Expression and activity of arginase isoenzymes during normal and diabetes-impaired skin repair

Metabolic reprogramming in skin wound healing

Metabolic reprogramming refers to the ability of a cell to alter its metabolism in response to different stimuli and forms of pressure. It helps cells resist external stress and provides them with new functions. Skin wound healing involves the metabolic reprogramming of nutrients, such as glucose, lipids, and amino acids, which play vital roles in the proliferation, differentiation, and migration of multiple cell types. During the glucose metabolic process in wounds, glucose transporters and key enzymes cause elevated metabolite levels. Glucose-mediated oxidative stress drives the proinflammatory response and promotes wound healing. Reprogramming lipid metabolism increases the number of fibroblasts and decreases the number of macrophages. It enhances local neovascularization and improves fibrin stability to promote extracellular matrix remodelling, accelerates wound healing, and reduces scar formation. Reprogramming amino acid metabolism affects wound re-epithelialization, collagen deposition, and angiogenesis. However, comprehensive reviews on the role of metabolic reprogramming in skin wound healing are lacking. Therefore, we have systematically reviewed the metabolic reprogramming of glucose, lipids, and amino acids during skin wound healing. Notably, we identified their targets with potential therapeutic value and elucidated their mechanisms of action.

Retinopathy of prematurity: A review of pathophysiology and signaling pathways

Retinopathy of prematurity (ROP) is a vasoproliferative disorder of the retina and a leading cause of visual impairment and childhood blindness worldwide. The disease is characterized by an early stage of retinal microvascular degeneration, followed by neovascularization that can lead to subsequent retinal detachment and permanent visual loss. Several factors play a key role during the different pathological stages of the disease. Oxidative and nitrosative stress and inflammatory processes are important contributors to the early stage of ROP. Nitric oxide synthase and arginase play important roles in ischemia/reperfusion-induced neurovascular degeneration. Destructive neovascularization is driven by mediators of the hypoxia-inducible factor pathway, such as vascular endothelial growth factor and metabolic factors (succinate). The extracellular matrix is involved in hypoxia-induced retinal neovascularization. Vasorepulsive molecules (semaphorin 3A) intervene preventing the revascularization of the avascular zone. This review focuses on current concepts about signaling pathways and their mediators, involved in the pathogenesis of ROP, highlighting new potentially preventive and therapeutic modalities. A better understanding of the intricate molecular mechanisms underlying the pathogenesis of ROP should allow the development of more effective and targeted therapeutic agents to reduce aberrant vasoproliferation and facilitate physiological retinal vascular development.

Arginase: Biological and Therapeutic Implications in Diabetes Mellitus and Its Complications

Arginase is a ubiquitous enzyme in the urea cycle (UC) that hydrolyzes L-arginine to urea and L-ornithine. Two mammalian arginase isoforms, arginase1 (ARG1) and arginase2 (ARG2), play a vital role in the regulation of β-cell functions, insulin resistance (IR), and vascular complications via modulating L-arginine metabolism, nitric oxide (NO) production, and inflammatory responses as well as oxidative stress. Basic and clinical studies reveal that abnormal alterations of arginase expression and activity are strongly associated with the onset and development of diabetes mellitus (DM) and its complications. As a result, targeting arginase may be a novel and promising approach for DM treatment. An increasing number of arginase inhibitors, including chemical and natural inhibitors, have been developed and shown to protect against the development of DM and its complications. In this review, we discuss the fundamental features of arginase. Next, the regulatory roles and underlying mechanisms of arginase in the pathogenesis and progression of DM and its complications are explored. Furthermore, we review the development and discuss the challenges of arginase inhibitors in treating DM and its related pathologies.

Application of Metal–Organic Framework in Diagnosis and Treatment of Diabetes

Diabetes-related chronic wounds are often accompanied by a poor wound-healing environment such as high glucose, recurrent infections, and inflammation, and standard wound treatments are fairly limited in their ability to heal these wounds. Metal–organic frameworks (MOFs) have been developed to improve therapeutic outcomes due to their ease of engineering, surface functionalization, and therapeutic properties. In this review, we summarize the different synthesis methods of MOFs and conduct a comprehensive review of the latest research progress of MOFs in the treatment of diabetes and its wounds. State-of-the-art in vivo oral hypoglycemic strategies and the in vitro diagnosis of diabetes are enumerated and different antimicrobial strategies (including physical contact, oxidative stress, photothermal, and related ions or ligands) and provascular strategies for the treatment of diabetic wounds are compared. It focuses on the connections and differences between different applications of MOFs as well as possible directions for improvement. Finally, the potential toxicity of MOFs is also an issue that we cannot ignore.

Wound Healing Impairment in Type 2 Diabetes Model of Leptin-Deficient Mice—A Mechanistic Systematic Review

Type II diabetes mellitus (T2DM) is one of the most prevalent diseases in the world, associated with diabetic foot ulcers and impaired wound healing. There is an ongoing need for interventions effective in treating these two problems. Pre-clinical studies in this field rely on adequate animal models. However, producing such a model is near-impossible given the complex and multifactorial pathogenesis of T2DM. A leptin-deficient murine model was developed in 1959 and relies on either dysfunctional leptin (ob/ob) or a leptin receptor (db/db). Though monogenic, this model has been used in hundreds of studies, including diabetic wound healing research. In this study, we systematically summarize data from over one hundred studies, which described the mechanisms underlying wound healing impairment in this model. We briefly review the wound healing dynamics, growth factors’ dysregulation, angiogenesis, inflammation, the function of leptin and insulin, the role of advanced glycation end-products, extracellular matrix abnormalities, stem cells’ dysregulation, and the role of non-coding RNAs. Some studies investigated novel chronic diabetes wound models, based on a leptin-deficient murine model, which was also described. We also discussed the interventions studied in vivo, which passed into human clinical trials. It is our hope that this review will help plan future research.

Wound healing in aged skin exhibits systems-level alterations in cellular composition and cell-cell communication

Delayed and often impaired wound healing in the elderly presents major medical and socioeconomic challenges. A comprehensive understanding of the cellular/molecular changes that shape complex cell-cell communications in aged skin wounds is lacking. Here, we use single-cell RNA sequencing to define the epithelial, fibroblast, immune cell types, and encompassing heterogeneities in young and aged skin during homeostasis and identify major changes in cell compositions, kinetics, and molecular profiles during wound healing. Our comparative study uncovers a more pronounced inflammatory phenotype in aged skin wounds, featuring neutrophil persistence and higher abundance of an inflammatory/glycolytic Arg1^Hi macrophage subset that is more likely to signal to fibroblasts via interleukin (IL)-1 than in young counterparts. We predict systems-level differences in the number, strength, route, and signaling mediators of putative cell-cell communications in young and aged skin wounds. Our study exposes numerous cellular/molecular targets for functional interrogation and provides a hypothesis-generating resource for future wound healing studies.

Epithelial arginase-1 is a key mediator of age-associated delayed healing in vaginal injury

Pelvic organ prolapse is a disorder that substantially affects the quality of life of millions of women worldwide. The greatest risk factors for prolapse are increased parity and older age, with the largest group requiring surgical intervention being post-menopausal women over 65. Due to ineffective healing in the elderly, prolapse recurrence rates following surgery remain high. Therefore, there is an urgent need to elucidate the cellular and molecular drivers of poor healing in pelvic floor dysfunction to allow effective management and even prevention. Recent studies have uncovered the importance of Arginase 1 for modulating effective healing in the skin. We thus employed novel in vitro and in vivo vaginal injury models to determine the specific role of Arginase 1 in age-related vaginal repair. Here we show, for the first time, that aged rat vaginal wounds have reduced Arginase 1 expression and delayed healing. Moreover, direct inhibition of Arginase 1 in human vaginal epithelial cells also led to delayed scratch-wound closure. By contrast, activation of Arginase 1 significantly accelerated healing in aged vaginal wounds in vivo, to rates comparable to those in young animals. Collectively, these findings reveal a new and important role for Arginase 1 in mediating effective vaginal repair. Targeting age-related Arginase 1 deficiency is a potential viable therapeutic strategy to promote vaginal healing and reduce recurrence rate after surgical repair of pelvic organ prolapse.

