Macrophage PPARγ and impaired wound healing in type 2 diabetes

Collagen/hyaluronan based hydrogels releasing sulfated hyaluronan improve dermal wound healing in diabetic mice via reducing inflammatory macrophage activity

Sustained inflammation associated with dysregulated macrophage activation prevents tissue formation and healing of chronic wounds. Control of inflammation and immune cell functions thus represents a promising approach in the development of advanced therapeutic strategies. Here we describe immunomodulatory hyaluronan/collagen (HA-AC/coll)-based hydrogels containing high-sulfated hyaluronan (sHA) as immunoregulatory component for the modulation of inflammatory macrophage activities in disturbed wound healing. Solute sHA downregulates inflammatory activities of bone marrow-derived and tissue-resident macrophages in vitro. This further affects macrophage-mediated pro-inflammatory activation of skin cells as shown in skin ex-vivo cultures. In a mouse model of acute skin inflammation, intradermal injection of sHA downregulates the inflammatory processes in the skin. This is associated with the promotion of an anti-inflammatory gene signature in skin macrophages indicating a shift of their activation profile. For in vivo translation, we designed HA-AC/coll hydrogels allowing delivery of sHA into wounds over a period of at least one week. Their immunoregulatory capacity was analyzed in a translational experimental approach in skin wounds of diabetic db/db mice, an established model for disturbed wound healing. The sHA-releasing hydrogels improved defective tissue repair with reduced inflammation, augmented pro-regenerative macrophage activation, increased vascularization, and accelerated new tissue formation and wound closure.

Recovery of Altered Diabetic Myofibroblast Heterogeneity and Gene Expression Are Associated with CD301b+ Macrophages

Diabetic wound healing is associated with impaired function and reduced numbers of myofibroblasts, a heterogeneous cell population with varying capacities to promote repair. To determine how diabetes alters myofibroblast composition, we performed flow cytometry and spatial tissue analysis of myofibroblast subsets throughout the healing process in diabetic (db/db) and control (db/+) mouse skin. We observed reduced numbers of profibrotic SCA1+; CD34+; CD26+ myofibroblasts in diabetic wounds five days after injury, with decreased expression of fibrosis-associated genes compared to myofibroblasts from db/+ mouse wounds. While the abundance of myofibroblasts remained reduced in db/db mouse wounds compared to controls, the altered myofibroblast heterogeneity and gene expression in diabetic mice was improved seven days after injury. The natural correction of myofibroblast composition and gene expression in db/db wound beds temporally corresponds with a macrophage phenotypic switch. Correlation analysis from individual wound beds revealed that wound healing in control mice is associated with CD206+ macrophages, while the rescued myofibroblast phenotypes in diabetic wounds are correlated with increased CD301b+ macrophage numbers. These data demonstrate how diabetes impacts specific subsets of myofibroblasts and indicate that signaling capable of rescuing impaired diabetic wound healing could be different from signals that regulate wound healing under nonpathological conditions.

High-fat diet-associated cognitive decline: Is zinc finger protein 1 (ZPR1) the molecular connection?

Zinc finger protein 1 (ZPR1) is required for cellular replication and viability. Recently, ZPR1 variant rs964184 has been repeatedly linked to high plasma triglyceride levels, metabolic syndrome, type 2 diabetes mellitus (T2DM), and nonalcoholic fatty liver disease (NAFLD), suggesting its involvement in lipid metabolism. This article attempts to explain how ZPR1 contributes to the mechanism of high-fat diet-associated cognitive decline through three premises: i) high-fat diet results in cognitive decline, ii) ZPR1 deficiency also results in cognitive decline, and iii) high-fat diet results in ZPR1 deficiency. Therefore, ZPR1 has the potential to be the connection between high-fat diet and cognitive decline. The two modalities of cognitive decline caused by low concentrations of ZPR1 are reduced brain-derived growth factor (BDNF) synthesis and neuron death, both occurring in the hippocampus. Downregulation of ZPR1 may lead to decreased synthesis of BDNF due to reduced concentrations of peroxisome proliferator-activated receptor-gamma (PPAR-γ), tropomyosin receptor kinase B (Trk B), and cAMP response element-binding protein (CREB), resulting in reduced ability to form and retain long-term memory as well as reduced neuroplasticity. Likewise, low concentrations of ZPR1 facilitate neuron death by producing lower amount of spinal motor neuron (SMN) protein, causing genomic instability, activating mixed-lineage protein kinase 3 (MLK3), mitogen-activated protein kinase 7 (MKK7), and c-Jun N-terminal kinase 3 (JNK3) signal cascade, and ultimately resulting in the activation of Caspase 3.

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ZPR1 plays an important role in cell division and viability.

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ZPR1 variant rs964184 has been linked to dysregulation of lipid metabolism.

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High-fat diet can reduce ZPR1 to induce hippocampal neuronal death.

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High-fat diet correlates with cognitive decline.

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ZPR1 may mediate high-fat diet-induced cognitive decline.

Diabetic Wound-Healing Science

Diabetes mellitus is an increasingly prevalent chronic metabolic disease characterized by prolonged hyperglycemia that leads to long-term health consequences. It is estimated that impaired healing of diabetic wounds affects approximately 25% of all patients with diabetes mellitus, often resulting in lower limb amputation, with subsequent high economic and psychosocial costs. The hyperglycemic environment promotes the formation of biofilms and makes diabetic wounds difficult to treat. In this review, we present updates regarding recent advances in our understanding of the pathophysiology of diabetic wounds focusing on impaired angiogenesis, neuropathy, sub-optimal chronic inflammatory response, barrier disruption, and subsequent polymicrobial infection, followed by current and future treatment strategies designed to tackle the various pathologies associated with diabetic wounds. Given the alarming increase in the prevalence of diabetes, and subsequently diabetic wounds, it is imperative that future treatment strategies target multiple causes of impaired healing in diabetic wounds.

Modulation of macrophage functions by ECM-inspired wound dressings - a promising therapeutic approach for chronic wounds

Nonhealing chronic wounds are among the most common skin disorders with increasing incidence worldwide. However, their treatment is still dissatisfying, that is why novel therapeutic concepts targeting the sustained inflammatory process have emerged. Increasing understanding of chronic wound pathologies has put macrophages in the spotlight of such approaches. Herein, we review current concepts and perspectives of therapeutic macrophage control by ECM-inspired wound dressing materials. We provide an overview of the current understanding of macrophage diversity with particular view on their roles in skin and in physiological and disturbed wound healing processes. Based on this we discuss strategies for their modulation in chronic wounds and how such strategies can be tailored in ECM-inspired wound dressing. The latter utilize and mimic general principles of ECM-mediated cell control, such as binding and delivery of signaling molecules and direct signaling to cells specifically adapted for macrophage regulation in wounds. In this review, we present examples of most recent approaches and discuss ideas for their further development.

[Nutrition in the prevention and healing of chronic wounds. Importance in improving the diabetic foot]

Nutrition plays an essential role in chronic wound healing as extra nutrients are needed for tissue repair and to restore losses through wound exudate. Insufficient intake of energy, protein, antioxidants (vitamin C, A, and zinc) and vitamin D are common in patients with chronic wounds and have been linked to delayed wound healing and dehiscence. Other risk factors such as obesity, diabetes, advanced age, corticosteroid use, and dehydration can also reduce or impede the healing process, and nutritional screening is important to identify patients with malnutrition. Proteins, amino acids (arginine, glutamine and methionine), vitamins C and A, and zinc have been used as pharmacological nutrients in pressure ulcer healing; however, omega-3 fatty acids, although they appear to slow progression, do not show improved healing rates. In patients with diabetic foot, supplementation with vitamins D, C, A, and E, magnesium, zinc, omega-3 fatty acids, and probiotics reduces ulcer size and improves glycemic control, although they have not been associated with complete healing; however, supplementation with arginine, glutamine, and β-hydroxy-β-methylbutyrate does show wound healing, although further evidence is needed to confirm these results.

