry and light microscopy. Enhanced clearance of neutrophils was accompanied by an increase in H2O2 levels following HBO pre-treatment with up regulation of IL-10 (anti-inflammatory cytokine) mRNA expression in LPS-stimulated MDMФ that had ingested aged neutrophils. TNF-α (pro-inflammatory cytokine) gene expression did not change in LPS-stimulated MDMФ that had ingested fresh or aged neutrophils after HBO, pressure and hyperoxia. These findings suggest that HBO-activated MDMФ participate in the clearance of apoptotic cells. Uptake of neutrophils by MDMФ exposed to HBO may contribute to resolution of inflammation, because HBO induced up-regulation of IL-10 mRNA expression.