Macrophage dysfunction impairs resolution of inflammation in the wounds of diabetic mice

Impact of resolvin E1 on murine neutrophil phagocytosis in type 2 diabetes

Diabetic complications involve inflammation-mediated microvascular and macrovascular damage, disruption of lipid metabolism, glycosylation of proteins, and abnormalities of neutrophil-mediated events. Resolution of inflamed tissues to health and homeostasis is an active process mediated by endogenous lipid agonists, including lipoxins and resolvins. This proresolution system appears to be compromised in type 2 diabetes (T2D). The goal of this study was to investigate unresolved inflammation in T2D. Wild-type (WT) and genetically engineered mice, including T2D mice (db/db), transgenic mice overexpressing the human resolvin E1 (RvE1) receptor (ERV1), and a newly bred strain of db/ERV1 mice, were used to determine the impact of RvE1 on the phagocytosis of Porphyromonas gingivalis in T2D. Neutrophils were isolated and incubated with fluorescein isothiocyanate-labeled P. gingivalis, and phagocytosis was measured in a fluorochrome-based assay by flow cytometry. Mitogen-activated protein kinase (MAPK) (p42 and p44) and Akt (Thr308 and Ser473) phosphorylation was analyzed by Western blotting. The mouse dorsal air pouch model was used to evaluate the in vivo impact of RvE1. Results revealed that RvE1 increased the neutrophil phagocytosis of P. gingivalis in WT animals but had no impact in db/db animals. In ERV1-transgenic and ERV1-transgenic diabetic mice, phagocytosis was significantly increased. RvE1 decreased Akt and MAPK phosphorylation in the transgenic animals. In vivo dorsal air pouch studies revealed that RvE1 decreases neutrophil influx into the pouch and increases neutrophil phagocytosis of P. gingivalis in the transgenic animals; cutaneous fat deposition was reduced, as was macrophage infiltration. The results suggest that RvE1 rescues impaired neutrophil phagocytosis in obese T2D mice overexpressing ERV1.

Palatogenesis and cutaneous repair: A two-headed coin

BACKGROUND

The reparative mechanism that operates following post-natal cutaneous injury is a fundamental survival function that requires a well-orchestrated series of molecular and cellular events. At the end, the body will have closed the hole using processes like cellular proliferation, migration, differentiation and fusion.

RESULTS

These processes are similar to those occurring during embryogenesis and tissue morphogenesis. Palatogenesis, the formation of the palate from two independent palatal shelves growing towards each other and fusing, intuitively, shares many similarities with the closure of a cutaneous wound from the two migrating epithelial fronts.

CONCLUSIONS

In this review, we summarize the current information on cutaneous development, wound healing, palatogenesis and orofacial clefting and propose that orofacial clefting and wound healing are conserved processes that share common pathways and gene regulatory networks.

Rethinking regenerative medicine: a macrophage-centered approach

Regenerative medicine, a multi-disciplinary approach that seeks to restore form and function to damaged or diseased tissues and organs, has evolved significantly during the past decade. By adapting and integrating fundamental knowledge from cell biology, polymer science, and engineering, coupled with an increasing understanding of the mechanisms which underlie the pathogenesis of specific diseases, regenerative medicine has the potential for innovative and transformative therapies for heretofore unmet medical needs. However, the translation of novel technologies from the benchtop to animal models and clinical settings is non-trivial and requires an understanding of the mechanisms by which the host will respond to these novel therapeutic approaches. The role of the innate immune system, especially the role of macrophages, in the host response to regenerative medicine based strategies has recently received considerable attention. Macrophage phenotype and function have been suggested as critical and determinant factors in downstream outcomes. The constructive and regulatory, and in fact essential, role of macrophages in positive outcomes represents a significant departure from the classical paradigms of host-biomaterial interactions, which typically consider activation of the host immune system as a detrimental event. It appears desirable that emerging regenerative medicine approaches should not only accommodate but also promote the involvement of the immune system to facilitate positive outcomes. Herein, we describe the current understanding of macrophage phenotype as it pertains to regenerative medicine and suggest that improvement of our understanding of context-dependent macrophage polarization will lead to concurrent improvement in outcomes.

A modified collagen gel dressing promotes angiogenesis in a preclinical swine model of chronic ischemic wounds

We recently performed proteomic characterization of a modified collagen gel (MCG) dressing and reported promising effects of the gel in healing full-thickness excisional wounds. In this work, we test the translational relevance of our aforesaid findings by testing the dressing in a swine model of chronic ischemic wounds recently reported by our laboratory. Full-thickness excisional wounds were established in the center of bipedicle ischemic skin flaps on the backs of animals. Ischemia was verified by laser Doppler imaging, and MCG was applied to the test group of wounds. Seven days post wounding, macrophage recruitment to the wound was significantly higher in MCG-treated ischemic wounds. In vitro, MCG up-regulated expression of Mrc-1 (a reparative M2 macrophage marker) and induced the expression of anti-inflammatory cytokine interleukin (IL)-10 and of fibroblast growth factor-basic (β-FGF). An increased expression of CCR2, an M2 macrophage marker, was noted in the macrophages from MCG treated wounds. Furthermore, analyses of wound tissues 7 days post wounding showed up-regulation of transforming growth factor-β, vascular endothelial growth factor, von Willebrand's factor, and collagen type I expression in MCG-treated ischemic wounds. At 21 days post wounding, MCG-treated ischemic wounds displayed higher abundance of proliferating endothelial cells that formed mature vascular structures and increased blood flow to the wound. Fibroblast count was markedly higher in MCG-treated ischemic wound-edge tissue. In addition, MCG-treated wound-edge tissues displayed higher abundance of mature collagen with increased collagen type I : III deposition. Taken together, MCG helped mount a more robust inflammatory response that resolved in a timely manner, followed by an enhanced proliferative phase, angiogenic outcome, and postwound tissue remodeling. Findings of the current study warrant clinical testing of MCG in a setting of ischemic chronic wounds.

Activated macrophages create lineage-specific microenvironments for pancreatic acinar- and β-cell regeneration in mice

BACKGROUND & AIMS

Although the cells that contribute to pancreatic regeneration have been widely studied, little is known about the mediators of this process. During tissue regeneration, infiltrating macrophages debride the site of injury and coordinate the repair response. We investigated the role of macrophages in pancreatic regeneration in mice.

METHODS

We used a saporin-conjugated antibody against CD11b to reduce the number of macrophages in mice following diphtheria toxin receptor-mediated cell ablation of pancreatic cells, and evaluated the effects on pancreatic regeneration. We analyzed expression patterns of infiltrating macrophages after cell-specific injury or from the pancreas of nonobese diabetic mice. We developed an in vitro culture system to study the ability of macrophages to induce cell-specific regeneration.

RESULTS

Depletion of macrophages impaired pancreatic regeneration. Macrophage polarization, as assessed by expression of tumor necrosis factor-α, interleukin 6, interleukin 10, and CD206, depended on the type of injury. The signals provided by polarized macrophages promoted lineage-specific generation of acinar or endocrine cells. Macrophage from nonobese diabetic mice failed to provide signals necessary for β-cell generation.

CONCLUSIONS

Macrophages produce cell type-specific signals required for pancreatic regeneration in mice. Additional study of these processes and signals might lead to new approaches for treating type 1 diabetes or pancreatitis.