The influence of a biofilm-dispersing wound gel on the wound healing process

Topical antimicrobials that reduce the bacterial bioburden within a chronically‐infected wound may have helpful or harmful effects on the healing process. We used murine models of full‐thickness skin wounds to determine the effects of the novel biofilm‐dispersing wound gel (BDWG) and its gel base on the healing of uninfected wounds. The rate of wound closure over 19 days was comparable among the BDWG‐treated (BT) wounds and the controls. Compared with the controls, histology of the BT wounds showed formation of a stable blood clot at day 1, more neovascularisation and reepithelialisation at day 3, and more organised healing at day 7. Fluorescence‐activated cell sorting analysis showed a lower percentage of neutrophils in wounded tissues of the BT group at days 1 and 3, and significantly more M2 macrophages at day 3. Levels of proinflammatory cytokines and chemokines were increased over the uninjured baseline within the wounds of all treatment groups but the levels were significantly lower in the BT group at day 1, modulating the inflammatory response. Our results suggest that BDWG does not interfere with the wound healing process and may enhance it by lowering inflammation and allowing transition to the proliferative stage of wound healing by day 3.

The role of lipid-based signalling in wound healing and senescence

Lipid-based signalling modulates several cellular processes and intercellular communication during wound healing and tissue regeneration. Bioactive lipids include but are not limited to the diverse group of eicosanoids, phospholipids, and extracellular vesicles and mediate the attraction of immune cells, initiation of inflammatory responses, and their resolution. In aged individuals, wound healing and tissue regeneration are greatly impaired, resulting in a delayed healing process and non-healing wounds. Senescent cells accumulate with age in vivo, preferably at sites implicated in age-associated pathologies and their elimination was shown to alleviate many age-associated diseases and disorders. In contrast to these findings, the transient presence of senescent cells in the process of wound healing exerts beneficial effects and limits fibrosis. Hence, clearance of senescent cells during wound healing was repeatedly shown to delay wound closure in vivo. Recent findings established a dysregulated synthesis of eicosanoids, phospholipids and extracellular vesicles as part of the senescent phenotype. This intriguing connection between cellular senescence, lipid-based signalling, and the process of wound healing and tissue regeneration prompts us to compile the current knowledge in this review and propose future directions for investigation.

Novel Applications of NSAIDs: Insight and Future Perspectives in Cardiovascular, Neurodegenerative, Diabetes and Cancer Disease Therapy

Once it became clear that inflammation takes place in the modulation of different degenerative disease including neurodegenerative, cardiovascular, diabetes and cancer the researchers has started intensive programs evaluating potential role of non-steroidal anti-inflammatory drugs (NSAIDs) in the prevention or therapy of these diseases. This review discusses the novel mechanism of action of NSAIDs and its potential use in the pharmacotherapy of neurodegenerative, cardiovascular, diabetes and cancer diseases. Many different molecular and cellular factors which are not yet fully understood play an important role in the pathogenesis of inflammation, axonal damage, demyelination, atherosclerosis, carcinogenesis thus further NSAID studies for a new potential indications based on precise pharmacotherapy model are warranted since NSAIDs are a heterogeneous group of medicines with relative different pharmacokinetics and pharmacodynamics profiles. Hopefully the new data from studies will fill in the gap between experimental and clinical results and translate our knowledge into successful disease therapy.

Macrophage Related Chronic Inflammation in Non-Healing Wounds

Persistent hyper-inflammation is a distinguishing pathophysiological characteristic of chronic wounds, and macrophage malfunction is considered as a major contributor thereof. In this review, we describe the origin and heterogeneity of macrophages during wound healing, and compare macrophage function in healing and non-healing wounds. We consider extrinsic and intrinsic factors driving wound macrophage dysregulation, and review systemic and topical therapeutic approaches for the restoration of macrophage response. Multidimensional analysis is highlighted through the integration of various high-throughput technologies, used to assess the diversity and activation states as well as cellular communication of macrophages in healing and non-healing wound. This research fills the gaps in current literature and provides the promising therapeutic interventions for chronic wounds.

The Emerging Role of COX-2, 15-LOX and PPARγ in Metabolic Diseases and Cancer: An Introduction to Novel Multi-target Directed Ligands (MTDLs)

Emerging evidence supports an intertwining framework for the involvement of different inflammatory pathways in a common pathological background for a number of disorders. Of importance are pathways involving arachidonic acid metabolism by cyclooxygenase-2 (COX-2) and 15-lipoxygenase (15-LOX). Both enzyme activities and their products are implicated in a range of pathophysiological processes encompassing metabolic impairment leading to adipose inflammation and the subsequent vascular and neurological disorders, in addition to various pro- and antitumorigenic effects. A further layer of complexity is encountered by the disparate, and often reciprocal, modulatory effect COX-2 and 15-LOX activities and metabolites exert on each other or on other cellular targets, the most prominent of which is peroxisome proliferator-activated receptor gamma (PPARγ). Thus, effective therapeutic intervention with such multifaceted disorders requires the simultaneous modulation of more than one target. Here, we describe the role of COX-2, 15-LOX, and PPARγ in cancer and complications of metabolic disorders, highlight the value of designing multi-target directed ligands (MTDLs) modifying their activity, and summarizing the available literature regarding the rationale and feasibility of design and synthesis of these ligands together with their known biological effects. We speculate on the potential impact of MTDLs in these disorders as well as emphasize the need for structured future effort to translate these early results facilitating the adoption of these, and similar, molecules in clinical research.

The Dynamic Inflammatory Tissue Microenvironment: Signality and Disease Therapy by Biomaterials

Tissue regeneration is an active multiplex process involving the dynamic inflammatory microenvironment. Under a normal physiological framework, inflammation is necessary for the systematic immunity including tissue repair and regeneration as well as returning to homeostasis. Inflammatory cellular response and metabolic mechanisms play key roles in the well-orchestrated tissue regeneration. If this response is dysregulated, it becomes chronic, which in turn causes progressive fibrosis, improper repair, and autoimmune disorders, ultimately leading to organ failure and death. Therefore, understanding of the complex inflammatory multiple player responses and their cellular metabolisms facilitates the latest insights and brings novel therapeutic methods for early diseases and modern health challenges. This review discusses the recent advances in molecular interactions of immune cells, controlled shift of pro- to anti-inflammation, reparative inflammatory metabolisms in tissue regeneration, controlling of an unfavorable microenvironment, dysregulated inflammatory diseases, and emerging therapeutic strategies including the use of biomaterials, which expand therapeutic views and briefly denote important gaps that are still prevailing.

PPAR Gamma: From Definition to Molecular Targets and Therapy of Lung Diseases

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor superfamily that regulate the expression of genes related to lipid and glucose metabolism and inflammation. There are three members: PPARα, PPARβ or PPARγ. PPARγ have several ligands. The natural agonists are omega 9, curcumin, eicosanoids and others. Among the synthetic ligands, we highlight the thiazolidinediones, clinically used as an antidiabetic. Many of these studies involve natural or synthetic products in different pathologies. The mechanisms that regulate PPARγ involve post-translational modifications, such as phosphorylation, sumoylation and ubiquitination, among others. It is known that anti-inflammatory mechanisms involve the inhibition of other transcription factors, such as nuclear factor kB(NFκB), signal transducer and activator of transcription (STAT) or activator protein 1 (AP-1), or intracellular signaling proteins such as mitogen-activated protein (MAP) kinases. PPARγ transrepresses other transcription factors and consequently inhibits gene expression of inflammatory mediators, known as biomarkers for morbidity and mortality, leading to control of the exacerbated inflammation that occurs, for instance, in lung injury/acute respiratory distress. Many studies have shown the therapeutic potentials of PPARγ on pulmonary diseases. Herein, we describe activities of the PPARγ as a modulator of inflammation, focusing on lung injury and including definition and mechanisms of regulation, biological effects and molecular targets, and its role in lung diseases caused by inflammatory stimuli, bacteria and virus, and molecular-based therapy.

