Ultrasound-activated decafluoropentane/chitosan nanodroplets effectively release oxygen to the skin.

Perfluoropentane (PFP)-based oxygen-loaded nanobubbles (OLNBs) were previously proposed as adjuvant therapeutic tools for pathologies of different etiology sharing hypoxia as a common feature, including cancer, infection, and autoimmunity. Here we introduce a new platform of oxygen nanocarriers, based on 2H,3H-decafluoropentane (DFP) as core fluorocarbon. These new nanocarriers have been named oxygen-loaded nanodroplets (OLNDs) since DFP is liquid at body temperature, unlike gaseous PFP. Dextran-shelled OLNDs, available either in liquid or gel formulations, display spherical morphology, ~600 nm diameters, anionic charge, good oxygen carrying capacity, and no toxic effects on human keratinocytes after cell internalization. In vitro OLNDs result more effective in releasing oxygen to hypoxic environments than former OLNBs, as demonstrated by analysis through oxymetry. In vivo, OLNDs effectively enhance oxy-hemoglobin levels, as emerged from investigation by photoacoustic imaging. Interestingly, ultrasound (US) treatment further improves transdermal oxygen release from OLNDs. Taken together, these data suggest that US-activated, DFP-based OLNDs might be innovative, suitable and cost-effective devices to topically treat hypoxia-associated pathologies of the cutaneous tissues.

When citing, please refer to the published version. MMP-9 and increases TIMP-1 without affecting TIMP-2 secretion, whereas in human 60 keratinocytes it reduces MMP-2, MMP-9, and TIMP-2, without affecting TIMP-1 release. 61Provided that the phenotype of the cellular environment is better understood, chronic wounds 62 might be targeted by new oxygenating compounds such as chitosan-or dextran-shelled and 63 2H,3H-decafluoropentane-cored oxygen-loaded nanodroplets (OLNs). Here, we investigated 64 the effects of hypoxia and dextran-shelled OLNs on the pro-angiogenic phenotype and 65 behavior of human dermal microvascular endothelium (HMEC-1 cell line), another cell 66 population playing key roles during wound healing. Normoxic HMEC-1 constitutively 67 released MMP-2, TIMP-1 and TIMP-2 proteins, but not MMP-9. Hypoxia enhanced MMP-2 68 and reduced TIMP-1 secretion, without affecting TIMP-2 levels, and compromised cell 69 ability to migrate and invade the extracellular matrix. When taken up by HMEC-1, nontoxic 70OLNs abrogated the effects of hypoxia, restoring normoxic MMP/TIMP levels and 71 promoting cell migration, matrix invasion, and formation of microvessels. These effects were 72 specifically dependent on time-sustained oxygen diffusion from OLN core, since they were 73 not achieved by oxygen-free nanodroplets or oxygen-saturated solution. Collectively, these 74 data provide new information on the effects of hypoxia on dermal endothelium and support 75 the hypothesis that OLNs might be used as effective adjuvant tools to promote chronic wound 76 healing processes. 77 78Keywords: oxygen; nanodroplet; matrix metalloproteinase (MMP); tissue inhibitor of 79 metalloproteinase (TIMP); human microvascular endothelial cell (HMEC); skin. 80 5 Introduction 81 82After injury, skin integrity must be restored promptly to reestablish the homeostatic 83 mechanisms, minimize fluid loss, and prevent infection [Greaves et al., 2013]. This is 84 achieved through wound healing, a complex biological process where multiple pathways are 85 simultaneously activated to induce tissue repair and regeneration. Traditionally, acute wound 86 healing is defined as a complex multi-step and multi-cellular process, distinguished in four 87 phases involving different cell types: i) hemostasis, involving platelets; ii) inflammation, 88 involving neutrophils, monocytes, and macrophages; iii) proliferation, involving 89 keratinocytes, endothelial cells, and fibroblasts; and iv) matrix remodeling, involving 90 keratinocytes, myofibroblasts, and endothelial cells. [Diegelmann et al., 2004]. In particular, 91 during the third and fourth phases, the endothelium plays a pivotal role, since wound 92 microvasculature is rebuilt through angiogenesis to restore the supply of oxygen, blood 93 constituents and nutrients to the regenerating tissue, helping to promote fibroplasia and 94 prevent sustained tissue hypoxia [Eming et al., 2014]. Notably, oxygen represents a key 95 regulator of normal wound healing since it is required for collagen deposition, 96 epith...

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Monocytes play a key role in the inflammatory stage of the healing process. To allow monocyte migration to injured tissues, the balances between secreted matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) must be finely modulated. However, a reduction of blood supply and local oxygen tension can modify the phenotype of immune cells. Intriguingly, hypoxia might be targeted by new effective oxygenating devices such as 2H,3H-decafluoropentane- (DFP-) based oxygen-loaded nanodroplets (OLNs). Here, hypoxia effects on gelatinase/TIMP release from human peripheral monocytes were investigated, and the therapeutic potential of dextran-shelled OLNs was evaluated. Normoxic monocytes constitutively released ~500 ng/mL MMP-9, ~1.3 ng/mL TIMP-1, and ~0.6 ng/mL TIMP-2 proteins. MMP-2 was not detected. After 24 hours, hypoxia significantly altered MMP-9/TIMP-1 balance by reducing MMP-9 and increasing TIMP-1, without affecting TIMP-2 secretion. Interestingly OLNs, not displaying toxicity to human monocytes after cell internalization, effectively counteracted hypoxia, restoring a normoxia-like MMP-9/TIMP-1 ratio. The action of OLNs was specifically dependent on time-sustained oxygen diffusion up to 24 h from their DFP-based core. Therefore, OLNs appear as innovative, nonconventional, cost-effective, and nontoxic therapeutic tools, to be potentially employed to restore the physiological invasive phenotype of immune cells in hypoxia-associated inflammation.

As such, US-activated chitosan-shelled OLNs appear as promising, nonconventional and innovative tools for adjuvant treatment of infected chronic wounds.

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