Efficacy of short novel antimicrobial and anti-inflammatory peptides in a mouse model of methicillin-resistant Staphylococcus aureus (MRSA) skin infection

The therapeutic efficacy of two novel short antimicrobial and anti-inflammatory peptides (RR and RRIKA) was evaluated in a mouse model of staphylococcal skin infection. RR (2%) and RRIKA (2%) significantly reduced the bacterial counts and the levels of proinflammatory cytokines, tumor necrosis factor (TNF)-α, and interleukin (IL)-6, in methicillin-resistant Staphylococcus aureus USA 300-0114 skin lesions. Furthermore, the combined therapy of RRIKA (1%) and lysostaphin (0.5%) had significantly higher antistaphylococcal and anti-inflammatory activity compared to monotherapy. This study supports the potential use of these peptides for topical treatment of methicillin-resistant Staphylococcus aureus skin infections.

Comparison of cryopreserved amniotic membrane and umbilical cord tissue with dehydrated amniotic membrane/chorion tissue

OBJECTIVE

To evaluate how the different processing methods cryopreservation and dehydration affect the structural integrity and biological composition of key signalling molecules within amniotic membrane and umbilical cord tissues.

METHOD

We directly compared cryopreserved amniotic membrane (AM) and umbilical cord (UC) tissues with dehydrated amniotic membrane/chorion (dHACM) tissue using biochemical and functional assays including histological and histochemical staining, BCA, agarose gel electrophoresis, western blot, ELISA, and proliferation and cell death assays.

RESULTS

Cryopreservation retains the native architecture of the AM/UC extracellular matrix and maintains the quantity and activity of key biological signals present in fresh AM/UC, including high molecular weight hyaluronic acid, heavy chain-HA complex, and pentraxin 3. In contrast, dehydrated tissues were structurally compromised and almost completely lacked these crucial components.

CONCLUSION

The results presented here indicate that cryopreservation better preserves the structural and biological signaling molecules of foetal tissues.

Neuroprotectin/protectin D1: endogenous biosynthesis and actions on diabetic macrophages in promoting wound healing and innervation impaired by diabetes

Dysfunction of macrophages (MΦs) in diabetic wounds impairs the healing. MΦs produce anti-inflammatory and pro-resolving neuroprotectin/protectin D1 (NPD1/PD1, 10R,17S-dihydroxy-docosa-4Z,7Z,11E,13E,15Z,19Z-hexaenoic acid); however, little is known about endogenous NPD1 biosynthesis by MΦs and the actions of NPD1 on diabetic MΦ functions in diabetic wound healing. We used an excisional skin wound model of diabetic mice, MΦ depletion, MΦs isolated from diabetic mice, and mass spectrometry-based targeted lipidomics to study the time course progression of NPD1 levels in wounds, the roles of MΦs in NPD1 biosynthesis, and NPD1 action on diabetic MΦ inflammatory activities. We also investigated the healing, innervation, chronic inflammation, and oxidative stress in diabetic wounds treated with NPD1 or NPD1-modulated MΦs from diabetic mice. Injury induced endogenous NPD1 biosynthesis in wounds, but diabetes impeded NPD1 formation. NPD1 was mainly produced by MΦs. NPD1 enhanced wound healing and innervation in diabetic mice and promoted MΦs functions that accelerated these processes. The underlying mechanisms for these actions of NPD1 or NPD1-modulated MΦs involved 1) attenuating MΦ inflammatory activities and chronic inflammation and oxidative stress after acute inflammation in diabetic wound, and 2) increasing MΦ production of IL10 and hepatocyte growth factor. Taken together, NPD1 appears to be a MΦs-produced factor that accelerates diabetic wound healing and promotes MΦ pro-healing functions in diabetic wounds. Decreased NPD1 production in diabetic wound is associated with impaired healing. This study identifies a new molecular target that might be useful in development of more effective therapeutics based on NPD1 and syngeneic diabetic MΦs for treatment of diabetic wounds.

Vascular Endothelial Growth Factor and Angiogenesis in the Regulation of Cutaneous Wound Repair

Significance: Angiogenesis, the growth of new blood vessels from existing vessels, is an important aspect of the repair process. Restoration of blood flow to damaged tissues provides oxygen and nutrients required to support the growth and function of reparative cells. Vascular endothelial growth factor (VEGF) is one of the most potent proangiogenic growth factors in the skin, and the amount of VEGF present in a wound can significantly impact healing. Recent Advances: The activity of VEGF was once considered to be specific for endothelial cells lining the inside of blood vessels, partly because VEGF receptor (VEGFR) expression was believed to be restricted to endothelial cells. It is now known, however, that VEGFRs can be expressed by a variety of other cell types involved in wound repair. For example, keratinocytes and macrophages, which both carry out important functions during wound healing, express VEGFRs and are capable of responding directly to VEGF. Critical Issues: The mechanisms by which VEGF promotes angiogenesis are well established. Recent studies, however, indicate that VEGF can directly affect the activity of several nonendothelial cell types present in the skin. The implications of these extra-angiogenic effects of VEGF on wound repair are not yet known, but they suggest that this growth factor may play a more complex role during wound healing than previously believed. Future Directions: Despite the large number of studies focusing on VEGF and wound healing, it is clear that the current knowledge of how VEGF contributes to the repair of skin wounds is incomplete. Further research is needed to obtain a more comprehensive understanding of VEGF activities during the wound healing process.

Maresin-like lipid mediators are produced by leukocytes and platelets and rescue reparative function of diabetes-impaired macrophages

Nonhealing diabetic wounds are associated with impaired macrophage (Mf) function. Leukocytes and platelets (PLT) play crucial roles in wound healing by poorly understood mechanisms. Here we report the identification and characterization of the maresin-like(L) mediators 14,22-dihydroxy-docosa-4Z,7Z,10Z,12E,16Z,19Z-hexaenoic acids, 14S,22-diHDHA (maresin-L1), and 14R,22-diHDHA (maresin-L2) that are produced by leukocytes and PLT and involved in wound healing. We show that 12-lipoxygenase-initiated 14S-hydroxylation or cytochrome P450 catalyzed 14R-hydroxylation and P450-initiated ω(22)-hydroxylation are required for maresin-L biosynthesis. Maresin-L treatment restores reparative functions of diabetic Mfs, suggesting that maresin-Ls act as autocrine/paracrine factors responsible for, at least in part, the reparative functions of leukocytes and PLT in wounds. Additionally, maresin-L ameliorates Mf inflammatory activation and has the potential to suppress the chronic inflammation in diabetic wounds caused by activation of Mfs. These findings provide initial insights into maresin-L biosynthesis and mechanism of action and potentially offer a therapeutic option for better treatment of diabetic wounds.

Wound administration of M2-polarized macrophages does not improve murine cutaneous healing responses

Macrophages play a crucial role in all stages of cutaneous wound healing responses and dysregulation of macrophage function can result in derailed wound repair. The phenotype of macrophages is influenced by the wound microenvironment and evolves during healing from a more pro-inflammatory (M1) profile in early stages, to a less inflammatory pro-healing (M2) phenotype in later stages of repair. The aim of the current study was to investigate the potential of exogenous administration of M2 macrophages to promote wound healing in an experimental mouse model of cutaneous injury. Bone marrow derived macrophages were stimulated in-vitro with IL-4 or IL-10 to obtain two different subsets of M2-polarized cells, M2a or M2c respectively. Polarized macrophages were injected into full-thickness excisional skin wounds of either C57BL/6 or diabetic db/db mice. Control groups were injected with non-polarized (M0) macrophages or saline. Our data indicate that despite M2 macrophages exhibit an anti-inflammatory phenotype in-vitro, they do not improve wound closure in wild type mice while they delay healing in diabetic mice. Examination of wounds on day 15 post-injury indicated delayed re-epithelialization and persistence of neutrophils in M2 macrophage treated diabetic wounds. Therefore, topical application of ex-vivo generated M2 macrophages is not beneficial and contraindicated for cell therapy of skin wounds.