Toward Developing Immunocompetent Diabetic Foot Ulcer-on-a-Chip Models for Drug Testing

Bioengineering of skin has been significantly explored, ranging from the use of traditional cell culture systems to the most recent organ-on-a-chip (OoC) technology that permits skin modeling on physiological scales among other benefits. This article presents key considerations for developing physiologically relevant immunocompetent diabetic foot ulcer (DFU) models. Diabetic foot ulceration affects hundreds of millions of individuals globally, especially the elderly, and constitutes a major socioeconomic burden. When DFUs are not treated and managed in a timely manner, 15-50% of patients tend to undergo partial or complete amputation of the affected limb. Consequently, at least 40% of such patients die within 5 years postamputation. Currently, therapeutic strategies are actively sought and developed. However, present-day preclinical platforms (animals and in vitro models) are not robust enough to provide reliable data for clinical trials. Insights from published works on immunocompetent skin-on-a-chip models and bioengineering considerations, presented in this article, can inform researchers on how to develop robust OoC models for testing topical therapies such as growth factor-based therapies for DFUs. We propose that immunocompetent DFU-on-a-chip models should be bioengineered using diseased cells derived from individuals; in particular, the pathophysiological contribution of macrophages in diabetic wound healing, along with the typical fibroblasts and keratinocytes, needs to be recapitulated. The ideal model should consist of the following components: diseased cells embedded in reproducible scaffolds, which permit endogenous "diseased" extracellular matrix deposition, and the integration of the derived immunocompetent DFU model onto a microfluidic platform. The proposed DFU platforms will eventually facilitate reliable and robust drug testing of wound healing therapeutics, coupled with reduced clinical trial failure rates. Impact statement Current animal and cell-based systems are not physiologically relevant enough to retrieve reliable results for clinical translation of diabetic foot ulcer (DFU) therapies. Organ-on-a-chip (OoC) technology offers desirable features that could finally enable the vision of modeling DFU for pathophysiological studies and drug testing at a microscale. This article brings together the significant recent findings relevant to developing a minimally functional immunocompetent DFU-on-a-chip model, as wound healing cannot occur without a proper functioning immune response. It looks feasible in the future to recapitulate the stagnant inflammation in DFU (thought to impede wound healing) using OoC, diseased cells, and an endogenously produced extracellular matrix.

The Effect of TISSEEL® on Colorectal Anastomosis Healing Process in a Diabetic Animal Experimental Model

BACKGROUND/AIM

Diabetes mellitus is an established risk factor of colorectal anastomosis failure. The purpose of the present study was to evaluate the effect of TISSEEL® in anastomotic healing.

MATERIALS AND METHODS

Forty male, Sprague-Dawley rats were used. Diabetes was induced in half of them by intraperitoneal injection of Streptozotocin, 60 mg/kg. One week after the injection, animals were operated and a 1 cm segment was removed and an end-to-end hand sewn anastomosis was performed. TISSEEL® was applied in each group (diabetic, non-diabetic) following randomization.

RESULTS

The pathology analysis revealed improved tissue remodeling in the TISSEEL® group, both for the normoglycemic and the diabetic group. Specifically, the extent of inflammation was decreased (p<0.001), whereas fibroblast and collagen formation were improved (p=0.040 and p=0.008). Neovascularization was also improved (p=0.047).

CONCLUSION

Application of TISSEEL® on colorectal anastomoses improves healing in rats that suffer from severe hyperglycemia.

Eicosanoids in Skin Wound Healing

Wound healing is an important process in the human body to protect against external threats. A dysregulation at any stage of the wound healing process may result in the development of various intractable ulcers or excessive scar formation. Numerous factors such as growth factors, cytokines, and chemokines are involved in this process and play vital roles in tissue repair. Moreover, recent studies have demonstrated that lipid mediators derived from membrane fatty acids are also involved in the process of wound healing. Among these lipid mediators, we focus on eicosanoids such as prostaglandins, thromboxane, leukotrienes, and specialized pro-resolving mediators, which are produced during wound healing processes and play versatile roles in the process. This review article highlights the roles of eicosanoids on skin wound healing, especially focusing on the biosynthetic pathways and biological functions, i.e., inflammation, proliferation, migration, angiogenesis, remodeling, and scarring.

Tissue-Specific Role of Macrophages in Noninfectious Inflammatory Disorders

Chronic inflammation may not begin with local tissue disorders, such as hypoxia, but with the accumulation of critically activated macrophages in one site. The purpose of this review is to analyze the data reported in the scientific literature on the features of the functions of macrophages and their contributions to the development of pathology in various tissues during aseptic inflammation in obese subjects. In individuals with obesity, increased migration of monocytes from the peripheral blood to various tissues, the proliferation of resident macrophages and a change in the balance between alternatively activated anti-inflammatory macrophages (M2) and pro-inflammatory classically activated macrophages (M1) towards the latter have been observed. The primary cause of some metabolic pathologies has been precisely identified as the recruitment of macrophages with an altered phenotype, which is probably typical for many other pathologies. Recent studies have identified phenotypes, such as metabolically activated M (MMe), oxidized (Mox), hemoglobin-related macrophages (Mhem and MHb), M4 and neuroimmunological macrophages (NAM, SAM), which directly and indirectly affect energy metabolism. The high heterogeneity of macrophages in tissues contributes to the involvement of these cells in the development of a wide range of immune responses, including pathological ones. The replenishment of tissue-specific macrophages occurs at the expense of infiltrating monocyte-derived macrophages (MoMFs) in the pathological process. The origin of MoMFs from a general precursor retains their common regulatory mechanisms and similar sensitivity to regulatory stimuli. This makes it possible to find universal approaches to the effect on these cells and, as a consequence, universal approaches for the treatment of various pathological conditions.

Accelerated diabetic wound healing by topical application of combination oral antidiabetic agents-loaded nanofibrous scaffolds: An in vitro and in vivo evaluation study

The combination of oral antidiabetic drugs, pioglitazone, metformin, and glibenclamide, which also exhibit the strongest anti-inflammatory action among oral antidiabetic drugs, were loaded into chitosan/gelatin/polycaprolactone (PCL) by electrospinning and polyvinyl pyrrolidone (PVP)/PCL composite nanofibrous scaffolds by pressurized gyration to compare the diabetic wound healing effect. The combination therapies significantly accelerated diabetic wound healing in type-1 diabetic rats and organized densely packed collagen fibers in the dermis, it also showed better regeneration of the dermis and epidermis than single drug-loaded scaffolds with less inflammatory cell infiltration and edema. The formation of the hair follicles started in 14 days only in the combination therapy and lower proinflammatory cytokine levels were observed compared to single drug-loaded treatment groups. The combination therapy increased the wettability and hydrophilicity of scaffolds, demonstrated sustained drug release over 14 days, has high tensile strength and suitable cytocompatibility on L929 (mouse fibroblast) cell and created a suitable area for the proliferation of fibroblast cells. Consequently, the application of metformin and pioglitazone-loaded chitosan/gelatin/PCL nanofibrous scaffolds to a diabetic wound area offer high bioavailability, fewer systemic side effects, and reduced frequency of dosage and amount of drug.

Epigenetic regulation of the PGE2 pathway modulates macrophage phenotype in normal and pathologic wound repair

Macrophages are a primary immune cell involved in inflammation, and their cell plasticity allows for transition from an inflammatory to a reparative phenotype and is critical for normal tissue repair following injury. Evidence suggests that epigenetic alterations play a critical role in establishing macrophage phenotype and function during normal and pathologic wound repair. Here, we find in human and murine wound macrophages that cyclooxygenase 2/prostaglandin E2 (COX-2/PGE2) is elevated in diabetes and regulates downstream macrophage-mediated inflammation and host defense. Using single-cell RNA sequencing of human wound tissue, we identify increased NF-κB-mediated inflammation in diabetic wounds and show increased COX-2/PGE2 in diabetic macrophages. Further, we identify that COX-2/PGE2 production in wound macrophages requires epigenetic regulation of 2 key enzymes in the cytosolic phospholipase A2/COX-2/PGE2 (cPLA2/COX-2/PGE2) pathway. We demonstrate that TGF-β-induced miRNA29b increases COX-2/PGE2 production via inhibition of DNA methyltransferase 3b-mediated hypermethylation of the Cox-2 promoter. Further, we find mixed-lineage leukemia 1 (MLL1) upregulates cPLA2 expression and drives COX-2/PGE2. Inhibition of the COX-2/PGE2 pathway genetically (Cox2fl/fl Lyz2Cre+) or with a macrophage-specific nanotherapy targeting COX-2 in tissue macrophages reverses the inflammatory macrophage phenotype and improves diabetic tissue repair. Our results indicate the epigenetically regulated PGE2 pathway controls wound macrophage function, and cell-targeted manipulation of this pathway is feasible to improve diabetic wound repair.