Arginase Signalling as a Key Player in Chronic Wound Pathophysiology and Healing

Arginase (ARG) represents an important evolutionarily conserved enzyme that is expressed by multiple cell types in the skin. Arg acts as the mediator of the last step of the urea cycle, thus providing protection against excessive ammonia under homeostatic conditions through the production of L-ornithine and urea. L-ornithine represents the intersection point between the ARG-dependent pathways and the urea cycle, therefore contributing to cell detoxification, proliferation and collagen production. The ARG pathways help balance pro- and anti-inflammatory responses in the context of wound healing. However, local and systemic dysfunctionalities of the ARG pathways have been shown to contribute to the hindrance of the healing process and the occurrence of chronic wounds. This review discusses the functions of ARG in macrophages and fibroblasts while detailing the deleterious implications of a malfunctioning ARG enzyme in chronic skin conditions such as leg ulcers. The review also highlights how ARG links with the microbiota and how this impacts on infected chronic wounds. Lastly, the review depicts chronic wound treatments targeting the ARG pathway, alongside future diagnosis and treatment perspectives.

An Epidermal-Specific Role for Arginase1 during Cutaneous Wound Repair

Nonhealing wounds are a major area of unmet clinical need remaining problematic to treat. Improved understanding of prohealing mechanisms is invaluable. The enzyme arginase1 (ARG1) is involved in prohealing responses, with its role in macrophages best characterized. ARG1 is also expressed by keratinocytes; however, ARG1 function in these critical wound repair cells is not understood. We characterized ARG1 expression in keratinocytes during normal cutaneous repair and reveal de novo temporal and spatial expression at the epidermal wound edge. Interestingly, epidermal ARG1 expression was decreased in both human and murine delayed healing wounds. We therefore generated a keratinocyte-specific ARG1-null mouse model (K14-cre;Arg1^fl/fl) to explore arginase function. Wound repair, linked to changes in keratinocyte proliferation, migration, and differentiation, was significantly delayed in K14-cre;Arg1^fl/fl mice. Similarly, using the arginase inhibitor N(omega)-hydroxy-nor-L-arginine, human in vitro and ex vivo models further confirmed this finding, revealing the importance of the downstream polyamine pathway in repair. Indeed, restoring the balance in ARG1 activity through the addition of putrescine proved beneficial in wound closure. In summary, we show that epidermal ARG1 plays, to our knowledge, a previously unreported intrinsic role in cutaneous healing, highlighting epidermal ARG1 and the downstream mediators as potential targets for the therapeutic modulation of wound repair.

What Are Reactive Oxygen Species, Free Radicals, and Oxidative Stress in Skin Diseases?

Oxygen in the atmosphere is a crucial component for life-sustaining aerobic respiration in humans. Approximately 95% of oxygen is consumed as energy and ultimately becomes water; however, the remaining 5% produces metabolites called activated oxygen or reactive oxygen species (ROS), which are extremely reactive. Skin, the largest organ in the human body, is exposed to air pollutants, including diesel exhaust fumes, ultraviolet rays, food, xenobiotics, drugs, and cosmetics, which promote the production of ROS. ROS exacerbate skin aging and inflammation, but also function as regulators of homeostasis in the human body, including epidermal keratinocyte proliferation. Although ROS have been implicated in various skin diseases, the underlying mechanisms have not yet been elucidated. Current knowledge on ROS-related and oxidative stress-related skin diseases from basic research to clinical treatment strategies are discussed herein. This information may be applied to the future treatment of skin diseases through the individual targeting of the ROS generated in each case via their inhibition, capture, or regulation.

Non-invasive metabolic biomarkers for early diagnosis of diabetic nephropathy: Meta-analysis of profiling metabolomics studies

AIM

Diabetic nephropathy (DN) is one of the worst complications of diabetes. Despite a growing number of DN metabolite profiling studies, most studies are suffering from inconsistency in their findings. The main goal of this meta-analysis was to reach to a consensus panel of significantly dysregulated metabolites as potential biomarkers in DN.

DATA SYNTHESIS

To identify the significant dysregulated metabolites, meta-analysis was performed by "vote-counting rank" and "robust rank aggregation" strategies. Bioinformatics analyses were performed to identify the most affected genes and pathways. Among 44 selected studies consisting of 98 metabolite profiles, 17 metabolites (9 up-regulated and 8 down-regulated metabolites), were identified as significant ones by both the meta-analysis strategies (p-value<0.05 and OR>2 or <0.5) and selected as DN metabolite meta-signature. Furthermore, enrichment analyses confirmed the involvement of various effective biological pathways in DN pathogenesis, such as urea cycle, TCA cycle, glycolysis, and amino acid metabolisms. Finally, by performing a meta-analysis over existing time-course studies in DN, the results indicated that lactic acid, hippuric acid, allantoin (in urine), and glutamine (in blood), are the topmost non-invasive early diagnostic biomarkers.

CONCLUSION

The identified metabolites are potentially involved in diabetic nephropathy pathogenesis and could be considered as biomarkers or drug targets in the disease.

PROSPERO REGISTRATION NUMBER

CRD42020197697.

Potential Role of CXCL10 in Monitoring Response to Treatment in Leprosy Patients

The treatment of multibacillary cases of leprosy with multidrug therapy (MDT) comprises 12 doses of a combination of rifampicin, dapsone and clofazimine. Previous studies have described the immunological phenotypic pattern in skin lesions in multibacillary patients. Here, we evaluated the effect of MDT on skin cell phenotype and on the Mycobacterium leprae-specific immune response. An analysis of skin cell phenotype demonstrated a significant decrease in MRS1 (SR-A), CXCL10 (IP-10) and IFNG (IFN-γ) gene and protein expression after MDT release. Patients were randomized according to whether they experienced a reduction in bacillary load after MDT. A reduction in CXCL10 (IP-10) in sera was associated with the absence of a reduction in the bacillary load at release. Although IFN-γ production in response to M. leprae was not affected by MDT, CXCL10 (IP-10) levels in response to M. leprae increased in cells from patients who experienced a reduction in bacillary load after treatment. Together, our results suggest that CXCL10 (IP-10) may be a good marker for monitoring treatment efficacy in multibacillary patients.