Reduction of ARNT in myeloid cells causes immune suppression and delayed wound healing

Aryl hydrocarbon receptor nuclear translocator (ARNT) is a transcription factor that binds to partners to mediate responses to environmental signals. To investigate its role in the innate immune system, floxed ARNT mice were bred with lysozyme M-Cre recombinase animals to generate lysozyme M-ARNT (LAR) mice with reduced ARNT expression. Myeloid cells of LAR mice had altered mRNA expression and delayed wound healing. Interestingly, when the animals were rendered diabetic, the difference in wound healing between the LAR mice and their littermate controls was no longer present, suggesting that decreased myeloid cell ARNT function may be an important factor in impaired wound healing in diabetes. Deferoxamine (DFO) improves wound healing by increasing hypoxia-inducible factors, which require ARNT for function. DFO was not effective in wounds of LAR mice, again suggesting that myeloid cells are important for normal wound healing and for the full benefit of DFO. These findings suggest that myeloid ARNT is important for immune function and wound healing. Increasing ARNT and, more specifically, myeloid ARNT may be a therapeutic strategy to improve wound healing.

Lysosomes integrate metabolic-inflammatory cross-talk in primary macrophage inflammasome activation

Macrophage dysfunction and inflammasome activation have been implicated in the pathogenesis of diabetes and its complications. Prolonged inflammation and impaired healing are hallmarks of the diabetic response to tissue injury, and excessive inflammasome activation has been associated in these phenotypes. However, the mechanisms that regulate the inflammasome in response to lipid metabolic and inflammatory stress are incompletely understood. We have shown previously that IL-1β secretion is induced in primary macrophages exposed to the dietary saturated fatty acid palmitate in combination with LPS. In this study, we sought to unravel the mechanisms underlying the activation of this lipotoxic inflammasome. We demonstrate that palmitate-loaded primary macrophages challenged with LPS activate the NLRP3 inflammasome through a mechanism that involves the lysosome. Interestingly, the lysosome was involved in both the regulation of pro-IL-1β levels and its subsequent cleavage/release. The lysosomal protease cathepsin B was required for IL-1β release but not pro-IL-1β production. In contrast, disrupting lysosomal calcium regulation decreased IL-1β release by reducing pro-IL-1β levels. The calcium pathway involved the calcium-activated phosphatase calcineurin, which stabilized IL-1β mRNA. Our findings provide evidence that the lysosome plays a key role in both the priming and assembly phases of the lipostoxic inflammasome. These findings have potential relevance to the hyperinflammatory phenotypes observed in diabetics during tissue damage or infection and identify lysosomes and calcineurin as potential therapeutic targets.

Computational approach to characterize causative factors and molecular indicators of chronic wound inflammation

Chronic inflammation is rapidly becoming recognized as a key contributor to numerous pathologies. Despite detailed investigations, understanding of the molecular mechanisms regulating inflammation is incomplete. Knowledge of such critical regulatory processes and informative indicators of chronic inflammation is necessary for efficacious therapeutic interventions and diagnostic support to clinicians. We used a computational modeling approach to elucidate the critical factors responsible for chronic inflammation and to identify robust molecular indicators of chronic inflammatory conditions. Our kinetic model successfully captured experimentally observed cell and cytokine dynamics for both acute and chronic inflammatory responses. Using sensitivity analysis, we identified macrophage influx and efflux rate modulation as the strongest inducing factor of chronic inflammation for a wide range of scenarios. Moreover, our model predicted that, among all major inflammatory mediators, IL-6, TGF-β, and PDGF may generally be considered the most sensitive and robust indicators of chronic inflammation, which is supported by existing, but limited, experimental evidence.

Resolvins, specialized proresolving lipid mediators, and their potential roles in metabolic diseases

Inflammation is associated with the development of diseases characterized by altered nutrient metabolism. Although an acute inflammatory response is host-protective and normally self-limited, chronic low-grade inflammation associated with metabolic diseases is sustained and detrimental. The resolution of inflammation involves the termination of neutrophil recruitment, counterregulation of proinflammatory mediators, stimulation of macrophage-mediated clearance, and tissue remodeling. Specialized proresolving lipid mediators (SPMs)-resolvins, protectins, and maresins-are novel autacoids that resolve inflammation, protect organs, and stimulate tissue regeneration. Here, we review evidence that the failure of resolution programs contributes to metabolic diseases and that SPMs may play pivotal roles in their resolution.

Engulfment of apoptotic cells by macrophages: a role of microRNA-21 in the resolution of wound inflammation

At an injury site, efficient clearance of apoptotic cells by wound macrophages or efferocytosis is a prerequisite for the timely resolution of inflammation. Emerging evidence indicates that microRNA-21 (miR-21) may regulate the inflammatory response. In this work, we sought to elucidate the significance of miR-21 in the regulation of efferocytosis-mediated suppression of innate immune response, a key process implicated in resolving inflammation following injury. An increased expression of inducible miR-21 was noted in postefferocytotic peripheral blood monocyte-derived macrophages. Such induction of miR-21 was associated with silencing of its target genes PTEN and PDCD4. Successful efferocytosis of apoptotic cells by monocyte-derived macrophages resulted in the suppression of LPS-induced NF-κB activation and TNF-α expression. Interestingly, bolstering of miR-21 levels alone, using miR mimic, resulted in significant suppression of LPS-induced TNF-α expression and NF-κB activation. We report that efferocytosis-induced miR-21, by silencing PTEN and GSK3β, tempers the LPS-induced inflammatory response. Macrophage efferocytosis is known to trigger the release of anti-inflammatory cytokine IL-10. This study demonstrates that following successful efferocytosis, miR-21 induction in macrophages silences PDCD4, favoring c-Jun-AP-1 activity, which in turn results in elevated production of anti-inflammatory IL-10. In summary, this work provides direct evidence implicating miRNA in the process of turning on an anti-inflammatory phenotype in the postefferocytotic macrophage. Elevated macrophage miR-21 promotes efferocytosis and silences target genes PTEN and PDCD4, which in turn accounts for a net anti-inflammatory phenotype. Findings of this study highlight the significance of miRs in the resolution of wound inflammation.

Generating and reversing chronic wounds in diabetic mice by manipulating wound redox parameters

By 2025, more than 500 M people worldwide will suffer from diabetes; 125 M will develop foot ulcer(s) and 20 M will undergo an amputation, creating a major health problem. Understanding how these wounds become chronic will provide insights to reverse chronicity. We hypothesized that oxidative stress (OS) in wounds is a critical component for generation of chronicity. We used the db/db mouse model of impaired healing and inhibited, at time of injury, two major antioxidant enzymes, catalase and glutathione peroxidase, creating high OS in the wounds. This was necessary and sufficient to trigger wounds to become chronic. The wounds initially contained a polymicrobial community that with time selected for specific biofilm-forming bacteria. To reverse chronicity we treated the wounds with the antioxidants α-tocopherol and N-acetylcysteine and found that OS was highly reduced, biofilms had increased sensitivity to antibiotics, and granulation tissue was formed with proper collagen deposition and remodeling. We show for the first time generation of chronic wounds in which biofilm develops spontaneously, illustrating importance of early and continued redox imbalance coupled with the presence of biofilm in development of wound chronicity. This model will help decipher additional mechanisms and potentially better diagnosis of chronicity and treatment of human chronic wounds.