Skin well-being in diabetes: Role of macrophages

Macrophages are key players in wound healing- along with mediating the acute inflammatory response, macrophages activate cutaneous epithelial cells and promote tissue repair. Diabetes complications, including diabetic chronic wounds, are accompanied by persistent inflammation and macrophage malfunction. Several studies indicate that hyperglycemia induces various alterations that affect macrophage function in wound healing including epigenetic changes, imbalance between pro- and anti-inflammatory modulators, and insensitivity to proliferative stimuli. In this review, we briefly summarize recent studies regarding those alterations and their implications on skin well-being in diabetes.

Bioactive Fatty Acids in the Resolution of Chronic Inflammation in Skin Wounds

Significance: Optimal skin wound healing is crucial for maintaining tissue homeostasis, particularly in response to an injury. The skin immune system is under regulation of mediators such as bioactive lipids and cytokines that can initiate an immune response with controlled inflammation, followed by efficient resolution. However, nutritional deficiency impacts wound healing by hindering fibroblast proliferation, collagen synthesis, and epithelialization, among other crucial functions. In this way, the correct nutritional support of bioactive lipids and of other essential nutrients plays an important role in the outcome of the wound healing process. Recent Advances and Critical Issues: Several studies have revealed the potential role of lipids as a treatment for the healing of skin wounds. Unsaturated fatty acids such as linoleic acid, α-linolenic acid, oleic acid, and most of their bioactive products have shown an effective role as a topical treatment of chronic skin wounds. Their effect, when the treatment starts at day 0, has been observed mainly in the inflammatory phase of the wound healing process. Moreover, some of them were associated with different dressings and were tested for clinical purposes, including pluronic gel, nanocapsules, collagen films and matrices, and polymeric bandages. Therefore, future research is still needed to evaluate these dressing technologies in association with different bioactive fatty acids in a wound healing context. Future Directions: This review summarizes the main results of the available clinical trials and basic research studies and provides evidence-based conclusions. Together, current data encourage the use of bioactive fatty acids for an optimal wound healing resolution.

The Effects of Type 2 Diabetes Mellitus on Organ Metabolism and the Immune System

Metabolic abnormalities such as dyslipidemia, hyperinsulinemia, or insulin resistance and obesity play key roles in the induction and progression of type 2 diabetes mellitus (T2DM). The field of immunometabolism implies a bidirectional link between the immune system and metabolism, in which inflammation plays an essential role in the promotion of metabolic abnormalities (e.g., obesity and T2DM), and metabolic factors, in turn, regulate immune cell functions. Obesity as the main inducer of a systemic low-level inflammation is a main susceptibility factor for T2DM. Obesity-related immune cell infiltration, inflammation, and increased oxidative stress promote metabolic impairments in the insulin-sensitive tissues and finally, insulin resistance, organ failure, and premature aging occur. Hyperglycemia and the subsequent inflammation are the main causes of micro- and macroangiopathies in the circulatory system. They also promote the gut microbiota dysbiosis, increased intestinal permeability, and fatty liver disease. The impaired immune system together with metabolic imbalance also increases the susceptibility of patients to several pathogenic agents such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Thus, the need for a proper immunization protocol among such patients is granted. The focus of the current review is to explore metabolic and immunological abnormalities affecting several organs of T2DM patients and explain the mechanisms, whereby diabetic patients become more susceptible to infectious diseases.

Palmitate-TLR4 signaling regulates the histone demethylase, JMJD3, in macrophages and impairs diabetic wound healing

Chronic macrophage inflammation is a hallmark of type 2 diabetes (T2D) and linked to the development of secondary diabetic complications. T2D is characterized by excess concentrations of saturated fatty acids (SFA) that activate innate immune inflammatory responses, however, mechanism(s) by which SFAs control inflammation is unknown. Using monocyte-macrophages isolated from human blood and murine models, we demonstrate that palmitate (C16:0), the most abundant circulating SFA in T2D, increases expression of the histone demethylase, Jmjd3. Upregulation of Jmjd3 results in removal of the repressive histone methylation (H3K27me3) mark on NFκB-mediated inflammatory gene promoters driving macrophage-mediated inflammation. We identify that the effects of palmitate are fatty acid specific, as laurate (C12:0) does not regulate Jmjd3 and the associated inflammatory profile. Further, palmitate-induced Jmjd3 expression is controlled via TLR4/MyD88-dependent signaling mechanism, where genetic depletion of TLR4 (Tlr4^-/- ) or MyD88 (MyD88^-/- ) negated the palmitate-induced changes in Jmjd3 and downstream NFκB-induced inflammation. Pharmacological inhibition of Jmjd3 using a small molecule inhibitor (GSK-J4) reduced macrophage inflammation and improved diabetic wound healing. Together, we conclude that palmitate contributes to the chronic Jmjd3-mediated activation of macrophages in diabetic peripheral tissue and a histone demethylase inhibitor-based therapy may represent a novel treatment for nonhealing diabetic wounds.

Multilayer Injectable Hydrogel System Sequentially Delivers Bioactive Substances for Each Wound Healing Stage

Wound healing is a dynamic and complex process that contains several sequential phases. However, most of the current drug delivery systems were designed to treat only one certain phase of wound repair, ignoring the fact that every stage plays critical roles in the wound healing process and those critical stages coordinately work to ensure optimal tissue regeneration. Therefore, a delivery system that can precisely meet the requirements of each wound healing stage is desired to enhance tissue regeneration. In this study, an injectable sodium alginate/bioglass (SA/BG) composite hydrogel was used to carry SA microparticles containing a conditioned medium (CM) of cells (SA_CM). Inside the SA_CM microparticles, poly(lactic-co-glycolic acid) (PLGA) microspheres containing pirfenidone (PFD) were encapsulated (PLGA_PFD). This multilayer injectable hydrogel system (SA/BG-SA_CM-PLGA_PFD) was designed to sequentially deliver bioactive molecules for meeting the bioactivity requirement and timeline of each wound healing stage. First, SA/BG hydrogels could rapidly release BG ionic products in the first 1-3 days to regulate the inflammatory response of the host and initiate the subsequent tissue regeneration. Then, SA_CM hydrogel microparticles could release CM of RAW 264.7 cells stimulated with BG ionic products in 2-7 days to facilitate the formation of the vascularized granulation tissue. Finally, PLGA_PFD microspheres released PFD in 8-20 days to prevent the fibrosis and scar formation in the regenerated skin. Thus, this SA/BG-SA_CM-PLGA_PFD delivery system could restrain host inflammation, accelerate wound healing, and inhibit the fibrosis formation in a diabetic mouse skin damage model, enhancing skin regeneration. As the bioactive components in each layer of the system can be adjusted according to the requirements of different tissue regeneration, this three-layered injectable biomaterial system has a wide application potential in the regenerative medicine field.

Novel fibrin-fibronectin matrix accelerates mice skin wound healing

Plasma fibrinogen (F1) and fibronectin (pFN) polymerize to form a fibrin clot that is both a hemostatic and provisional matrix for wound healing. About 90% of plasma F1 has a homodimeric pair of γ chains (γγF1), and 10% has a heterodimeric pair of γ and more acidic γ' chains (γγ'F1). We have synthesized a novel fibrin matrix exclusively from a 1:1 (molar ratio) complex of γγ'F1 and pFN in the presence of highly active thrombin and recombinant Factor XIII (rFXIIIa). In this matrix, the fibrin nanofibers were decorated with pFN nanoclusters (termed γγ'F1:pFN fibrin). In contrast, fibrin made from 1:1 mixture of γγF1 and pFN formed a sporadic distribution of "pFN droplets" (termed γγF1+pFN fibrin). The γγ'F1:pFN fibrin enhanced the adhesion of primary human umbilical vein endothelium cells (HUVECs) relative to the γγF1+FN fibrin. Three dimensional (3D) culturing showed that the γγ'F1:pFN complex fibrin matrix enhanced the proliferation of both HUVECs and primary human fibroblasts. HUVECs in the 3D γγ'F1:pFN fibrin exhibited a starkly enhanced vascular morphogenesis while an apoptotic growth profile was observed in the γγF1+pFN fibrin. Relative to γγF1+pFN fibrin, mouse dermal wounds that were sealed by γγ'F1:pFN fibrin exhibited accelerated and enhanced healing. This study suggests that a 3D pFN presentation on a fibrin matrix promotes wound healing.