The modulation of the burn wound environment by negative pressure wound therapy: Insights from the proteome

Negative pressure wound therapy has been used to promote wound healing in a variety of settings, including as an adjunct to silver-impregnated dressings in the acute management of paediatric burns. Fluid aspirated by the negative pressure wound therapy system represents a potentially insightful research matrix for understanding the burn wound microenvironment and the intervention's biochemical mechanisms of action. The aim of this study was to characterize the proteome of wound fluid collected using negative pressure wound therapy from children with small-area thermal burns. Samples were obtained as part of a randomized controlled trial investigating the clinical efficacy of adjunctive negative pressure wound therapy. They were compared with blister fluid specimens from paediatric burn patients matched according to demographic and injury characteristics. Protein identification and quantification were performed via liquid chromatography tandem mass spectrometry and sequential window acquisition of all theoretical mass spectra data-independent acquisition. Proteins and biological pathways that were unique to or enriched in negative pressure wound therapy fluid samples were evaluated using principal components, partial least squares-discriminant, and gene ontology enrichment analyses. Eight viable samples of negative pressure wound therapy fluid were collected and analyzed with eight matched blister fluid samples. A total of 502 proteins were quantitatively profiled in the negative pressure wound therapy fluid, of which 444 (88.4%) were shared with blister fluid. Several proteins exhibited significant abundance differences between fluid types, with negative pressure wound therapy fluid showing a higher abundance of matrix metalloproteinase-9, arginase-1, low affinity immunoglobulin gamma Fc region receptor III-A, filamin-A, alpha-2-macroglobulin, and hemoglobin subunit alpha. The results lend support to the hypothesis that negative pressure wound therapy augments wound healing through the modulation of factors involved in the inflammatory response, granulation tissue synthesis, and extracellular matrix maintenance. Data are available via ProteomeXchange with identifier PXD023168.

A possible role for inducible arginase isoform (AI) in the pathogenesis of chronic venous leg ulcer

Chronic venous ulcer (CVU) is a major cause of chronic wounds of lower extremities and presents a significant financial and resource burden to health care systems worldwide. Defects in the vasculature, matrix deposition, and re-epithelialization are the main histopathological changes believed to impede healing. Supplementation of the amino acid arginine that plays a crucial role in the interactions that occur during inflammation and wound healing was proven clinically to improve acute wound healing probably through enhancing activity of inducible arginase (AI) locally in the wounds. However, the possible mechanism of arginine action and the potential beneficial effects of AI/arginine in human chronic wounds remain unclear. In the present study, using biopsies, taken under local anesthesia, from adult patients (n = 12, mean age 55 years old) with CVUs in lower extremities, we investigated the correlation between AI distribution in CVUs and the histopathological changes, mainly proliferative and vascular changes. Our results show a distinct spatial distribution of AI along the ulcer in the epidermis and in the dermis with the highest level of expression being at the ulcer edge and the least expression towards the ulcer base. The AI cellular immunoreactivity, enzymatic activity, and protein levels were significantly increased towards the ulcer edge. Interestingly, a similar pattern of expression was encountered in the proliferative and the vascular changes with strong correlations between AI and the proliferative activity and vascular changes. Furthermore, AI cellular distribution was associated with increased proliferative activity, inflammation, and vascular changes. Our findings of differential expression of AI along the CVU base, edge, and nearby surrounding skin and its associations with increased proliferative activity and vascular changes provide further support to the AI implication in CVU pathogenesis. The presence of high levels of AI in the epidermis of chronic wounds may serve as a molecular marker of impaired healing and may provide future targets for therapeutic intervention.

Cellular and physiological upregulation of inducible nitric oxide synthase, arginase, and inducible cyclooxygenase in wound healing

Wound repair is regulated by overlapping cellular, physiological and biochemical events. Prostaglandins and nitric oxide have been a focus for inflammation research particularly since the discovery of their inducible isoforms nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Study of the cellular expression of iNOS and COX-2 and arginase which competes with iNOS for its substrate, in an in vivo model of wound healing could reveal important roles for these enzymes in the physiological progression of wound repair. Adult male rats received full thickness dermal wounds which were harvested at different times. Protein levels and activities of the enzymes were assessed by western blot and biochemical assays respectively. The cellular distribution and the colocalization were assessed by immunostaining. The protein levels and activities of iNOS, arginase, and COX-2 increased only during the inflammatory phase of wound. Immunocytochemistry showed that the three enzymes were coexpressed and the main cellular source was inflammatory cells mainly macrophages. iNOS was induced at the wound site and was the earliest to increase significantly (p < 0.05) for only up to 3 days postwounding. However, arginase and COX-2 significant ( p < 0.05) upregulation started at a later time points and continued for up to 14 days postwounding. Therefore iNOS, compared with arginase and COX-2, showed a temporal difference in expression during wound healing which could be explained by their products being required at different stages of the healing process. The coordinated expression of the three enzymes at different time points could account for the physiological progression of the healing process.

Mechanisms of obesity-induced metabolic and vascular dysfunctions

Obesity has reached epidemic proportions and its prevalence is climbing. Obesity is characterized by hypertrophied adipocytes with a dysregulated adipokine secretion profile, increased recruitment of inflammatory cells, and impaired metabolic homeostasis that eventually results in the development of systemic insulin resistance, a phenotype of type 2 diabetes. Nitric oxide synthase (NOS) is an enzyme that converts L-arginine to nitric oxide (NO), which functions to maintain vascular and adipocyte homeostasis. Arginase is a ureohydrolase enzyme that competes with NOS for L-arginine. Arginase activity/expression is upregulated in obesity, which results in diminished bioavailability of NO, impairing both adipocyte and vascular endothelial cell function. Given the emerging role of NO in the regulation of adipocyte physiology and metabolic capacity, this review explores the interplay between arginase and NO, and their effect on the development of metabolic disorders, cardiovascular diseases, and mitochondrial dysfunction in obesity. A comprehensive understanding of the mechanisms involved in the development of obesity-induced metabolic and vascular dysfunction is necessary for the identification of more effective and tailored therapeutic avenues for their prevention and treatment.

High in situ mRNA levels of IL-22, TFG-β, and ARG-1 in keloid scars

Keloid scars are currently considered a chronic inflammatory process and no longer a benign skin tumor. Keloids are defined as highly inflamed, hyperproliferative pathological scars. Growth factors and cytokines have important functions in the keloid inflammatory etiopathogenesis. The aim of this study was to analyze the in situ expression of cytokines and growth factors in keloid scars in comparison with that in normal scars. Among them, we specifically assessed TGF-β, FGF, IL-33, IL-22, ARG-1, ARG-2, iNOS, VIP, VIP-R1, TAC, and TAC-R1. A total of 98 biopsies were evaluated, including of 53 keloid and 45 normal scars. The age of patients with keloids ranged from 11 to 73 years, with a mean age of 28 years and predominance of the female gender (58.5% of the total patients). Around 64.15% of the patients belonged to the black ethnic group. Evaluated keloids were most commonly located in the earlobe because of ear piercing, representing 73.6% of the cases. We found significantly greater expression of TGF-β, IL-22, and ARG-1 in keloids when compared with that in normal scars. As for IL-33, ARG-2, and VIP-R1, despite the higher number of mRNA copies found in keloids, this difference was not significant. Furthermore, FGF, iNOS, VIP, TAC, and TAC-R1 mRNA levels were not detectable, and therefore these results were inconclusive in this study. Considering these results, understanding the cellular and molecular mechanisms that control the inflammatory response during cutaneous healing may promote the development of strategies to improve the treatment of patients with keloids.