Continuous electrical current and zinc sulphate administered by transdermal iontophoresis improves skin healing in diabetic rats induced by alloxan: morphological and ultrastructural analysis

PURPOSE

Evaluated the effects of continuous electrical current (CEC) or zinc administrated by transdermal iontophoresis (Zn+TDI).

METHODS

120 male Wistar rats were submitted to an incision surgery at the anterior region of abdomen and distributed into 6 experimental groups with 40 animals: 3 diabetic groups and 3 normal groups, untreated and treated with CEC alone or with Zn + TDI. Each group was further divided into 4 subgroups with 10 rats each to be evaluated on the 4th, 7th, 14th, and 21st day after surgery. In each period, clinical and laboratory parameters from the animals were analyzed.

RESULTS

The analysis by optical and scanning electron microscopy showed a delay in the phases of wound healing in diabetic rats without treatment in all periods of the experiment; breaking strength (BS) was significantly reduced in skin scars of untreated diabetic rats when compared to other groups. In contrast, BS in skin scars of nondiabetic groups and diabetic rats treated with Zn + TDI showed significant increase in those, besides not presenting delayed healing.

CONCLUSION

Electrical stimulation of surgical wounds used alone or in association with zinc by TDI is able to consistently improve the morphological and ultrastructural changes observed in the healing of diabetic animals.

Exercise, Obesity, and Cutaneous Wound Healing: Evidence from Rodent and Human Studies

Significance: Impaired cutaneous wound healing is a major health concern. Obesity has been shown in a number of studies to impair wound healing, and chronic nonhealing wounds in obesity and diabetes are a major cause of limb amputations in the United States. Recent Advances: Recent evidence indicates that aberrant wound site inflammation may be an underlying cause for delayed healing. Obesity, diabetes, and other conditions such as stress and aging can result in a chronic low-level inflammatory state, thereby potentially affecting wound healing negatively. Critical Issues: Interventions which can speed the healing rate in individuals with slowly healing or nonhealing wounds are of critical importance. Recently, physical exercise training has been shown to speed healing in both aged and obese mice and in older adults. Exercise is a relatively low-cost intervention strategy which may be able to be used clinically to prevent or treat impairments in the wound-healing process. Future Directions: Little is known about the mechanisms by which exercise speeds healing. Future translational studies should address potential mechanisms for these exercise effects. Additionally, clinical studies in obese humans are necessary to determine if findings in obese rodent models translate to the human population.

Activity of mesenchymal stem cells in therapies for chronic skin wound healing

Chronic or non-healing skin wounds present an ongoing challenge in advanced wound care, particularly as the number of patients increases while technology aimed at stimulating wound healing in these cases remains inefficient. Mesenchymal stem cells (MSCs) have proved to be an attractive cell type for various cell therapies due to their ability to differentiate into various cell lineages, multiple donor tissue types, and relative resilience in ex-vivo expansion, as well as immunomodulatory effects during transplants. More recently, these cells have been targeted for use in strategies to improve chronic wound healing in patients with diabetic ulcers or other stasis wounds. Here, we outline several mechanisms by which MSCs can improve healing outcomes in these cases, including reducing tissue inflammation, inducing angiogenesis in the wound bed, and reducing scarring following the repair process. Approaches to extend MSC life span in implant sites are also examined.

Use of a fibrin-based system for enhancing angiogenesis and modulating inflammation in the treatment of hyperglycemic wounds

The complex pathophysiology of chronic ulceration in diabetic patients is poorly understood; diabetes-related lower limb amputation is a major health issue, which has limited effective treatment regimes in the clinic. This study attempted to understand the complex pathology of hyperglycemic wound healing by showing profound changes in gene expression profiles in wounded human keratinocytes in hyperglycemic conditions compared to normal glucose conditions. In the hyper-secretory wound microenvironment of hyperglycemia, Rab18, a secretory control molecule, was found to be significantly downregulated. Using a biomaterial platform for dual therapy targeting the two distinct pathways, this study aimed to resolve the major dysregulated pathways in hyperglycemic wound healing. To complement Rab18, and promote angiogenesis eNOS was also targeted, and this novel Rab18-eNOS therapy via a dynamically controlled 'fibrin-in-fibrin' delivery system, demonstrated enhanced wound closure, by increasing functional angiogenesis and reducing inflammation, in an alloxan-induced hyperglycemic preclinical ear ulcer model of compromised wound healing.

Ixmyelocel-T, an expanded multicellular therapy, contains a unique population of M2-like macrophages

INTRODUCTION

M2 macrophages promote tissue repair and regeneration through various mechanisms including immunomodulation and scavenging of tissue debris. Delivering increased numbers of these cells to ischemic tissues may limit tissue injury and promote repair. Ixmyelocel-T is an expanded, autologous multicellular therapy cultured from bone-marrow mononuclear cells (BMMNCs). The purpose of this study was to characterize further a unique expanded population of M2-like macrophages, generated in ixmyelocel-T therapy.

METHODS

Approximately 50 ml of whole bone marrow was obtained from healthy donors and shipped overnight. BMMNCs were produced by using density-gradient separation and cultured for approximately 12 days to generate ixmyelocel-T. CD14+ cells were isolated from ixmyelocel-T with positive selection for analysis. Cell-surface phenotype was examined with flow cytometry and immunofluorescence, and expression of cytokines and chemokines was analyzed with enzyme-linked immunosorbent assay (ELISA). Quantitative real-time PCR was used to analyze expression of genes in BMMNCs, ixmyelocel-T, the CD14+ population from ixmyelocel-T, and M1 and M2 macrophages. Ixmyelocel-T was cultured with apoptotic BMMNCs, and then visualized under fluorescence microscopy to assess efferocytosis.

RESULTS

Macrophages in ixmyelocel-T therapy expressed surface markers of M2 macrophages, CD206, and CD163. These cells were also found to express several M2 markers, and few to no M1 markers. After stimulation with lipopolysaccharide (LPS), they showed minimal secretion of the proinflammatory cytokines interleukin-12 (IL-12) and tumor necrosis factor alpha (TNF-α) compared with M1 and M2 macrophages. Ixmyelocel-T macrophages efficiently ingested apoptotic BMMNCs.

CONCLUSIONS

Ixmyelocel-T therapy contains a unique population of M2-like macrophages that are characterized by expression of M2 markers, decreased secretion of proinflammatory cytokines after inflammatory stimuli, and efficient removal of apoptotic cells. This subpopulation of cells may have a potential role in tissue repair and regeneration.

