Modulating Lipid-Polymer Nanoparticles' Physicochemical Properties to Alter Macrophage Uptake

Macrophage uptake of nanoparticles is highly dependent on the physicochemical characteristics of those nanoparticles. Here, we have created a collection of lipid-polymer nanoparticles (LPNPs) varying in size, stiffness, and lipid makeup to determine the effects of these factors on uptake in murine bone marrow-derived macrophages. The LPNPs varied in diameter from 232 to 812 nm, in storage modulus from 21.2 to 287 kPa, and in phosphatidylserine content from 0 to 20%. Stiff, large nanoparticles with a coating containing phosphatidylserine were taken up by macrophages to a much higher degree than any other formulation (between 9.3× and 166× higher than other LPNPs). LPNPs with phosphatidylserine were taken up most by M2-polarized macrophages, while those without were taken up most by M1-polarized macrophages. Differences in total LPNP uptake were not dependent on endocytosis pathway(s) other than phagocytosis. This work acts as a basis for understanding how the interactions between nanoparticle physicochemical characteristics may act synergistically to facilitate particle uptake.

Hydrogel foam dressings with angiogenic and immunomodulatory factors from mesenchymal stem cells

Stem cell therapy and skin substitutes address the stalled healing of chronic wounds in order to promote wound closure; however, the high cost and regulatory hurdles of these treatments limit patient access. A low-cost method to induce bioactive healing has the potential to substantially improve patient care and prevent wound-induced limb loss. A previous study reported that bioactive factors derived from apoptotic-like mesenchymal stem cells (MSCs) demonstrated anti-inflammatory and proangiogenic effects and improved ischemic muscle regeneration. In this work, these MSC-derived bioactive factors were loaded into a hydrogel foam to harness immunomodulatory and angiogenic properties from MSC components to facilitate chronic wound healing without the high cost and translational challenges of cell therapies. After incorporation of bioactive factors, the hydrogel foam retained high absorbency, moisture retention, and target water vapor transmission rate. High loading efficiency was confirmed and release studies indicated that over 90% of loaded factors were released within 24 h. Ethylene oxide sterilization and 4-week storage did not affect the bioactive factor release profile or physical properties of the hydrogel foam dressing. Bioactivity retention of the released factors was also confirmed for as-sterilized, 4°C-stored, and -20°C-stored bioactive hydrogel foams as determined by relevant gene expression levels in treated pro-inflammatory (M1) macrophages. These results support the use of the bioactive dressings as an off-the-shelf product. Overall, this work reports a new method to achieve a first-line wound dressing with the potential to reduce persistent inflammation and promote angiogenesis in chronic wounds.

Soluble components from mesenchymal stromal cell processing exert anti-inflammatory effects and facilitate ischemic muscle regeneration

BACKGROUND AIMS

Skeletal muscle regeneration after severe damage is reliant on local stem cell proliferation and differentiation, processes that are tightly regulated by macrophages. Peripheral artery disease is a globally prevalent cardiovascular disease affecting millions of people. Progression of the disease leads to intermittent claudication, subsequent critical limb ischemia and muscle injury. Tissue-derived and ex vivo-expanded mesenchymal stromal cells (MSCs) for skeletal muscle regeneration have been studied, but pre-clinical and clinical results have not been consistent. As a result, the potential therapeutic efficacy and associated repair mechanisms of MSCs remain unclear. Numerous studies have demonstrated the vulnerability of delivered MSCs, with a precipitous drop in cell viability upon transplantation. This has prompted investigation into the therapeutic benefit of apoptotic cells, microvesicles, exosomes and soluble signals that are released upon cell death.

METHODS

In this study, we characterized various components produced by MSCs after cell death induction under different conditions. We discovered anti-inflammatory and pro-regenerative effects produced by cell components following a freeze and thaw (F&T) process on macrophage polarization in vitro. We further investigated the underlying mechanisms of macrophage polarization by those components resulting from severe cell death induction.

RESULTS

We found potent therapeutic effects from F&T-induced cell debris are dependent on the externalization of phosphatidylserine on the plasma membrane. In contrast, effects from the supernatant of F&T-induced cell death primarily depends on the released protein content. We then applied the F&T-induced cell supernatant to an animal model of peripheral artery disease to treat muscle injury caused by severe ischemia. Treatment with the F&T supernatant but not the vulnerable MSCs resulted in significantly improved recovery of muscle function, blood flow and morphology and inflammation resolution in the affected muscles 2 weeks after injury.

CONCLUSIONS

This study validates the therapeutic potential of F&T-induced supernatant obviating the need for a viable population from vulnerable MSCs to treat injury, thus providing a roadmap for cell-free therapeutic approaches for tissue regeneration.

Apoptotic body-inspired nanoparticles target macrophages at sites of inflammation to support an anti-inflammatory phenotype shift

Chronic inflammation is a significant pathological process found in a range of disease states. Treatments to reduce inflammation in this family of diseases may improve symptoms and disease progression, but are largely limited by variable response rates, cost, and off-target effects. Macrophages are implicated in many inflammatory diseases for their critical role in the maintenance and resolution of inflammation. Macrophages exhibit significant plasticity to direct the inflammatory response by taking on an array of pro- and anti-inflammatory phenotypes based on extracellular cues. In this work, a nanoparticle has been developed to target sites of inflammation and reduce the inflammatory macrophage phenotype by mimicking the anti-inflammatory effect of apoptotic cell engulfment. The nanoparticle, comprised of a poly(lactide-co-glycolide) core, is coated with phosphatidylserine (PS)-supplemented cell plasma membrane to emulate key characteristics of the apoptotic cell surface. T he particle surface is additionally functionalized with an acid-sensitive sheddable polyethylene glycol (PEG) moiety to increase the delivery of the nanoparticles to low pH environments such as those of chronic inflammation. In a mouse model of lipopolysaccharide-induced inflammation, particles were preferentially taken up by macrophages at the site and promoted an anti-inflammatory phenotype shift. This PEGylated membrane coating increased the delivery of nanoparticles to sites of inflammation and may be used as a tool alone or as a delivery scheme for additional cargo to reduce macrophage-associated inflammatory response.

Cell-Inspired Biomaterials for Modulating Inflammation

Inflammation is a crucial part of wound healing and pathogen clearance. However, it can also play a role in exacerbating chronic diseases and cancer progression when not regulated properly. A subset of current innate immune engineering research is focused on how molecules such as lipids, proteins, and nucleic acids native to a healthy inflammatory response can be harnessed in the context of biomaterial design to promote healing, decrease disease severity, and prolong survival. The engineered biomaterials in this review inhibit inflammation by releasing anti-inflammatory cytokines, sequestering proinflammatory cytokines, and promoting phenotype switching of macrophages in chronic inflammatory disease models. Conversely, other biomaterials discussed here promote inflammation by mimicking pathogen invasion to inhibit tumor growth in cancer models. The form that these biomaterials take spans a spectrum from nanoparticles to large-scale hydrogels to surface coatings on medical devices. Cell-inspired molecules have been incorporated in a variety of creative ways, including loaded into or onto the surface of biomaterials or used as the biomaterials themselves.