Impaired wound healing in type 1 diabetes is dependent on 5-lipoxygenase products

Type 1 diabetes is associated with systemic low grade inflammation (LGI). We have previously shown that LGI in diabetic mice depends on systemic circulation of leukotriene (LTB₄) which potentiates the toll-like/IL1β receptors response in macrophages. Impaired wound healing is an important co-morbidity in diabetes, and macrophages play a key role in this process. Here, we investigated the role of leukotrienes on monocytes and macrophages phenotype and in the impaired wound healing in diabetic mice. Type 1 diabetes was induced with streptozotocin in 129SvE wild-type (WT) and leukotrienes-deficient 5LO^−/− (5-lipoxygenase knockout) mice. In diabetics, the systemic levels of LTB4, TNF-α, IL-6, IL-10, IL-12 and IFNγ were increased as well as the frequency of pro-inflammatory monocytes (CD11b⁺Ly6C^highLy6G⁻) compared to healthy mice. In diabetic 5LO^−/− mice, these parameters were similar to those in healthy mice. Resident peritoneal macrophages from diabetic WT mice showed a classically activated M1-like phenotype (high Nos2, Stat and Il12 expression, and nitrite levels). Macrophages from diabetic 5LO^−/− mice presented alternatively activated M2-macrophages markers (high Arg1 and Chi3l3 expression and arginase activity) and when stimulated with IL4, enhanced phosphorylated-STAT6. Cutaneous wound healing in diabetic WT mice was impaired, which correlated with the decreased frequency of M2-macrophages (CD45⁺F4/80⁺CD206⁺) in the lesions. In diabetic 5LO^−/− mice, the frequency of M2-macrophages in the wound was similar to that in healthy mice, suggesting that the impaired healing of diabetic mice depends on 5LO products. The inhibition of leukotrienes or antagonism of its receptors could be a therapeutic alternative for diabetic patients with impaired healing.

Arginase: A Multifaceted Enzyme Important in Health and Disease

The arginase enzyme developed in early life forms and was maintained during evolution. As the last step in the urea cycle, arginase cleaves l-arginine to form urea and l-ornithine. The urea cycle provides protection against excess ammonia, while l-ornithine is needed for cell proliferation, collagen formation, and other physiological functions. In mammals, increases in arginase activity have been linked to dysfunction and pathologies of the cardiovascular system, kidney, and central nervous system and also to dysfunction of the immune system and cancer. Two important aspects of the excessive activity of arginase may be involved in diseases. First, overly active arginase can reduce the supply of l-arginine needed for the production of nitric oxide (NO) by NO synthase. Second, too much l-ornithine can lead to structural problems in the vasculature, neuronal toxicity, and abnormal growth of tumor cells. Seminal studies have demonstrated that increased formation of reactive oxygen species and key inflammatory mediators promote this pathological elevation of arginase activity. Here, we review the involvement of arginase in diseases affecting the cardiovascular, renal, and central nervous system and cancer and discuss the value of therapies targeting the elevated activity of arginase.

Histopathological and Inflammatory Features of Chronically Discharging Open Mastoid Cavities: Secondary Analysis of a Randomized Clinical Trial

Importance

Many patients with an open radical mastoid cavity experience therapy-resistant otorrhea. Little is known about the underlying histopathological substrate of unstable cavities and the correlation with treatment failure.

Objective

To study the histopathological and inflammatory features of chronically discharging open radical mastoid cavities and the influence of different treatments.

Design, Setting, and Participants

This secondary analysis of a randomized clinical trial was a histopathology study of tissue samples of a cohort of 30 patients with a chronically discharging open mastoid cavity. Samples were taken from the cavities, which were treated with either honey gel or conventional eardrops in a tertiary center between 2012 and 2013. Tissue staining was performed in May 2014; final computer analysis/correlation studies were performed in June 2016.

Main Outcomes and Measures

Differences of epithelial tissue coverage, infiltration of T cells (CD3, CD4, CD8) and macrophage (CD68, isoenzyme nitric oxide synthase, arginase 1) (sub-)populations, infection status, and the correlation with clinical presentation.

Results

There were 30 patients (24 [80%] male; mean [SD] age, 59 [14] years). Cavities were covered with either stratified squamous (keratinized) epithelium (n = 10), respiratory columnar epithelium (n = 9), or granulation tissue (n = 10). The presence of respiratory epithelium was associated with lower treatment success (posttreatment VAS improvement of 3.1 [95% CI, 0.5 to 5.8] for discomfort and 3.6 [95% CI, 0.2 to 6.9] for otorrhea in the group with granulation tissue coverage vs 4.9 [95% CI, 0.2 to 9.6] and 5.8 [95% CI, -0.1 to 11.6] in the group with squamous [keratinized] epithelium coverage and 1.4 [95% CI, -1.2 to 4.1] and 2.5 [95% CI, -1.3 to 6.2] in the group with respiratory columnar epithelium coverage). In all 3 tissue types of cavity-covering tissues, T-cell infiltrates consisted of helper T cells and cytotoxic T cells, together with a lower number of macrophages. The immunopositivity for isoenzyme nitric oxide synthase and arginase 1 was high and not restricted to a macrophage subpopulation, but seen in various cell types. Inflammatory infiltrations varied strongly in all 3 tissue modalities.

Conclusions and Relevance

Discharging open mastoid cavities can be classified histologically into 3 different types, based on their coverage: squamous epithelium, respiratory epithelium, or granulation tissue. Treatment is less successful in cavities covered with respiratory epithelium, possibly explained by the status of bacterial infection and local immunological differences.

Arginase-II Deficiency Extends Lifespan in Mice

The mitochondrial arginase type II (Arg-II) has been shown to interact with ribosomal protein S6 kinase 1 (S6K1) and mitochondrial p66^Shc and to promote cell senescence, apoptosis and inflammation under pathological conditions. However, the impact of Arg-II on organismal lifespan is not known. In this study, we demonstrate a significant lifespan extension in mice with Arg-II gene deficiency (Arg-II^−/−) as compared to wild type (WT) control animals. This effect is more pronounced in the females than in the males. The gender difference is associated with higher Arg-II expression levels in the females than in the males in skin and heart at both young and old age. Ablation of Arg-II gene significantly reduces the aging marker p16^INK4a levels in these tissues of old female mice, whereas in the male mice this effect of Arg-II deficiency is weaker. In line with this observation, age-associated increases in S6K1 signaling and p66^Shc levels in heart are significantly attenuated in the female Arg-II^−/− mice. In the male mice, only p66^Shc but not S6K1 signaling is reduced. In summary, our study demonstrates that Arg-II may play an important role in the acceleration of aging in mice. Genetic disruption of Arg-II in mouse extends lifespan predominantly in females, which relates to inhibition of S6K1, p66^Shc, and p16^INK4a. Thus, Arg-II may represent a promising target to decelerate aging process and extend lifespan as well as to treat age-related diseases.

Type I Interferon Supports Inducible Nitric Oxide Synthase in Murine Hepatoma Cells and Hepatocytes and during Experimental Acetaminophen-Induced Liver Damage

Cytokine regulation of high-output nitric oxide (NO) derived from inducible NO synthase (iNOS) is critically involved in inflammation biology and host defense. Herein, we set out to characterize the role of type I interferon (IFN) as potential regulator of hepatic iNOS in vitro and in vivo. In this regard, we identified in murine Hepa1-6 hepatoma cells a potent synergism between pro-inflammatory interleukin-β/tumor necrosis factor-α and immunoregulatory IFNβ as detected by analysis of iNOS expression and nitrite release. Upregulation of iNOS by IFNβ coincided with enhanced binding of signal transducer and activator of transcription-1 to a regulatory region at the murine iNOS promoter known to support target gene expression in response to this signaling pathway. Synergistic iNOS induction under the influence of IFNβ was confirmed in alternate murine Hepa56.1D hepatoma cells and primary hepatocytes. To assess iNOS regulation by type I IFN in vivo, murine acetaminophen (APAP)-induced sterile liver inflammation was investigated. In this model of acute liver injury, excessive necroinflammation drives iNOS expression in diverse liver cell types, among others hepatocytes. Herein, we demonstrate impaired iNOS expression in type I IFN receptor-deficient mice which associated with diminished APAP-induced liver damage. Data presented indicate a vital role of type I IFN within the inflamed liver for fine-tuning pathological processes such as overt iNOS expression.