Insulin treatment modulates the host immune system to enhance Pseudomonas aeruginosa wound biofilms

Diabetes affects 25.8 million people in the United States, or 8.3% of the population, and these numbers are even higher in developing countries. Diabetic patients are more susceptible to the development of chronic wounds with debilitating bacterial infections than nondiabetics. Previously, we compared the ability of the opportunistic pathogen Pseudomonas aeruginosa to cause biofilm-associated infections in chronic wounds of diabetic and nondiabetic mice (C. Watters, K. DeLeon, U. Trivedi, J. A. Griswold, M. Lyte, K. J. Hampel, M. J. Wargo, and K. P. Rumbaugh, Med. Microbiol. Immunol. 202:131-141, 2013). Unexpectedly, we observed that insulin-treated diabetic mice had significantly more biofilm in their wounds, which correlated with higher antibiotic tolerance. Here, we investigated whether insulin treatment modulates the diabetic immune system to favor P. aeruginosa biofilm formation. Utilizing a murine chronic wound model, we found that DNA protected P. aeruginosa in the wounds of insulin-treated diabetic mice from antibiotic treatment. We also observed increased numbers of neutrophils, reduced numbers of macrophages, and increased cell death in the wounds of diabetic mice on insulin therapy. Taken together, these data suggest that high levels of lysed neutrophils in the wounds of diabetic mice on insulin, combined with fewer macrophages to remove the cellular debris, contribute to increased DNA levels, which enhance P. aeruginosa biofilms.

Enhancement of bone regeneration by dual release of a macrophage recruitment agent and platelet-rich plasma from gelatin hydrogels

Macrophages play an important role in regulating inflammatory responses and tissue regeneration. In the present study, their effect on bone remodeling is investigated by the simultaneous application of a macrophage recruiting agent, SEW2871 of a sphingosine-1 phosphate agonist, and platelet-rich plasma (PRP). The non-water soluble SEW2871 was solubilized in water through micelles formation with l-lactic acid grafted gelatin, and the resulting micelles with PRP were incorporated into gelatin hydrogels. Mixed SEW2871-micelles and PRP were released from gelatin hydrogels in a controlled fashion both in vitro and in vivo. In vitro migration assay revealed that the presence of PRP synergistically promoted SEW2871-induced macrophages migration. When applied to a bone defect of rats, the hydrogels incorporating mixed SEW2871-micelles and PRP recruited a higher number of macrophages than those hydrogels incorporating either SEW2871-micelles or PRP. The hydrogels incorporating mixed SEW2871-micelles and PRP enhanced the level of tumor necrosis factor (TNF)-α of pro-inflammatory cytokine, 3 days after application, while pro-inflammatory responses coupled with a significant increase in the expression level of osteoprotegerin (OPG) and interleukin (IL)-10 and transforming growth factor (TGF)-β1 of anti-inflammatory cytokine were observed 10 days postoperatively. The hydrogels incorporating mixed SEW2871-micelles and PRP promoted bone regeneration to a significant great extent compared with those incorporating PBS and either SEW2871-micelles or PRP. It is concluded that macrophages recruitment contributed to PRP-induced bone regeneration.

Effect of activated autologous monocytes/macrophages on wound healing in a rodent model of experimental diabetes

AIM

We aimed to evaluate the effectiveness of the application of activated autologous monocytes/macrophages (Mo/Mp) on wound healing in diabetic rats.

METHODS

Sixty male SD rats were equally divided into the following: control group (normal, nondiabetic), PBS-treated diabetic group, and tumor necrotic factor alpha (TNF-α) plus interferon-γ (IFN-γ)-stimulated or unstimulated Mo/Mp-treated diabetic group. Full-thickness round wounds (1cm×1cm) were created in the right hind foot of rats and the wounds were treated with PBS or Mo/Mp on day 1 after injury. In the following 14 days, the percentage of wound contraction was measured, histologic examination was performed with hematoxylin and eosin staining, and vascular endothelial growth factor (VEGF) in the wound was evaluated by Western blot analysis.

RESULTS

Diabetic rats exhibited impaired wound healing with delayed angiogenesis and VEGF expression. The early application of TNF-α plus IFN-γ-stimulated autologous Mo/Mp to diabetic wounds significantly improved the delayed wound healing through the stimulation of angiogenesis and re-epithelization, as well as restoring the defect in VEGF expression.

CONCLUSIONS

Mo/Mp activated by TNF-α and IFN-γ promotes diabetic wound healing and normalizes the defect in VEGF regulation associated with diabetes-induced skin-repair disorders.

Apoptosis and angiogenesis: an evolving mechanism for fibrosis

Fibrosis, seen in the liver, lung, heart, kidney, and skin, is a significant global disease burden. Currently, therapeutic treatment is limited, and the number of cases continues to grow. Apoptosis has been identified as a potential initiator and propagator of fibrosis. This review specifically examines the correlation between the presence of apoptotic cells and their effect on fibroblast phenotype and collagen metabolism in several different experimental models of fibrosis. Fibrosis in these models is generally preceded by robust angiogenesis and vascular regression, suggesting that the vascular apoptotic burden may be important to fibrotic outcomes. This review considers the emerging evidence that angiogenesis or vascular regression contributes to fibrosis and identifies initial vascular outgrowth or vascular apoptotic cell presence as possible regulators of fibrosis. A further understanding of the cellular mechanisms of fibrosis may suggest novel methods for the reduction of the fibrotic response and promotion of regeneration.

Phenotypic transitions of macrophages orchestrate tissue repair

Macrophages are essential for the efficient healing of numerous tissues, and they contribute to impaired healing and fibrosis. Tissue repair proceeds through overlapping phases of inflammation, proliferation, and remodeling, and macrophages are present throughout this progression. Macrophages exhibit transitions in phenotype and function as tissue repair progresses, although the precise factors regulating these transitions remain poorly defined. In efficiently healing injuries, macrophages present during a given stage of repair appear to orchestrate transition into the next phase and, in turn, can promote debridement of the injury site, cell proliferation and angiogenesis, collagen deposition, and matrix remodeling. However, dysregulated macrophage function can contribute to failure to heal or fibrosis in several pathological situations. This review will address current knowledge of the origins and functions of macrophages during the progression of tissue repair, with emphasis on skin and skeletal muscle. Dysregulation of macrophages in disease states and therapies targeting macrophage activation to promote tissue repair are also discussed.

Neutrophils and Wound Repair: Positive Actions and Negative Reactions

SIGNIFICANCE

Neutrophils are one of the most abundant cells of the immune system and they are extremely active during the repair of cutaneous wounds. In general, the antimicrobial activity of neutrophils is effective and allows these cells to carry out their primary function of preventing wounds from becoming infected.

RECENT ADVANCES

It is now known that in addition to sterilizing the wound, the weapons used by neutrophils to kill potential pathogens can also cause significant tissue damage to the host. This additional damage can lead to delayed healing and excessive scar formation.

CRITICAL ISSUES

Much of the host damage caused by neutrophils results from the activity of proteases secreted by these cells. The clinical significance of this problem is highlighted by numerous studies showing that high levels of neutrophil-derived proteases are associated with chronic, non-healing wounds.

FUTURE DIRECTIONS

Studies are currently being performed to evaluate new ways of counteracting protease activity in chronic wounds. Additional studies will have to be carried out to determine whether neutralizing neutrophil proteases can improve the healing of chronic wounds without sacrificing the ability of neutrophils to eliminate pathogens and risking infection.

Disclosure of the Culprits: Macrophages-Versatile Regulators of Wound Healing

SIGNIFICANCE

Macrophages are invariably present and tightly regulate all phases of adult wound healing, including inflammation, granulation tissue formation, and matrix deposition with the unavoidable outcome of scar formation. In response to environmental cues, macrophages mount a "classical" pro-inflammatory M1 activation as opposed to the "alternative" M2 phenotype, with wound macrophages having long been viewed as M2 macrophages.