Macrophage Dysregulation and Impaired Skin Wound Healing in Diabetes

Monocytes (Mo) and macrophages (Mϕ) play important roles in normal skin wound healing, and dysregulation of wound Mo/Mϕ leads to impaired wound healing in diabetes. Although skin wound Mϕ originate both from tissue resident Mϕ and infiltrating bone marrow-derived Mo, the latter play dominant roles during the inflammatory phase of wound repair. Increased production of bone marrow Mo caused by alterations of hematopoietic stem and progenitor cell (HSPC) niche and epigenetic modifications of HSPCs likely contributes to the enhanced number of wound Mϕ in diabetes. In addition, an impaired transition of diabetic wound Mϕ from “pro-inflammatory” to “pro-healing” phenotypes driven by the local wound environment as well as intrinsic changes in bone marrow Mo is also thought to be partly responsible for impaired diabetic wound healing. The current brief review describes the origin, heterogeneity and function of wound Mϕ during normal skin wound healing followed by discussion of how dysregulated wound Mϕ numbers and phenotype are associated with impaired diabetic wound healing. The review also highlights the possible links between altered bone marrow myelopoiesis and increased Mo production as well as extrinsic and intrinsic factors that drive wound macrophage dysregulation leading to impaired wound healing in diabetes.

Diabetes and calcification: The potential role of anti-diabetic drugs on vascular calcification regression

Vascular calcification (VC) has been well-established as an independent and strong predictor of cardiovascular diseases (CVD) as well as major cardiac adverse events (MACE). VC is associated with increased mortality in patients with CVD. Pathologically, VC is now believed to be a multi-directional active process ultimately resulting in ectopic calcium deposition in vascular beds. On the other hand, prevalence of diabetes mellitus (DM) is gradually increasing thus making the current population more prone to future CVD. Although the mechanisms involved in development and progression of VC in DM patients are not fully understood, a series of evidences demonstrated positive association between DM and VC. It has been highlighted that different cellular pathways are involved in this process. These intermediates such as tumor necrosis factor alpha (TNF-α), various interleukins (ILs) and different cell-signaling pathways are over-expressed in DM patients leading to development of VC. Thus, considering the burden and significance of VC it is of great importance to find a therapeutic approach to prevent or minimize the development of VC in DM patients. Over the past few years various anti diabetic drugs (ADDs) have been introduced and many of them showed desired glucose control. But no study demonstrated the effects of these medications on regression of VC. In this review, we will briefly discuss the current understanding on DM and VC and how commonly used ADDs modulate the development or progression of VC.

Topical co-administration of Teucrium polium hydroethanolic extract and Aloe vera gel triggered wound healing by accelerating cell proliferation in diabetic mouse model

Diabetic wounds are major issues in patients with diabetes. Medicinal plants of Teucrium polium and Aloe vera have antioxidant and anti-inflammatory properties that may be profitable for diabetic patients. This study was conducted to evaluate the effect of co-administration of ointments prepared from Teucrium polium hydroethanolic extract (TPEO) and Aloe vera gel (AVGO) on excisional wound healing in a diabetic mouse model. Following the induction of diabetes and circular excisional wound (7 mm), the mice were divided into six groups, namely (Ⅰ) control mice treated with mupirocin (as a standard drug), (Ⅱ and Ⅲ) the mice treated with 5 and 10 % TPEO, (Ⅳ and Ⅴ) the mice treated with 5 and 10 % AVGO, and (Ⅵ) the mice treated with a combination of 5% TPEO and 5% AVGO (TPEO+AVGO). To investigate the wound area, we further evaluated the wound area ratio, histological analysis and the serum levels of tissue antioxidant capacity (TAC) and malondialdehyde (MDA), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β), immunohistochemistry staining for vascular endothelial growth factor (VEGF), insulin-like growth factor (IGF-1), glucose transporter-1(GLUT-1) and collagen type 1 and mRNA expression levels for VEGF, IGF-1, GLUT-1 and fibroblast growth factor-2 (FGF-2). The results showed that administration of the ointments, especially in combination form, shortened the inflammatory phase and reduced the levels of tissue MDA, TNF-α and IL-1β compared to mupirocin group (P < 0.05). Moreover, fibroblasts proliferation, collagen deposition, VEGF, IGF-1, GLUT-1-positive cells and level of TAC, and expressions of VEGF, IGF-1, GLUT-1 and FGF-2 were significantly (P < 0.05) increased in TPEO and AVGO, and especially in the mice treated with the mixed form. Therefore, topical co-administration of TPEO + AVGO accelerated open diabetic wound healing through shortening the inflammatory phase and increasing cell proliferation and collagen deposition.

Towards advanced wound regeneration

Wound management is a major contributor towards the economic burden placed upon the national health service (NHS), serving as an important target for the development of advanced therapeutic interventions. The economic expenditure of wound care for the NHS exceeds £5 billion per annum, thus presenting a significant opportunity for the introduction of alternative treatments in regards to their approach in tackling the ever increasing prevalence of wound management associated problems. As most wounds typically fall under the acute or chronic category, it is therefore necessary to design a therapeutic intervention capable of effectively resolving the pathologies associated with each problem. Such an intervention should be of increased economic viability and therapeutic effectiveness when compared to standardized treatments, thus helping to alleviate the financial burden imposed upon the NHS. The purpose of this review is to critically analyse the various aspects associated with wound management, detailing the fundamental concepts of dermal regeneration, whilst also providing an evaluation of the different materials and methods that can be utilised to achieve maximal wound regeneration. The primary aspects of this review revolve around the three concepts of antibacterial methodology, enhancement of dermal regeneration and the utilisation of a carrier medium to facilitate the regenerative process. Each aspect is explored, conveying its justifications as a target for dermal regeneration, whilst offering various solutions towards the fulfilment of a therapeutic design that is both effective and financially feasible.

Pioglitazone-Loaded Nanostructured Hybrid Material for Skin Ulcer Treatment

Pioglitazone, a popular antidiabetic drug, which was recently shown to be effective in the treatment of skin ulcers, was successfully encapsulated in polysaccharide nanoparticles and used as a bioactive component of the wound-dressing material based on modified bacterial nanocellulose. Alginate and hydroxypropyl cellulose were used as a matrix for the nanoparticulate drug-delivery system. The matrix composition and particles’ size, as well as drug encapsulation efficiency and loading, were optimized. Pioglitazone hydrochloride (PIO) loaded particles were coated with chitosan introduced into the crosslinking medium, and covalently attached to the surface of bacterial nanocellulose functionalized with carboxyl groups. PIO was released from the surface of the hybrid material in a controlled manner for 5 days. Preliminary cytotoxicity studies confirmed safety of the system at PIO concentrations as high as 20 mg/mL. The obtained hybrid system may have potential application in the treatment of skin ulcers e.g., in diabetic foot.