Arginase1 Deficiency in Monocytes/Macrophages Upregulates Inducible Nitric Oxide Synthase To Promote Cutaneous Contact Hypersensitivity

The innate immune components that modulate allergic contact hypersensitivity (CHS) responses are poorly defined. Using human skin from contact dermatitis patients and a mouse model of CHS, we find that hapten allergens disrupt the Arginase1 (Arg1) and inducible NO synthase (iNOS) dynamic in monocytes/macrophages (mono/MΦ), which renders those cells ineffectual in suppressing skin inflammation. Mice lacking Arg1 in MΦ develop increased CHS characterized by elevated ear thickening, mono/MΦ-dominated dermal inflammation, and increased iNOS and IL-6 expression compared with control mice. Treatment of Arg1^flox/flox; LysMCre^+/- mice with a selective NOS inhibitor or knockout of Nos2, encoding iNOS, significantly ameliorates CHS. Our findings suggest a critical role for Arg1 in mono/MΦ in suppressing CHS through dampening Nos2 expression. These results support that increasing Arg1 may be a potential therapeutic avenue in treating allergic contact dermatitis.

Arginase-2, a miR-1299 target, enhances pigmentation in melasma by reducing melanosome degradation via senescence-induced autophagy inhibition

Expression profiles revealed miR-1299 downregulation concomitant with arginase-2 (ARG2) upregulation in hyperpigmented skin of melasma patients. Opposite regulation of tyrosinase and PMEL17 by miR-1299 and inverse relationship between miR-1299 and ARG2 expression denoted a role of miR-1299 in pigmentation with ARG2 as a miR-1299 target. ARG2 overexpression or knock-down in keratinocytes, the main source of ARG2 in epidermis, positively regulated tyrosinase and PMEL17 protein levels, but not mRNA levels or melanosome transfer. ARG2 overexpression in keratinocytes reduced autophagy equivalent to 3-MA, an autophagy inhibitor which also increased tyrosinase and PMEL17 protein levels, whereas ARG2 knock-down induced opposite results. Autophagy inducer rapamycin reduced ARG2-increased tyrosinase and PMEL17 protein levels. Also, autophagy was reduced in late passage-induced senescent keratinocytes showing ARG2 upregulation. ARG2, but not 3-MA, stimulated keratinocyte senescence. These results suggest that ARG2 reduces autophagy in keratinocytes by stimulating cellular senescence, resulting in skin pigmentation by reducing degradation of transferred melanosomes.

Enhanced Activity of the Macrophage M1/M2 Phenotypes and Phenotypic Switch to M1 in Periodontal Infection

BACKGROUND

Macrophages are central players in the pathogenesis of periodontitis. However, the phenotypic switch of macrophage M1/M2 remains uncertain.

METHODS

Adult male mice were divided into periodontitis (P) or control (C) groups. Bone marrow-derived macrophages (BMMs) were stimulated with Porphyromonas gingivalis lipopolysaccharide (LPS). In both the periodontium and serum, macrophage M1 and M2 phenotypes were detected in vivo and in vitro via the following: 1) immunofluorescence; 2) immunohistochemistry; 3) electrochemiluminescence immunoassays; 4) quantitative polymerase chain reaction assays; and 5) enzyme-linked immunosorbent assays. The M1-type markers used included the following: 1) nitric oxide synthase (NOS)-2; 2) tumor necrosis factor-alpha; 3) interleukin (IL)-1β; 4) IL-6; and 5) C-reactive protein. The M2-type markers were as follows: 1) arginase-1; 2) cluster of differentiation (CD) 206; and 3) IL-10.

RESULTS

Compared with the C group, the P group had a 14-fold increase in F4/80(+) NOS2(+) cells and four-fold more F4/80(+) CD206(+) cells with an enhanced NOS2/CD206 ratio in the periodontium (P <0.01). NOS2(-) CD206(+) and dual NOS2(+) CD206(+) macrophages dominated in the C and P groups, respectively. The P group had significantly increased M1- and M2-type cytokines in both the periodontium and serum and also had an enhanced IL-6/IL-10 ratio in the serum (P <0.05). M1-type markers were significantly upregulated at the mRNA level, whereas M2-type markers were downregulated at both the mRNA and protein levels in BMMs after LPS stimulation (P <0.01).

CONCLUSION

Periodontal inflammation is associated with an enhancement of both the M1 and M2 phenotypes of macrophages, in which a phenotypic switch of M2 to M1 might be a critical mechanism in mediating periodontal tissue damage, including alveolar bone loss.

Macrophage Infiltration and Alternative Activation during Wound Healing Promote MEK1-Induced Skin Carcinogenesis

Macrophages are essential for the progression and maintenance of many cancers, but their role during the earliest stages of tumor formation is unclear. To test this, we used a previously described transgenic mouse model of wound-induced skin tumorigenesis, in which expression of constitutively active MEK1 in differentiating epidermal cells results in chronic inflammation (InvEE mice). Upon wounding, the number of epidermal and dermal monocytes and macrophages increased in wild-type and InvEE skin, but the increase was greater, more rapid, and more sustained in InvEE skin. Macrophage ablation reduced tumor incidence. Furthermore, bioluminescent imaging in live mice to monitor macrophage flux at wound sites revealed that macrophage accumulation was predictive of tumor formation; wounds with the greatest number of macrophages at day 5 went on to develop tumors. Gene expression profiling of flow-sorted monocytes, macrophages, and T cells from InvEE and wild-type skin showed that as wound healing progressed, InvEE macrophages altered their phenotype. Throughout wound healing and after wound closure, InvEE macrophages demonstrated sustained upregulation of several markers implicated in alternative macrophage activation including arginase-1 (ARG1) and mannose receptor (CD206). Notably, inhibition of ARG1 activity significantly reduced tumor formation and epidermal proliferation in vivo, whereas addition of L-arginase to cultured keratinocytes stimulated proliferation. We conclude that macrophages play a key role in early, inflammation-mediated skin tumorigenesis, with mechanistic evidence suggesting that ARG1 secretion drives tumor development by stimulating epidermal cell proliferation. These findings highlight the importance of cancer immunotherapies aiming to polarize tumor-associated macrophages toward an antitumor phenotype.

Arginase: an old enzyme with new tricks

Arginase has roots in early life-forms. It converts L-arginine to urea and ornithine. The former provides protection against NH3; the latter serves to stimulate cell growth and other physiological functions. Excessive arginase activity in mammals has been associated with cardiovascular and nervous system dysfunction and disease. Two relevant aspects of this elevated activity may be involved in these disease states. First, excessive arginase activity reduces the supply of L-arginine needed by nitric oxide (NO) synthase to produce NO. Second, excessive production of ornithine leads to vascular structural problems and neural toxicity. Recent research has identified inflammatory agents and reactive oxygen species (ROS) as drivers of this pathologic elevation of arginase activity and expression. We review the involvement of arginase in cardiovascular and nervous system dysfunction, and discuss potential therapeutic interventions targeting excess arginase.