RECENT ADVANCES

Recent studies rather point to large temporal and phenotypic variations of wound macrophages subsets. Therefore, a functional classification of macrophages according to wound-healing phases appears to better meet the in vivo complexity. In an ideal but simplistic scenario grossly reflecting normal wound healing, initial tissue injury induces inflammatory M1-like macrophages, which, upon engulfment of apoptotic neutrophils or in response to other inflammation dampening stimuli, switch toward anti-inflammatory M2-like macrophages and further toward growth factor-producing pro-fibrotic M2a-like macrophages. Although not yet documented for skin wounds, a subset of metalloproteinase-producing fibrolytic M2c-like macrophages may contribute to fibrosis resolution. Recent work identified a diversity of novel macrophage phenotypes associated with normal and pathologic wound healing, most of them ranging out of the M1/M2 paradigm. Iron-overloaded M1-like macrophages represent such a novel phenotypic subset driving the non-healing state of chronic venous leg ulcers.

CRITICAL ISSUES

Despite growing evidence that macrophage dysfunctions are, at least in part, responsible for pathologic wound healing, including nonhealing wounds and excessive scar formation, these are hardly specifically addressed even by modern therapeutic strategies.

FUTURE DIRECTIONS

If characterized in sufficient detail, distinct macrophage subsets and their impaired functions provide ideal targets for improving wound healing.

Neurotensin modulates the migratory and inflammatory response of macrophages under hyperglycemic conditions

Diabetic foot ulcers (DFUs) are characterized by an unsatisfactory inflammatory and migratory response. Skin inflammation involves the participation of many cells and particularly macrophages. Macrophage function can be modulated by neuropeptides; however, little is known regarding the role of neurotensin (NT) as a modulator of macrophages under inflammatory and hyperglycemic conditions. RAW 264.7 cells were maintained at 10/30 mM glucose, stimulated with/without LPS (1 μg/mL), and treated with/without NT(10 nM). The results show that NT did not affect macrophage viability. However, NT reverted the hyperglycemia-induced impair in the migration of macrophages. The expression of IL-6 and IL-1β was significantly increased under 10 mM glucose in the presence of NT, while IL-1β and IL-12 expression significantly decreased under inflammatory and hyperglycemic conditions. More importantly, high glucose modulates NT and NT receptor expression under normal and inflammatory conditions. These results highlight the effect of NT on cell migration, which is strongly impaired under hyperglycemic conditions, as well as its effect in decreasing the proinflammatory status of macrophages under hyperglycemic and inflammatory conditions. These findings provide new insights into the potential therapeutic role of NT in chronic wounds, such as in DFU, characterized by a deficit in the migratory properties of cells and a chronic proinflammatory status.

Diabetes impairs adipose tissue-derived stem cell function and efficiency in promoting wound healing

Adipose tissue-derived stem cells (ASCs) are gaining increasing consideration in tissue repair therapeutic application. Recent evidence indicates that ASCs enhance skin repair in animal models of impaired wound healing. To assess the therapeutic activity of autologous vs. allogeneic ASCs in the treatment of diabetic ulcers, we functionally characterized diabetic ASCs and investigated their potential to promote wound healing with respect to nondiabetic ones. Adipose tissue-derived cells from streptozotocin-induced type 1 diabetic mice were analyzed either freshly isolated as stromal vascular fraction (SVF), or following a single passage of culture (ASCs). Diabetic ASCs showed decreased proliferative potential and migration. Expression of surface markers was altered in diabetic SVF and cultured ASCs, with a reduction in stem cell marker-positive cells. ASCs from diabetic mice released lower amounts of hepatocyte growth factor, vascular endothelial growth factor (VEGF)-A, and insulin-like growth factor-1, growth factors playing important roles in skin repair. Accordingly, the supernatant of diabetic ASCs manifested reduced capability to promote keratinocyte and fibroblast proliferation and migration. Therapeutic potential of diabetic SVF administered to wounds of diabetic mice was blunted as compared with cells isolated from nondiabetic mice. Our data indicate that diabetes alters ASC intrinsic properties and impairs their function, thus affecting therapeutic potential in the autologous treatment for diabetic ulcers.

Enhanced lymph vessel density, remodeling, and inflammation are reflected by gene expression signatures in dermal lymphatic endothelial cells in type 2 diabetes

Type 2 diabetes is associated with microvascular damage that causes frequent infections in the skin and chronic ulcers as a result of impaired wound healing. To trace the pathological changes, we performed a comprehensive analysis of lymphatic vessels in the skin of type 2 diabetic versus nondiabetic patients. The dermis revealed enhanced lymphatic vessel density, and transcriptional profiling of ex vivo isolated lymphatic endothelial cells (LECs) identified 160 genes differentially expressed between type 2 diabetic and nondiabetic LECs. Bioinformatic analysis of deregulated genes uncovered sets functionally related to inflammation, lymphatic vessel remodeling, lymphangiogenesis, and lipid and small molecule transport. Furthermore, we traced CD68(+) macrophage accumulation and concomitant upregulation of tumor necrosis factor-α (TNF-α) levels in type 2 diabetic skin. TNF-α treatment of LECs and its specific blockade in vitro reproduced differential regulation of a gene set that led to enhanced LEC mobility and macrophage attachment, which was mediated by the LEC-derived chemokine CXCL10. This study identifies lymph vessel gene signatures directly correlated with type 2 diabetes skin manifestations. In addition, we provide evidence for paracrine cross-talk fostering macrophage recruitment to LECs as one pathophysiological process that might contribute to aberrant lymphangiogenesis and persistent inflammation in the skin.

Cutaneous wound healing after treatment with plant-derived human recombinant collagen flowable gel

Chronic wounds, particularly diabetic ulcers, represent a main public health concern with significant costs. Ulcers often harbor an additional obstacle in the form of tunneled or undermined wounds, requiring treatments that can reach the entire wound tunnel, because bioengineered grafts are typically available only in a sheet form. While collagen is considered a suitable biodegradable scaffold material, it is usually extracted from animal and human cadaveric sources, and accompanied by potential allergic and infectious risks. The purpose of this study was to test the performance of a flowable gel made of human recombinant type I collagen (rhCollagen) produced in transgenic tobacco plants, indicated for the treatment of acute, chronic, and tunneled wounds. The performance of the rhCollagen flowable gel was tested in an acute full-thickness cutaneous wound-healing rat model and compared to saline treatment and two commercial flowable gel control products made of bovine collagen and cadaver human skin collagen. When compared to the three control groups, the rhCollagen-based gel accelerated wound closure and triggered a significant jumpstart to the healing process, accompanied by enhanced re-epithelialization. In a cutaneous full-thickness wound pig model, the rhCollagen-based flowable gel induced accelerated wound healing compared to a commercial product made of bovine tendon collagen. By day 21 post-treatment, 95% wound closure was observed with the rhCollagen product compared to 68% closure in wounds treated with the reference product. Moreover, rhCollagen treatment induced an early angiogenic response and induced a significantly lower inflammatory response than in the control group. In summary, rhCollagen flowable gel proved to be efficacious in animal wound models and is expected to be capable of reducing the healing time of human wounds.

Mast cell activity in the healing wound: more than meets the eye?

