Effects of dextran oxygen-loaded nanodroplets on macrophages inflammatory response during hypoxia

Chronic wounds represent an emerging burden in Western countries, especially in the elderly, because of the lack of suitable, safe and effective therapies. The hypoxic environment, the persistent inflammation, and the bacterial superinfections are some of the main features of chronic ulcers. Dextran oxygen-loaded nanodroplets (OLNDs), composed of a 2H,3H-decafluoropentane inner core binding oxygen and a dextran outer shell, may be an efficient tool for oxygen release. The aim of this work was to investigate the effects of OLNDs on macrophages functions in hypoxic conditions. In vitro cytotoxicity of OLNDs and their control formulations (dextran oxygen-free nanodroplets, OFNDs) was evaluated by MTT assay and trypan blue staining on monocytes (THP-1 cell line) differentiated into macrophages, after 24 h of incubation in either normoxia (20% O2) or hypoxia (1% O2). The effects of hypoxia on the expression of some genes involved in inflammation were evaluated by quantitative RT-PCR. To establish whether OLNDs are able to modulate the macrophage-mediated inflammatory response in hypoxic conditions, the secretion of different cytokines was evaluated by ELISA assay. OLNDs effects on killing capability, after phagocytosis of Enterococcus faecalis (E. faecalis), was also investigated. Dextran-shelled nanodroplets did not affect viability and killing capability of differentiated THP-1 both in normoxia and hypoxia up to 10% concentration. The expression of some genes coding for cytokines or chemokines, such as CCL2, CXCL6, CXCL8, MIF and TNFalpha, was significantly (p<0.05) increased by hypoxia. TNF-alpha and IL-1beta protein secretion was unaffected by hypoxia, but increased by phagocytosis of E. faecalis. Both OLNDs and OFNDs were able to inhibit TNF-alpha and IL-1beta production induced by E. faecalis, suggesting an anti-inflammatory activity of the dextran shell. This study suggests OLNDs as new and safe potential tools for modulating macrophage functions during hypoxia in chronic wounds.