Xanthine Oxidoreductase Function Contributes to Normal Wound Healing

Chronic, nonhealing wounds result in patient morbidity and disability. Reactive oxygen species (ROS) and nitric oxide (NO) are both required for normal wound repair, and derangements of these result in impaired healing. Xanthine oxidoreductase (XOR) has the unique capacity to produce both ROS and NO. We hypothesize that XOR contributes to normal wound healing. Cutaneous wounds were created in C57Bl6 mice. XOR was inhibited with dietary tungsten or allopurinol. Topical hydrogen peroxide (H2O2, 0.15%) or allopurinol (30 μg) was applied to wounds every other day. Wounds were monitored until closure or collected at d 5 to assess XOR expression and activity, cell proliferation and histology. The effects of XOR, nitrite, H2O2 and allopurinol on keratinocyte cell (KC) and endothelial cell (EC) behavior were assessed. We identified XOR expression and activity in the skin and wound edges as well as granulation tissue. Cultured human KCs also expressed XOR. Tungsten significantly inhibited XOR activity and impaired healing with reduced ROS production with reduced angiogenesis and KC proliferation. The expression and activity of other tungsten-sensitive enzymes were minimal in the wound tissues. Oral allopurinol did not reduce XOR activity or alter wound healing but topical allopurinol significantly reduced XOR activity and delayed healing. Topical H2O2 restored wound healing in tungsten-fed mice. In vitro, nitrite and H2O2 both stimulated KC and EC proliferation and EC migration. These studies demonstrate for the first time that XOR is abundant in wounds and participates in normal wound healing through effects on ROS production.

Increased cell proliferation and differential protein expression induced by low-level Er:YAG laser irradiation in human gingival fibroblasts: proteomic analysis

Erbium-doped yttrium aluminum garnet (Er:YAG) laser treatment has demonstrated favorable wound healing effect after periodontal therapy. One of the reasons may be the positive biological effect of the low-level laser on the irradiated tissues, although the mechanism remains unclear. The aim of this study was to investigate the effect of low-level Er:YAG laser irradiation on cell proliferation and laser-induced differential expression of proteins in human gingival fibroblasts (HGFs) by proteomic analysis. In the first experiment, HGFs were exposed to low-level Er:YAG laser irradiation and the laser-induced cell proliferation and damage were evaluated on day 3. In the second experiment, proteomic analysis was performed on day 1 after irradiation. The peptides prepared from HGFs were analyzed by a hybrid ion trap-Fourier transform mass spectrometer, Mascot search engine, and UniProtKB database. A significant increase in cell proliferation without cell damage after irradiation was observed. Among the total identified 377 proteins, 59 proteins, including galectin-7, which was associated with the process of wound healing, were upregulated and 15 proteins were downregulated in laser-treated HGFs. In the third experiment, the increase in messenger RNA (mRNA) and protein expression of galectin-7 in the irradiated HGFs was validated by various analytical techniques. In addition, the effect of recombinant human galectin-7 on the modulation of HGFs proliferation was confirmed. The results indicate that low-level Er:YAG laser irradiation can promote HGF proliferation and induce a significant change in protein expression and the upregulation of galectin-7 expression may partly contribute to the increase in cell proliferation.

Arginase in retinopathy

Ischemic retinopathies, such as diabetic retinopathy (DR), retinopathy of prematurity and retinal vein occlusion are a major cause of blindness in developed nations worldwide. Each of these conditions is associated with early neurovascular dysfunction. However, conventional therapies target clinically significant macula edema or neovascularization, which occur much later. Intra-ocular injections of anti-VEGF show promise in reducing retinal edema, but the effects are usually transient and the need for repeated injections increases the risk of intraocular infection. Laser photocoagulation can control pathological neovascularization, but may impair vision and in some patients the retinopathy continues to progress. Moreover, neither treatment targets early stage disease or promotes repair. This review examines the potential role of the ureahydrolase enzyme arginase as a therapeutic target for the treatment of ischemic retinopathy. Arginase metabolizes l-arginine to form proline, polyamines and glutamate. Excessive arginase activity reduces the l-arginine supply for nitric oxide synthase (NOS), causing it to become uncoupled and produce superoxide and less NO. Superoxide and NO react and form the toxic oxidant peroxynitrite. The catabolic products of polyamine oxidation and glutamate can induce more oxidative stress and DNA damage, both of which can cause cellular injury. Studies indicate that neurovascular injury during retinopathy is associated with increased arginase expression/activity, decreased NO, polyamine oxidation, formation of superoxide and peroxynitrite and dysfunction and injury of both vascular and neural cells. Furthermore, data indicate that the cytosolic isoform arginase I (AI) is involved in hyperglycemia-induced dysfunction and injury of vascular endothelial cells whereas the mitochondrial isoform arginase II (AII) is involved in neurovascular dysfunction and death following hyperoxia exposure. Thus, we postulate that activation of the arginase pathway causes neurovascular injury by uncoupling NOS and inducing polyamine oxidation and glutamate formation, thereby reducing NO and increasing oxidative stress, all of which contribute to the retinopathic process.

Insights into the arginine paradox: evidence against the importance of subcellular location of arginase and eNOS

Reduced production of nitric oxide (NO) is one of the first indications of endothelial dysfunction and precedes overt cardiovascular disease. Increased expression of Arginase has been proposed as a mechanism to account for diminished NO production. Arginases consume l-arginine, the substrate for endothelial nitric oxide synthase (eNOS), and l-arginine depletion is thought to competitively reduce eNOS-derived NO. However, this simple relationship is complicated by the paradox that l-arginine concentrations in endothelial cells remain sufficiently high to support NO synthesis. One mechanism proposed to explain this is compartmentalization of intracellular l-arginine into distinct, poorly interchangeable pools. In the current study, we investigated this concept by targeting eNOS and Arginase to different intracellular locations within COS-7 cells and also BAEC. We found that supplemental l-arginine and l-citrulline dose-dependently increased NO production in a manner independent of the intracellular location of eNOS. Cytosolic arginase I and mitochondrial arginase II reduced eNOS activity equally regardless of where in the cell eNOS was expressed. Similarly, targeting arginase I to disparate regions of the cell did not differentially modify eNOS activity. Arginase-dependent suppression of eNOS activity was reversed by pharmacological inhibitors and absent in a catalytically inactive mutant. Arginase did not directly interact with eNOS, and the metabolic products of arginase or downstream enzymes did not contribute to eNOS inhibition. Cells expressing arginase had significantly lower levels of intracellular l-arginine and higher levels of ornithine. These results suggest that arginases inhibit eNOS activity by depletion of substrate and that the compartmentalization of l-arginine does not play a major role.

Local arginase 1 activity is required for cutaneous wound healing

Chronic nonhealing wounds in the elderly population are associated with a prolonged and excessive inflammatory response, which is widely hypothesized to impede healing. Previous studies have linked alterations in local L-arginine metabolism, principally mediated by the enzymes arginase (Arg) and inducible nitric oxide synthase (iNOS), to pathological wound healing. Over subsequent years, interest in Arg/iNOS has focused on the classical versus alternatively activated (M1/M2) macrophage paradigm. Although the role of iNOS during healing has been studied, Arg contribution to healing remains unclear. Here, we report that Arg is dynamically regulated during acute wound healing. Pharmacological inhibition of local Arg activity directly perturbed healing, as did Tie2-cre-mediated deletion of Arg1, revealing the importance of Arg1 during healing. Inhibition or depletion of Arg did not alter alternatively activated macrophage numbers but instead was associated with increased inflammation, including increased influx of iNOS(+) cells and defects in matrix deposition. Finally, we reveal that in preclinical murine models reduced Arg expression directly correlates with delayed healing, and as such may represent an important future therapeutic target.