Mast cells (MCs) are an important part of the innate immune system and are abundant in barrier organs such as the skin. They are known primarily for initiating allergic reactions, but many other biological functions have now been described for these cells. Studies have indicated that during wound repair, MCs enhance acute inflammation, stimulate reepithelialization and angiogenesis, and promote scarring. MCs have also been linked to abnormal healing, with high numbers of MCs observed in chronic wounds, hypertrophic scars and keloids. Although MCs have gained attention in the wound healing field, several unique features of MCs have yet to be examined in the context of cutaneous repair. These include the ability of MCs to: (i) produce anti-inflammatory mediators; (ii) release mediators without degranulating; and (iii) change their phenotype. Recent findings highlight the complexity of MCs and suggest that more information is needed to understand their complete range of activities during repair.

Increased saturated fatty acids in obesity alter resolution of inflammation in part by stimulating prostaglandin production

Extensive evidence indicates that nutrient excess associated with obesity and type 2 diabetes activates innate immune responses that lead to chronic, sterile low-grade inflammation, and obese and diabetic humans also have deficits in wound healing and increased susceptibility to infections. Nevertheless, the mechanisms that sustain unresolved inflammation during obesity remain unclear. In this study, we report that saturated free fatty acids that are elevated in obesity alter resolution of acute sterile inflammation by promoting neutrophil survival and decreasing macrophage phagocytosis. Using a targeted mass spectrometry-based lipidomics approach, we found that in db/db mice, PGE2/D2 levels were elevated in inflammatory exudates during the development of acute peritonitis. Moreover, in isolated macrophages, palmitic acid stimulated cyclooxygenase-2 induction and prostanoid production. Defects in macrophage phagocytosis induced by palmitic acid were mimicked by PGE2 and PGD2 and were reversed by cyclooxygenase inhibition or prostanoid receptor antagonism. Macrophages isolated from obese-diabetic mice expressed prostanoid receptors, EP2 and DP1, and contained significantly higher levels of downstream effector, cAMP, compared with wild-type mice. Therapeutic administration of EP2/DP1 dual receptor antagonist, AH6809, decreased neutrophil accumulation in the peritoneum of db/db mice, as well as the accumulation of apoptotic cells in the thymus. Taken together, these studies provide new insights into the mechanisms underlying altered innate immune responses in obesity and suggest that targeting specific prostanoid receptors may represent a novel strategy for resolving inflammation and restoring phagocyte defects in obese and diabetic individuals.

A modified collagen gel enhances healing outcome in a preclinical swine model of excisional wounds

Collagen-based dressings are of great interest in wound care. However, evidence supporting their mechanism of action is scanty. This work provides first results from a preclinical swine model of excisional wounds, elucidating the mechanism of action of a modified collagen gel (MCG) dressing. Following wounding, wound-edge tissue was collected at specific time intervals (3, 7, 14, and 21 days postwounding). On day 7, histological analysis showed significant increase in the length of rete ridges, suggesting improved biomechanical properties of the healing wound tissue. Rapid and transient mounting of inflammation is necessary for efficient healing. MCG significantly accelerated neutrophil and macrophage recruitment to the wound site on day 3 and day 7 with successful resolution of inflammation on day 21. MCG induced monocyte chemotactic protein-1 expression in neutrophil-like human promyelocytic leukemia-60 cells in vitro. In vivo, MCG-treated wound tissue displayed elevated vascular endothelial growth factor expression. Consistently, MCG-treated wounds displayed significantly higher abundance of endothelial cells with increased blood flow to the wound area indicating improved vascularization. This observation was explained by the finding that MCG enhanced proliferation of wound-site endothelial cells. In MCG-treated wound tissue, Masson's trichrome and picrosirius red staining showed higher abundance of collagen and increased collagen type I:III ratio. This work presents first evidence from a preclinical setting explaining how a collagen-based dressing may improve wound closure by targeting multiple key mechanisms. The current findings warrant additional studies to determine whether the responses to the MCG are different from other collagen-based products used in clinical setting.

Macrophage ADAM17 deficiency augments CD36-dependent apoptotic cell uptake and the linked anti-inflammatory phenotype

RATIONALE

Apoptotic cell phagocytosis (efferocytosis) is mediated by specific receptors and is essential for resolution of inflammation. In chronic inflammation, apoptotic cell clearance is dysfunctional and soluble levels of several apoptotic cell receptors are elevated. Reports have identified proteolytic cleavage as a mechanism capable of releasing soluble apoptotic cell receptors, but the functional implications of their proteolysis are unclear.

OBJECTIVE

To test the hypothesis that ADAM17-mediated cleavage of apoptotic cell receptors limits efferocytosis in vivo.

METHODS AND RESULTS

In vivo comparison of macrophage efferocytosis in wild-type and Adam17-null hematopoietic chimeras demonstrates that ADAM17 deficiency leads to a 60% increase in efferocytosis and an enhanced anti-inflammatory phenotype in a model of peritonitis. In vitro uptake of phosphatidylserine liposomes identifies the dual-pass apoptotic cell receptor CD36 as a major contributor to enhanced efferocytosis, and CD36 surface levels are elevated on macrophages from Adam17-null mice. Further, temporal elevation of CD36 expression with inflammation may also contribute to its impact. Soluble CD36 from macrophage-conditioned media comprises 2 species based on Western blotting, and mass spectrometry identifies 3 N-terminal peptides that represent probable cleavage sites. Levels of soluble CD36 are decreased in Adam17-null conditioned media, providing evidence for involvement of ADAM17 in CD36 cleavage. Importantly, enhanced efferocytosis in vivo by macrophages lacking ADAM17 is CD36 dependent and accelerates macrophage clearance from the peritoneum, thus promoting resolution of inflammation and highlighting the impact of increased apoptotic cell uptake.

CONCLUSIONS

Our studies demonstrate the importance of ADAM17-mediated proteolysis for in vivo efferocytosis regulation and suggest a possible mechanistic link between chronic inflammation and defective efferocytosis.

Biomolecular signatures of diabetic wound healing by structural mass spectrometry

Wound fluid is a complex biological sample containing byproducts associated with the wound repair process. Contemporary techniques, such as immunoblotting and enzyme immunoassays, require extensive sample manipulation and do not permit the simultaneous analysis of multiple classes of biomolecular species. Structural mass spectrometry, implemented as ion mobility-mass spectrometry (IM-MS), comprises two sequential, gas-phase dispersion techniques well suited for the study of complex biological samples because of its ability to separate and simultaneously analyze multiple classes of biomolecules. As a model of diabetic wound healing, poly(vinyl alcohol) sponges were inserted subcutaneously into nondiabetic (control) and streptozotocin-induced diabetic rats to elicit a granulation tissue response and to collect acute wound fluid. Sponges were harvested at days 2 or 5 to capture different stages of the early wound-healing process. Utilizing IM-MS, statistical analysis, and targeted ultraperformance liquid chromatography analysis, biomolecular signatures of diabetic wound healing have been identified. The protein S100-A8 was highly enriched in the wound fluids collected from day 2 diabetic rats. Lysophosphatidylcholine (20:4) and cholic acid also contributed significantly to the differences between diabetic and control groups. This report provides a generalized workflow for wound fluid analysis demonstrated with a diabetic rat model.