Epigenetic Regulation of TLR4 in Diabetic Macrophages Modulates Immunometabolism and Wound Repair

Macrophages are critical for the initiation and resolution of the inflammatory phase of wound healing. In diabetes, macrophages display a prolonged inflammatory phenotype preventing tissue repair. TLRs, particularly TLR4, have been shown to regulate myeloid-mediated inflammation in wounds. We examined macrophages isolated from wounds of patients afflicted with diabetes and healthy controls as well as a murine diabetic model demonstrating dynamic expression of TLR4 results in altered metabolic pathways in diabetic macrophages. Further, using a myeloid-specific mixed-lineage leukemia 1 (MLL1) knockout (Mll1^f/fLyz2^Cre+ ), we determined that MLL1 drives Tlr4 expression in diabetic macrophages by regulating levels of histone H3 lysine 4 trimethylation on the Tlr4 promoter. Mechanistically, MLL1-mediated epigenetic alterations influence diabetic macrophage responsiveness to TLR4 stimulation and inhibit tissue repair. Pharmacological inhibition of the TLR4 pathway using a small molecule inhibitor (TAK-242) as well as genetic depletion of either Tlr4 (Tlr4^-/- ) or myeloid-specific Tlr4 (Tlr4^f/fLyz2^Cre+) resulted in improved diabetic wound healing. These results define an important role for MLL1-mediated epigenetic regulation of TLR4 in pathologic diabetic wound repair and suggest a target for therapeutic manipulation.

Evaluation of burst release and sustained release of pioglitazone-loaded fibrous mats on diabetic wound healing: an in vitro and in vivo comparison study

In order to provide more effective treatment strategies for the rapid healing of diabetic wounds, novel therapeutic approaches need to be developed. The therapeutic potential of peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist pioglitazone hydrochloride (PHR) in two different release kinetic scenarios, burst release and sustained release, was investigated and compared with in vitro and in vivo tests as potential wound healing dressings. PHR-loaded fibrous mats were successfully fabricated using polyvinyl-pyrrolidone and polycaprolactone by scalable pressurized gyration. The results indicated that PHR-loaded fibrous mats expedited diabetic wound healing in type-1 diabetic rats and did not show any cytotoxic effect on NIH/3T3 (mouse embryo fibroblast) cells, albeit with different release kinetics and efficacies. The wound healing effects of fibrous mats are presented with histological and biochemical evaluations. PHR-loaded fibrous mats improved neutrophil infiltration, oedema, and inflammation and increased epidermal regeneration and fibroblast proliferation, but the formation of hair follicles and completely improved oedema were observed only in the sustained release form. Thus, topical administration of PPAR-γ agonist in sustained release form has high potential for the treatment of diabetic wounds in inflammatory and proliferative phases of healing with high bioavailability and fewer systemic side effects.

Intracellular ATP Delivery Causes Rapid Tissue Regeneration via Upregulation of Cytokines, Chemokines, and Stem Cells

We have reported accelerated wound healing induced by intracellular ATP delivery in rabbits, through early massive accumulation, in situ proliferation, and M2 polarization of macrophages. Granulation tissue started to grow within first 24 h of treatment and continued the growth till the wound cavity is completely covered. However, the mechanisms underlying this macrophage response are totally unclear because no one has ever reported this before. In this study, we performed a preliminary exploration of the possible mechanisms by focusing on the roles of cytokines, growth factors, and stem cells in this process. Among the 33 adult rabbits, 18 were used for cytokine measurements and the remaining were used for histological and immunohistochemical studies. Four wounds were created on the ventral side of each ear. Two wounds on one side were treated with ATP-vesicles (10 mM ATP), and the other two were treated with controls (normal saline or Regranex). Dressing changes were made daily and the rabbits were sacrificed at 5 h, 12 h, and 1, 2, 3, 4, 6, 9, 15, and 26 days after wounding. Tissue samples were analyzed for cytokines and growth factors using real-time PCR and immunohistochemical staining. The control wounds showed an immediate increase in proinflammatory cytokines after wound creation but no further increase after this initial spike. The growth factor levels in the control wounds remained unchanged throughout the study. Conversely, the wounds treated with ATP-vesicles showed significantly higher expression of MCP-1 and stem cell markers (CD44, CD106, CD146, and CD34) at day 1, significantly higher IL-1β and TNF-α expression from day 1–4, and significantly higher VEGF-A, VEGF-D, and VEGFR-2 expression from day 4–6 when compared to the controls. The significant upregulation of these factors corresponded to the very early and rapid macrophage accumulation, in situ proliferation, and M2 polarization, resulting in unprecedented rapid granulation tissue generation due to direct macrophage collagen production and neovascularization.

Exaggerated exercise pressor reflex in type 2 diabetes: Potential role of oxidative stress

Type 2 diabetes mellitus (T2DM) leads to exaggerated cardiovascular responses to exercise, in part due to an exaggerated exercise pressor reflex. Accumulating data suggest excessive oxidative stress contributes to an exaggerated exercise pressor reflex in cardiovascular-related diseases. Excessive oxidative stress is also a primary underlying mechanism for the development and progression of T2DM. However, whether oxidative stress plays a role in mediating the exaggerated exercise pressor reflex in T2DM is not known. Therefore, this review explores the potential role of oxidative stress leading to increased activation of the afferent arm of the exercise pressor reflex. Several lines of evidence support direct and indirect effects of oxidative stress on the exercise pressor reflex. For example, intramuscular ROS may directly and indirectly (by attenuating contracting muscle blood flow) increase group III and IV afferent activity. Oxidative stress is a primary underlying mechanism for the development of neuropathic pain, which in turn is associated with increased group III and IV afferent activity. These are the same type of afferents that evoke muscle pain and the exercise pressor reflex. Furthermore, oxidative stress-induced release of inflammatory mediators may modulate afferent activity. Collectively, these alterations may result in a positive feedback loop that further amplifies the exercise pressor reflex. An exaggerated reflex increases the risk of adverse cardiovascular events. Thus, identifying the contribution of oxidative stress could provide a potential therapeutic target to reduce this risk in T2DM.

HuoXueTongFu Formula Alleviates Intraperitoneal Adhesion by Regulating Macrophage Polarization and the SOCS/JAK2/STAT/PPAR-γ Signalling Pathway

Intraperitoneal adhesion is a common complication after abdominal surgery, which seriously affects the quality of life of patients. HuoXueTongFu Formula (HXTF) plays an important role in the prevention and treatment of intraperitoneal adhesions. However, the molecular-related mechanisms are still not fully known. In this study, the model of Intrapetitoneal adhesion was established by cecum abrasion and treated with HXTF for one week. RAW264.7 cells were given LPS, IFN-γ, IL-4, HXTF-medicated serum, and PPAR-γ agonist/antagonist, respectively. Histopathology, flow cytometry, ELISA, real-time PCR, and Western blotting were used to further detect the related protein, M1/M2 polarization tendency, and PPAR-γ nuclear translocation. The deposition of collagen fibres reduced in the local area of rats after the operation with HXTF treatment. Similar to IL-4, HXTF induced a tendency for macrophages to polarize toward M2 and promoted peroxisome proliferator-activated receptor-gamma (PPAR-γ) nuclear translocation. Furthermore, the use of HXTF and PPAR-γ agonists downregulated macrophage M1 polarization-related factors IL-1, IL-6, and TNF-alpha and upregulated M2 polarization-related factors IL-4, IL-10, and TGF-beta 1. Meanwhile, the use of HXTF and PPAR-γ agonists downregulated the SOCS3/JAK2/STAT1 pathway and activated the SOCS1/STAT6/PPAR-γ pathway. These results show that HXTF may reduce intraperitoneal adhesion by inducing macrophage M2 polarization and regulating the SOCS/JAK2/STAT/PPAR-γ pathway.