Glucose toxic effects on granulation tissue productive cells: the diabetics' impaired healing

Type 2 diabetes mellitus is a metabolic noncommunicable disease with an expanding pandemic magnitude. Diabetes predisposes to lower extremities ulceration and impairs the healing process leading to wound chronification. Diabetes also dismantles innate immunity favoring wound infection. Amputation is therefore acknowledged as one of the disease's complications. Hyperglycemia is the proximal detonator of systemic and local toxic effectors including proinflammation, acute-phase proteins elevation, and spillover of reactive oxygen and nitrogen species. Insulin axis deficiency weakens wounds' anabolism and predisposes to inflammation. The systemic accumulation of advanced glycation end-products irreversibly impairs the entire physiology from cells-to-organs. These factors in concert hamper fibroblasts and endothelial cells proliferation, migration, homing, secretion, and organization of a productive granulation tissue. Diabetic wound bed may turn chronically inflammed, procatabolic, and an additional source of circulating pro-inflammatory cytokines, establishing a self-perpetuating loop. Diabetic fibroblasts and endothelial cells may bear mitochondrial damages becoming prone to apoptosis, which impairs granulation tissue cellularity and perfusion. Endothelial progenitor cells recruitment and tubulogenesis are also impaired. Failure of wound reepithelialization remains a clinical challenge while it appears to be biologically multifactorial. Ulcer prevention by primary care surveillance, education, and attention programs is of outmost importance to reduce worldwide amputation figures.

Arginine plus proline supplementation elicits metabolic adaptation that favors wound healing in diabetic rats

Diabetic patients with wounds are at risk of protein malnutrition, have low arginine plasma levels, and suffer from delayed wound healing. We sought to determine the efficacy of arginine plus proline supplementation on protein and amino acid metabolism and on wound repair in a model of diabetic rats. Eighteen 11-wk-old Zucker diabetic fatty fa/fa male rats underwent a 7-cm abdominal skin incision with implantation of sponges and daily excision of full-thickness round sections of dorsal skin for 5 days. They were randomized to be fed with either a standard formula (S group, Clinutren Iso), a high-protein and arginine (ARG) plus proline (PRO)-enriched formula (ARG+PRO group, Clinutren Repair), or an isonitrogenous isoenergetic control formula (IC group). Nitrogen balance was calculated daily. The rats were euthanized on day 5, and plasma glucose, insulin, amino acids, skin epithelialization, and angiogenesis were measured. In macrophages, we assessed inducible nitric oxide synthase (iNOS) and arginase expression, production of nitric oxide (NO) and amino acid metabolism. Both the ARG+PRO and IC groups showed improved nitrogen balance. ARG plus PRO supplementation increased proline and branched-chain amino acid plasma concentrations and improved angiogenesis. Arginase and iNOS expressions in macrophages were reduced, together with NO and citrulline production. In diabetic rats, ARG plus PRO supplementation improves wound angiogenesis and favors whole body protein metabolism. Low macrophage iNOS expression at day 5 may reflect a low inflammatory state in the wounds, favoring wound closure.

Endothelial dysfunction and diabetes: effects on angiogenesis, vascular remodeling, and wound healing

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by inappropriate hyperglycemia due to lack of or resistance to insulin. Patients with DM are frequently afflicted with ischemic vascular disease or wound healing defect. It is well known that type 2 DM causes amplification of the atherosclerotic process, endothelial cell dysfunction, glycosylation of extracellular matrix proteins, and vascular denervation. These complications ultimately lead to impairment of neovascularization and diabetic wound healing. Therapeutic angiogenesis remains an attractive treatment modality for chronic ischemic disorders including PAD and/or diabetic wound healing. Many experimental studies have identified better approaches for diabetic cardiovascular complications, however, successful clinical translation has been limited possibly due to the narrow therapeutic targets of these agents or the lack of rigorous evaluation of pathology and therapeutic mechanisms in experimental models of disease. This paper discusses the current body of evidence identifying endothelial dysfunction and impaired angiogenesis during diabetes.

The effect of captopril on impaired wound healing in experimental diabetes

We aimed to investigate whether oral administration of captopril modulate wound healing, nitric oxide (NO), and vascular endothelial growth factor (VEGF) concentration in wound fluid of diabetic rats. 48 male Sprague-Dawley rats were divided in four groups (n = 12). The 36 rats were rendered diabetic by streptozotocin. The animals of the first and second groups received 25 and 50 mg/kg/day captopril, respectively, (DM-cap25 and DM-cap50). The animals of the third group were treated by distilled water (DM-control). Control rats had no intervention. The wound fluid level of NO and VEGF were measured. Wound specimens were investigated histopathologically. At the 5th day, there was significantly more NO(x) in wound fluid of DM-cap25 compared to other groups. At the 7th day, both captopril-treated groups had more NO(x) in wound fluid compared to other groups. At the 11th day, both captopril-treated groups had more NO(x) in wound fluid compared to DM-control group. VEGF concentration was significantly higher in both captopril-treated groups versus DM-control group (P < .05). There were significant higher wound healing scores in captopril-treated groups compared with DM-control group (P < .05). These results suggest that captopril might be useful in diabetic wound healing.

Arginase inhibition promotes wound healing in mice

OBJECTIVE

Arginase plays important regulatory roles in polyamine, ornithine, and nitric oxide syntheses. However, its role in the healing process has not been delineated. In this study, we used a highly potent and specific inhibitor of arginase, namely 2(S)-amino-6-boronohexanoic acid NH4 (ABH) to evaluate the role of arginase function in wound healing.

MATERIALS AND METHODS

ABH or saline was applied topically to full thickness, dorsal, excisional wounds in C57BL/6 mice every 8 hours for 14 days post surgery and the rate of wound closure was estimated planimetrically. Wound tissue was harvested from mice sacrificed on postoperative days 3 and 7 and examined histologically. The extent of epithelial, connective, and granulation tissue present within the wound area was estimated histomorphometrically. The effect of ABH on wound arginase activity, production of nitric oxide metabolites (NO(x)), and presence of smooth muscle actin positive cells (myofibroblasts) was evaluated.

RESULTS

While arginase activity was inhibited in vivo, the rate of wound closure significantly increased 7 days post-surgery, (21 ± 4%: P < .01; Student t test) in ABH treated animals. This was accompanied by an early increase in wound granulation tissue and accumulation of NO(x) followed by enhanced re-epithelialization and localization of myofibroblasts beneath the wound epithelium.

CONCLUSION

Arginase inhibition improves excisional wound healing and may be used to develop therapeutics for early wound closure.

Exploring the "hair growth-wound healing connection": anagen phase promotes wound re-epithelialization

When the skin is damaged, a variety of cell types must migrate, proliferate, and differentiate to reform a functional barrier to the external environment. Recent studies have shown that progenitor cells residing in hair follicles (HFs) are able to contribute to this re-epithelialization of wounds in vivo. However, the influence of the hair cycle on wound healing has not previously been addressed. Here, we have exploited spontaneous postnatal hair-cycle synchronicity in mice to systematically examine the influence of the different hair-cycle stages on murine skin wound healing. We report significant acceleration of healing during the anagen phase of HF cycling in vivo, associated with alterations in epithelial, endothelial, and inflammatory cell types. Intriguingly, gene profiling data reveal a clear correlation between the transcription of genes beneficial for wound healing and those upregulated during the anagen phase of the hair cycle in unwounded skin. These findings, which demonstrate a previously unappreciated association between HF cycling and wound healing, reveal numerous molecular correlates for further investigation.