Proresolution therapy for the treatment of delayed healing of diabetic wounds

Obesity and type 2 diabetes are emerging global epidemics associated with chronic, low-grade inflammation. A characteristic feature of type 2 diabetes is delayed wound healing, which increases the risk of recurrent infections, tissue necrosis, and limb amputation. In health, inflammation is actively resolved by endogenous mediators, such as the resolvins. D-series resolvins are generated from docosahexaenoic acid (DHA) and promote macrophage-mediated clearance of microbes and apoptotic cells. However, it is not clear how type 2 diabetes affects the resolution of inflammation. Here, we report that resolution of acute peritonitis is delayed in obese diabetic (db/db) mice. Altered resolution was associated with decreased apoptotic cell and Fc receptor-mediated macrophage clearance. Treatment with resolvin D1 (RvD1) enhanced resolution of peritonitis, decreased accumulation of apoptotic thymocytes in diabetic mice, and stimulated diabetic macrophage phagocytosis. Conversion of DHA to monohydroxydocosanoids, markers of resolvin biosynthesis, was attenuated in diabetic wounds, and local application of RvD1 accelerated wound closure and decreased accumulation of apoptotic cells and macrophages in the wounds. These findings support the notion that diabetes impairs resolution of wound healing and demonstrate that stimulating resolution with proresolving lipid mediators could be a novel approach to treating chronic, nonhealing wounds in patients with diabetes.

Subchondral pre-solidified chitosan/blood implants elicit reproducible early osteochondral wound-repair responses including neutrophil and stromal cell chemotaxis, bone resorption and repair, enhanced repair tissue integration and delayed matrix deposition

Background

In this study we evaluated a novel approach to guide the bone marrow-driven articular cartilage repair response in skeletally aged rabbits. We hypothesized that dispersed chitosan particles implanted close to the bone marrow degrade in situ in a molecular mass-dependent manner, and attract more stromal cells to the site in aged rabbits compared to the blood clot in untreated controls.

Methods

Three microdrill hole defects, 1.4 mm diameter and 2 mm deep, were created in both knee trochlea of 30 month-old New Zealand White rabbits. Each of 3 isotonic chitosan solutions (150, 40, 10 kDa, 80% degree of deaceylation, with fluorescent chitosan tracer) was mixed with autologous rabbit whole blood, clotted with Tissue Factor to form cylindrical implants, and press-fit in drill holes in the left knee while contralateral holes received Tissue Factor or no treatment. At day 1 or day 21 post-operative, defects were analyzed by micro-computed tomography, histomorphometry and stereology for bone and soft tissue repair.

Results

All 3 implants filled the top of defects at day 1 and were partly degraded in situ at 21 days post-operative. All implants attracted neutrophils, osteoclasts and abundant bone marrow-derived stromal cells, stimulated bone resorption followed by new woven bone repair (bone remodeling) and promoted repair tissue-bone integration. 150 kDa chitosan implant was less degraded, and elicited more apoptotic neutrophils and bone resorption than 10 kDa chitosan implant. Drilled controls elicited a poorly integrated fibrous or fibrocartilaginous tissue.

Conclusions

Pre-solidified implants elicit stromal cells and vigorous bone plate remodeling through a phase involving neutrophil chemotaxis. Pre-solidified chitosan implants are tunable by molecular mass, and could be beneficial for augmented marrow stimulation therapy if the recruited stromal cells can progress to bone and cartilage repair.

Novel animal models for tracking the fate and contributions of bone marrow derived cells in diabetic healing

There is a vast wealth of information to be gained by tracking both the fate and contribution of individual cell types to the wound healing response. This is particularly important in research focused on impaired healing, such as diabetic wound healing, where the number or function of one or more specific cell types may be abnormal and contribute to the observed healing derangements. Specifically, diabetic wounds have been shown to have an overactive inflammatory response and decreased angiogenesis. The ability to track specific cell types participating in these responses would dramatically improve our understanding of the cellular derangements in diabetic healing. In this chapter, we review two novel chimeric models based on the leptin deficient Db/Db mouse. The use of these models allows for the tracking of bone marrow derived inflammatory and progenitor cell populations as well as the determination of the molecular contributions of these cell populations to the wound healing response.

Wound bed preparation from a clinical perspective

Wound bed preparation has been performed for over two decades, and the concept is well accepted. The ‘TIME’ acronym, consisting of tissue debridement, infection or inflammation, moisture balance and edge effect, has assisted clinicians systematically in wound assessment and management. While the focus has usually been concentrated around the wound, the evolving concept of wound bed preparation promotes the treatment of the patient as a whole. This article discusses wound bed preparation and its clinical management components along with the principles of advanced wound care management at the present time. Management of tissue necrosis can be tailored according to the wound and local expertise. It ranges from simple to modern techniques like wet to dry dressing, enzymatic, biological and surgical debridement. Restoration of the bacterial balance is also an important element in managing chronic wounds that are critically colonized. Achieving a balance moist wound will hasten healing and correct biochemical imbalance by removing the excessive enzymes and growth factors. This can be achieved will multitude of dressing materials. The negative pressure wound therapy being one of the great breakthroughs. The progress and understanding on scientific basis of the wound bed preparation over the last two decades are discussed further in this article in the clinical perspectives.

Epigenetic mechanisms in the pathogenesis of diabetic foot ulcers

The incidence of diabetes mellitus, a chronic metabolic disease associated with both predisposing genetic and environmental factors, is increasing globally. As a result, it is expected that there will also be an increasing incidence of diabetic complications which arise as a result of poor glycemic control. Complications include cardiovascular diseases, nephropathy, retinopathy and diabetic foot ulcers. The findings of several major clinical trials have identified that diabetic complications may arise even after many years of proper glycemic control. This has led to the concept of persistent epigenetic changes. Various epigenetic mechanisms have been identified as important contributors to the pathogenesis of diabetes and diabetic complications. The aim of this review is to provide an overview of the pathobiology of type 2 diabetes with an emphasis on complications, particularly diabetic foot ulcers. An overview of epigenetic mechanisms is provided and the focus is on the emerging evidence for aberrant epigenetic mechanisms in diabetic foot ulcers.

Secondary intracerebral hemorrhage due to early initiation of oral anticoagulation after ischemic stroke: an experimental study in mice

BACKGROUND AND PURPOSE

The uncertain risk of secondary intracerebral hemorrhage (sICH) frequently keeps clinicians from initiating oral anticoagulation (OAC) early after ischemic cardioembolic stroke. The goal of this experimental study was to determine the risk of sICH depending on the timing of OAC initiation relative to stroke onset and to address the role of hematogenous macrophages for repair processes preventing OAC-associated sICH.

METHODS

C57BL/6 mice were subjected to transient middle cerebral artery occlusion. Subgroups were treated with either the vitamin K antagonist (VKA) phenprocoumon or the direct thrombin inhibitor dabigatran etexilate. Hematogenous macrophages were depleted using intraperitoneal injections of clodronate-filled liposomes.

RESULTS

Time to therapeutic OAC was 48 hours with VKA and 0.5 hours with dabigatran etexilate treatment. In VKA-treated mice, the risk of sICH was high if effective OAC was already present at stroke onset or achieved within 48 hours after ischemia. With more delayed OAC, the risk of sICH rapidly decreased. Compared with VKA treatment, effective anticoagulation with dabigatran etexilate was associated with a significantly reduced extent of sICH, either if present at stroke onset or if achieved 48 hours later. Partial depletion of macrophages greatly increased the extent of OAC-associated sICH in the subacute stage of 3 to 4 days after ischemia.

CONCLUSIONS

Our findings suggest that repair mechanisms involving hematogenous macrophages rapidly decrease the risk of OAC-associated sICH in the first days after ischemic stroke. The lower risk of sICH under dabigatran etexilate compared with VKA treatment may facilitate early initiation of OAC after cardioembolic stroke.