New Peroxisome Proliferator-Activated Receptor Agonist (GQ-11) Improves Wound Healing in Diabetic Mice

Objective: Chronic wounds associated with diabetes are an important public health problem demanding new treatments to improve wound healing and decrease amputations. Monocytes/macrophages play a key role in sustained inflammation associated with impaired healing and local administration of peroxisome proliferator-activated receptor (PPAR)γ agonists may modulate macrophage, improving healing. In this study, we investigated the effects of GQ-11, a partial/dual PPARα/γ agonist, on macrophage function and wound healing in diabetes. Approach: Wounds were surgically induced at the dorsum of C57BL/6J and BKS.Cg-Dock7^m +/+ Lepr^db/J (db/db) mice and treated with hydrogel (vehicle), pioglitazone or GQ-11, for 7 or 10 days, respectively. After treatment, wounds were analyzed histologically and by quantitative PCR (qPCR). In addition, bone marrow-derived macrophages (BMDM) were cultured from C57BL/6J mice and treated with vehicle, pioglitazone, or GQ-11, after challenge with lipopolysaccharide or interleukin-4 to be analyzed by qPCR and flow cytometry. Results: GQ-11 treatment upregulated anti-inflammatory/pro-healing factors and downregulated pro-inflammatory factors both in wounds of db/db mice and in BMDM. Innovation: Wounds of db/db mice treated with GQ-11 exhibited faster wound closure and re-epithelization, increased collagen deposition, and less Mac-3 staining compared with vehicle, providing a new approach to treatment of diabetic wound healing to prevent complications. Conclusion: GQ-11 improves wound healing in db/db mice, regulating the expression of pro- and anti-inflammatory cytokines and wound growth factors, leading to increased re-epithelization and collagen deposition.

Topical Insulin Modulates Inflammatory and Proliferative Phases of Burn-Wound Healing in Diabetes-Induced Rats

The healing time of burn wounds depends on surface area and depth of the burn and associated comorbidities. Diabetes mellitus (DM) causes delays in the healing process by extending the inflammatory phase. Treatment with topical insulin can improve the inflammatory phase, restore metabolic dysregulation, and modulate impaired cellular signaling in burn wounds. The objective of this study was to evaluate markers of the inflammatory and proliferative phases of second-degree burns after topical insulin treatment in diabetic rats. Type I DM was induced with streptozotocin in male Wistar rats. The animals' backs were shaved and subjected to thermal burning. Rats were randomized into two groups: control diabetic (DC) and insulin diabetic (DI). At Days 7 and 14 postburn, rats were euthanized, and wound-tissue sections were evaluated by hematoxylin and eosin, Weigert, and Verhöeff staining, immunohistochemistry-paraffin, and enzyme-linked immunosorbent assay. A significant increase in reepithelialization was seen on Days 7 and 14 in DI versus DC rats. On Day 7, interleukin (IL)-1β, IL-6, monocyte chemotactic protein (MCP)-1, and F4/80 expression were increased in DI versus DC rats. On Day 14, MCP-1 expression was decreased and F4/80 increased in DI versus DC rats. On Days 7 and 14, Ki-67, transforming growth factor-β1, vascular endothelial growth factor expression, and formation of elastic fibers were increased in DI versus DC rats. Topical insulin modulates burn-wound healing in diabetic animals by balancing inflammation and promoting angiogenesis and formation of elastic fibers.

The Histone Methyltransferase Setdb2 Modulates Macrophage Phenotype and Uric Acid Production in Diabetic Wound Repair

Macrophage plasticity is critical for normal tissue repair to ensure transition from the inflammatory to the proliferative phase of healing. We examined macrophages isolated from wounds of patients afflicted with diabetes and of healthy controls and found differential expression of the methyltransferase Setdb2. Myeloid-specific deletion of Setdb2 impaired the transition of macrophages from an inflammatory phenotype to a reparative one in normal wound healing. Mechanistically, Setdb2 trimethylated histone 3 at NF-κB binding sites on inflammatory cytokine gene promoters to suppress transcription. Setdb2 expression in wound macrophages was regulated by interferon (IFN) β, and under diabetic conditions, this IFNβ-Setdb2 axis was impaired, leading to a persistent inflammatory macrophage phenotype in diabetic wounds. Setdb2 regulated the expression of xanthine oxidase and thereby the uric acid (UA) pathway of purine catabolism in macrophages, and pharmacologic targeting of Setdb2 or the UA pathway improved healing. Thus, Setdb2 regulates macrophage plasticity during normal and pathologic wound repair and is a target for therapeutic manipulation.

PPAR-γ: Its ligand and its regulation by microRNAs

Peroxisome proliferator-activated receptors (PPARs) belong to the nuclear receptor superfamily. PPARs are categorized into three subtypes, PPARα, β/δ, and γ, encoded by different genes, expressed in diverse tissues and participate in various biological functions and can be activated by their metabolic derivatives in the body or dietary fatty acids. The PPAR-γ also takes parts in the regulation of energy balance, lipoprotein metabolism, insulin sensitivity, oxidative stress, and inflammatory signaling. It has been implicated in the pathology of numerous diseases including obesity, diabetes, atherosclerosis, and cancers. Among various cellular and molecular targets that are able to regulate PPAR-γ and its underlying pathways, microRNAs (miRNAs) appeared as important regulators. Given that the deregulation of these molecules via targeting PPAR-γ could affect initiation and progression of various diseases, identification of miRNAs that affects PPAR-γ could contribute to the better understanding of roles of PPAR-γ in various biological and pathological conditions. Here, we have summarized the function and various ligands of PPAR-γ and have highlighted various miRNAs involved in the regulation of PPAR-γ.

Macrophages in wound healing: activation and plasticity

Macrophages are critically involved in wound healing, from dampening inflammation to clearing cell debris and coordinating tissue repair. Within the wound, the complexity of macrophage function is increasingly recognized, with adverse outcomes when macrophages are inappropriately activated, such as in fibrosis or chronic non-healing wounds. Recent advances in in vivo and translational wound models, macrophage-specific deletions and new technologies to distinguish macrophage subsets, have uncovered the vast spectrum of macrophage activation and effector functions. Here, we summarize the main players in wound-healing macrophage activation and function, including cytokines, apoptotic cells, nucleotides and mechanical stimuli. We highlight recent studies demonstrating cooperation between these factors for optimal wound healing. Next, we describe recent technologies such as cell tracking and single-cell RNA-seq, which have uncovered remarkable plasticity and heterogeneity in blood-derived or tissue-resident macrophages and discuss the implications for wound healing. Lastly, we evaluate macrophage dysfunction in aberrant wound healing that occurs in aging, diabetes and fibrosis. A better understanding of the longevity and plasticity of wound-healing macrophages, and identification of unique macrophage subsets or specific effector molecules in wound healing, would shed light on the therapeutic potential of manipulating macrophage function for optimal wound healing.

Metformin induces the M2 macrophage polarization to accelerate the wound healing via regulating AMPK/mTOR/NLRP3 inflammasome singling pathway

BACKGROUND

Skin wound healing is a challenging problem, especially in aging or diabetic patients, which becomes more difficult to heal, and easily results in considerable public health burden. The purpose of this study was to investigate the effects of metformin on wound healing and explore its underlying mechanism.

METHODS

Metformin was local topical application in rat skin defect models. Alterations in the wounded skin were observed, and angiogenesis in the wound also was analyzed by immunohistochemical staining. The markers associated with differentiation macrophage were analyzed by immunofluorescence staining. The roles of AMPK singling pathway and the relative protein of NLRP3 inflammasome in wound were also analyzed by western blotting. In addition, AMPK/mTOR/NLRP3 inflammasome signaling axis was investigated to further analyze the molecular mechanism of metformin treatment on inducing M2 macrophage polarization in vitro.

RESULTS

Out results showed that metformin improved wound healing and angiogenesis which was paralleled by M2 macrophage polarization. We also found that the level of relative proteins of NLRP3 inflammasome was markedly decreased after metformin treatment. Furthermore, blockage of AMPK or activation of mTOR abolished the effects of metformin treatment on depressing NLRP3 inflammasome activation, M2 polarization and improving wound healing. It suggested that the treatment effects of metformin on wound healing were through regulating AMPK/mTOR/NLRP3 inflammasome signaling axis.

CONCLUSION

Metformin regulated AMPK/mTOR singling pathway to inhibit NLRP3 inflammasome activation, which boosted M2 macrophage polarization to accelerate the wound healing. These findings provided new insights into the molecular mechanism of metformin therapy and its therapeutic potential in wound healing.

Abdominal Panniculectomy: Determining the Impact of Diabetes on Complications and Risk Factors for Adverse Events

BACKGROUND

The prevalence of obesity along with bariatric surgery and massive weight loss requiring panniculectomy is increasing in the United States. The effect of diabetes mellitus on outcomes following panniculectomy remains poorly defined despite its prevalence. This study aims to evaluate the impact of diabetes mellitus on complications following panniculectomy and determine risk factors for adverse events.

METHODS

The American College of Surgeons National Surgical Quality Improvement Program database was used to identify patients undergoing panniculectomy between 2010 and 2015. Patients were stratified based on diabetes status.

RESULTS

Review of the database identified 7035 eligible patients who underwent panniculectomy, of which 770 (10.9 percent) were diabetic. Multivariate regression showed that diabetes mellitus was a significant risk factor for wound dehiscence (OR, 1.92; 95 percent CI, 1.41 to 3.15; p = 0.02). Obesity was a significant risk factor for superficial (OR, 2.78; 95 percent CI, 1.53 to 3.69; p < 0.001) and deep (OR, 1.52; 95 percent CI, 1.38 to 3.97; p = 0.01) incisional surgical-site infection. Smokers were also at an increased risk for superficial (OR, 1.42; 95 percent CI, 1.19 to 1.75; p = 0.03) and deep (OR, 1.63; 95 percent CI, 1.31 to 2.22; p = 0.02) incisional surgical-site infection.

CONCLUSIONS

Diabetes mellitus is an independent risk factor for wound dehiscence following panniculectomy. Obesity and smoking were significant risk factors for superficial and deep incisional surgical-site infection. These results underscore the importance of preoperative risk factor evaluation in patients undergoing panniculectomy for safe outcomes.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, II.

Elevated Local Senescence in Diabetic Wound Healing Is Linked to Pathological Repair via CXCR2

Cellular senescence can be broadly defined as a stable, but essentially irreversible, loss of proliferative capacity. Historically, senescence has been described as a negative outcome of advanced cellular age. It is now clear, however, that senescence represents a dynamic autonomous stress response, integral to long-term tumor suppression. Transient induction of a senescent phenotype has actually been suggested to promote regeneration in both liver and skin. Here, we explored the role of senescence in pathological aged and diabetic murine wound healing. Aged and diabetic wounds had greater numbers of senescent cells, and diabetic macrophages maintained altered retention of polarization and produced a CXCR2-enriched senescence-associated secretory phenotype (i.e., SASP). Of translational relevance, targeted expression of CXCR2 in primary human dermal fibroblasts led to paracrine induction of nuclear p21. Furthermore, a selective agonist to CXCR2 was able to reverse delayed healing in diabetic mice and accelerate ex vivo human skin wound healing. Collectively, these data suggest a hitherto unappreciated role for CXCR2 in mediating cellular senescence in pathological wound repair.

Cytokine production capabilities of human primary monocyte-derived macrophages from patients with diabetes mellitus type 2 with and without diabetic peripheral neuropathy

INTRODUCTION

Monocytes from patients with diabetes mellitus type 2 (DM2) are dysfunctional, persistently primed, and prone to a proinflammatory phenotype. This may alter the phenotype of their differentiation to macrophages and result in diabetic peripheral neuropathy (DPN), nerve damage, nerve sensitization, and chronic pain. We have previously demonstrated that CD163 is a molecule that promotes an anti-inflammatory cellular phenotype in human primary macrophages, but this has not been proven in macrophages from patients with DM2 or DPN. Thus, we hypothesize that macrophages from patients with DM2 or DPN display an altered proinflammatory functional phenotype related to cytokine production and that the induction of CD163 expression will promote a more homeostatic phenotype by reducing their proinflammatory responsiveness.

PATIENTS AND METHODS

We tested these hypotheses in vitro using blood monocyte-derived macrophages from healthy subjects and patients with DM2 with and without DPN. Cells were incubated in the presence or the absence of 5 µg/mL of lipopolysaccharide (LPS). The concentrations of interleukin-10, interleukin-6, tumor necrosis factor-alpha (TNF-α), TGF-β, and monocyte chemoattractant protein-1 (MCP-1) were measured using ELISA assays. Macrophages were transfected with an empty vector plasmid or a plasmid containing the CD163 gene using mannosylated polyethylenimine nanoparticles.

RESULTS

Our results show that nonstimulated DM2 or DPN macrophages have a constitutive primed proinflammatory state and display a deficient production of proinflammatory cytokines upon a proinflammatory challenge when compared to healthy macrophages. CD163 induction produced an anti-inflammatory phenotype in the healthy control group, and this effect was partial in DM2 or DPN macrophages.

CONCLUSION

Our results suggest that diabetic macrophages adopt a complex phenotype that is only partially reversed by CD163 induction. Future experiments are focused on elucidating this differential responsiveness between healthy and diabetic macrophages.

Exercise rescues the immune response fine-tuned impaired by peroxisome proliferator-activated receptors γ deletion in macrophages

BACKGROUND

Exercise is a powerful tool for prevention and treatment of many conditions related to the cardiovascular system and also chronic low-grade inflammation. Peroxisome proliferator-activated receptors γ (PPARγ) exerts an import role on the regulation of metabolic profile and subsequent inflammatory response, especially in macrophages.

PURPOSE

To investigate the effects of 8-week moderate-exercise training on metabolic and inflammatory parameters in mice with PPARγ deficiency in myeloid cells.

METHODS

Twelve-week old mice bearing PPARγ deletion exclusively in myeloid cells (PPARγlox/lox Lys Cre ^-/+ , knockout [KO]) and littermate controls (PPARγlox/lox Lys Cre ^-/- , wild type [WT]) were submitted to 8-week exercise training (treadmill running at moderate intensity, 5 days/week). Animals were evaluated for food intake, glucose homeostasis, serum metabolites, adipose tissue and peritoneal macrophage inflammation, and basal and stimulated cytokine secretion.

RESULTS

Exercise protocol did not improve glucose metabolism or adiponectin concentrations in serum of KO mice. Moreover, the absence of PPARγ in macrophages exacerbated the proinflammatory profile in sedentary mice. Peritoneal cultured cells had higher tumor necrosis factor-α (TNF-α) secretion in nonstimulated and lipopolysaccharide (LPS)-stimulated conditions and higher Toll-4 receptor (TLR4) gene expression under LPS stimulus. Trained mice showed reduced TNF-α content in adipose tissue independently of the genotype. M2 polarization ability was impaired in KO peritoneal macrophages after exercise training, while adipose tissue-associated macrophages did not present any effect by PPARγ ablation.

CONCLUSION

Overall, PPARγ seems necessary to maintain macrophages appropriate response to inflammatory stimulus and macrophage polarization, affecting also whole body lipid metabolism and adiponectin profile. Exercise training showed as an efficient mechanism to restore the immune response impaired by PPARγ deletion in macrophages.

High glucose induces a priming effect in macrophages and exacerbates the production of pro-inflammatory cytokines after a challenge

Introduction

Painful diabetic neuropathy is associated with chronic inflammation, in which macrophages are the key effectors. We utilized an in vitro approach to determine the effects of high glucose on macrophage phenotype.

Materials and methods

We exposed human THP-1 macrophages to normal glucose (5 mM) and a clinically relevant high glucose environment (15 mM) and measured the expression and concentration of molecules associated with a diabetic cellular phenotype.

Results

We found that THP-1 macrophages in high glucose conditions did not influence the basal expression of cyclooxygenase-2, Toll-like receptor-4, or class A scavenger receptor mRNA, or the concentrations of the cytokines interleukin (IL)-6, monocyte chemoattractant protein (MCP)-1, and IL-10, but induced a priming effect on tumor necrosis factor (TNF)-α. Then, we stimulated THP-1 macrophages with a strong pro-inflammatory stimulus lipopolysaccharide (LPS; 5 µg/mL). After stimulation with LPS, we observed an exacerbated increase in TNF-α, IL-6, and MCP-1 concentration in the high glucose condition compared to the normal glucose environment. THP-1 macrophages in high glucose conditions developed tolerance to IL-10 anti-inflammatory effects (TNF-α production) when challenged with LPS.

Conclusion

Our in vitro approach allows the study of macrophages as potential targets for therapeutic purposes since it compares them to primary human macrophages exposed to high glucose and macrophages from patients with diabetes or complications of painful diabetic neuropathy (i.e. ulcers, adipocytes, and pancreas).