Role of arginine in superficial wound healing in man

Arginine supplementation has been identified as advantageous in experimental wound healing. However, the mechanisms underlying this beneficial effect in tissue repair remain unresolved. Animal studies suggest that the beneficial role of arginine supplementation is mediated, at least in part through NO. The latter component mediates processes involved in tissue repair, including angiogenesis, epithelialization and collagen formation. This prospective study is performed to investigate arginine metabolism in acute surgical wounds in man. Expression of enzymes, known to be involved in arginine metabolism, was studied in donor sites of skin grafts of 10 hospitalized patients undergoing skin transplantation. Plasma and wound fluid levels of arginine metabolites (ornithine, citrulline, nitrate and nitrite = NOx) were measured using High Performance Liquid Chromatography. Expression of iNOS, eNOS, arginase-1 and arginase-2 was studied by immunohistochemistry in paraffin sections of skin tissue. Arginase-1 concentration was measured in plasma and wound fluid using ELISA. Arginase-2 was determined using Western blot analysis. We observed increased levels of citrulline, ornithine, NOx and arginase-1 in wound fluid when compared with plasma. Arginase-2 was expressed in both plasma and wound fluid and seemed higher in plasma. iNOS was expressed by neutrophils, macrophages, fibroblasts, keratinocytes and endothelial cells upon wounding, whereas eNOS reactivity was observed in endothelial cells and fibroblasts. Arginase-1 was expressed in neutrophils post-wounding, while arginase-2 staining was observed in endothelial cells, keratinocytes, fibroblasts, macrophages and neutrophils. For the first time, human data support previous animal studies suggesting arginine metabolism for an NO- as well as arginase-mediated reparation of injured skin.

Endothelium-specific GTP cyclohydrolase I overexpression accelerates refractory wound healing by suppressing oxidative stress in diabetes

Refractory wound is a severe complication that leads to limb amputation in diabetes. Endothelial nitric oxide synthase (eNOS) plays a key role in normal wound repair but is uncoupled in streptozotocin (STZ)-induced type 1 diabetes because of reduced cofactor tetrahydrobiopterin (BH(4)). We tested the hypothesis that overexpression of GTP cyclohydrolase I (GTPCH I), the rate-limiting enzyme for de novo BH(4) synthesis, retards NOS uncoupling and accelerates wound healing in STZ mice. Blood glucose levels were significantly increased in both male endothelium-specific GTPCH I transgenic mice (Tg-GCH; via a tie-2 promoter) and wild-type (WT) littermates 5 days after STZ regimen. A full-thickness excisional wound was created on mouse dorsal skin by a 4-mm punch biopsy. Wound closure was delayed in STZ mice, which was rescued in STZ Tg-GCH mice. Cutaneous BH(4) level was significantly reduced in STZ mice vs. WT mice, which was maintained in STZ Tg-GCH mice. In STZ mice, constitutive NOS (cNOS) activity and nitrite levels were decreased compared with WT mice, paralleled by increased superoxide anion (O(2)(-)) level and inducible NOS (iNOS) activity. In STZ Tg-GCH mice, nitrite level and cNOS activity were potentiated and O(2)(-) level and iNOS activity were suppressed compared with STZ mice. Thus endothelium-specific BH(4) overexpression accelerates wound healing in type 1 diabetic mice by enhancing cNOS activity and suppressing oxidative stress.

Assessment of wound healing in the alloxan-induced diabetic rabbit ear model

The enhancement of diabetic wound healing represents a major clinical challenge to researchers. The challenge faced is to identify a suitable animal model that best represents the human situation. However, the majority of diabetic wound healing models are in rodents and are hindered by rapid contraction and thus do not reflect epithelial cell migration, as seen in the human wound. The alloxan-induced diabetic rabbit model is a cheap, reproducible model and offers the advantage of providing a noncontractile avascular wound bed. This study aimed to compare the effects of acute hyperglycemia in the alloxan model to normal rabbit controls on wound healing, using methods of stereology. Alloxan was administered 7 days prior to surgery. Four full-thickness punch biopsy wounds were created on each ear (n = 4). Wounds were excised at 7 and 14 days and prepared for stereological analysis from Masson's trichrome-stained histological sections. It was noted that the alloxan-treated animals showed an increase in the number of inflammatory cells and fibroblasts at 14 days. In addition, it was noted that the length density of blood vessels was reduced in the alloxan-induced diabetic rabbits, representing a greater radial diffusion distance between vessels and a less efficient network for nutrient exchange. This is the first study to take a stereological approach to defining the effects of diabetes mellitus on wound healing in a noncontractile model.

Identification and characterization of infiltrating macrophages in acetaminophen-induced liver injury

The role of macrophages in the pathogenesis of acetaminophen (APAP)-induced liver injury remains controversial, as it has been demonstrated that these cells display pro-toxicant and hepato-protective functions. This controversy may stem from the heterogeneity and/or plasticity of macrophages and the difficulty in distinguishing and differentially studying subpopulations of macrophages in the liver. In the present study, using flow cytometric analysis and fluorescence-labeled antibodies against specific cell surface macrophage markers, we were able to, for the first time, identify an APAP-induced macrophage (IM) population distinct from resident Kupffer cells. The data demonstrated that the IMs were derived from circulating monocytes that infiltrated the liver following APAP-induced liver injury. The IMs exhibited a phenotype consistent with that of alternatively activated macrophages and demonstrated the ability to phagocytize apoptotic cells and induce apoptosis of neutrophils. Furthermore, in the absence of the IMs, the resolution of hepatic damage following APAP-induced hepatotoxicity was delayed in CCR2(-/-) mice compared with wild-type mice. These findings likely contribute to the role of the IMs in the processes of tissue repair, including counteracting inflammation and promoting angiogenesis. The present study also demonstrated the ability of separating populations of macrophages and delineating distinct functions of each group in future studies of inflammatory disease in the liver and other tissues.

Endogenous interferon-gamma is required for efficient skeletal muscle regeneration

The inflammatory response is thought to play important roles in tissue healing. The hypothesis of this study was that the inflammatory cytokine interferon (IFN)-gamma is produced endogenously following skeletal muscle injury and promotes efficient healing. We show that IFN-gamma is expressed at both mRNA and protein levels in skeletal muscle following injury, and that the time course of IFN-gamma expression correlated with the accumulation of macrophages, T-cells, and natural killer cells, as well as myoblasts, in damaged muscle. Cells of each type were isolated from injured muscle, and IFN-gamma expression was detected in each cell type. We also demonstrate that administration of an IFN-gamma receptor blocking antibody to wild-type mice impaired induction of interferon response factor-1, reduced cell proliferation, and decreased formation of regenerating fibers. IFN-gamma null mice showed similarly impaired muscle healing associated with impaired macrophage function and development of fibrosis. In vitro studies demonstrated that IFN-gamma and its receptor are expressed in the C2C12 muscle cell line, and that the IFN-gamma receptor blocking antibody reduced proliferation and fusion of these muscle cells. In summary, our results indicate that IFN-gamma promotes muscle healing, in part, by stimulating formation of new muscle fibers.

Cocoa flavanols lower vascular arginase activity in human endothelial cells in vitro and in erythrocytes in vivo

The availability of l-arginine can be a rate-limiting factor for cellular NO production by nitric oxide synthases (NOS). Arginase competes with NOS for l-arginine as the common substrate. Increased arginase activity has been linked to low NO levels, and an inhibition of arginase activity has been reported to improve endothelium-dependent vasorelaxation. Based on the above, we hypothesized that an increase in the circulating NO pool following flavanol consumption could be correlated with decreased arginase activity. To test this hypothesis we (a) investigated the effects of (-)-epicatechin and its structurally related metabolites on endothelial arginase expression and activity in vitro; (b) evaluated the effects of dietary flavanol-rich cocoa on kidney arginase activity in vivo; and (c) assessed human erythrocyte arginase activity following flavanol-rich cocoa beverage consumption in a double-blind intervention study with cross-over design. The results demonstrate that cocoa flavanols lower arginase-2 mRNA expression and activity in HUVEC. Dietary intervention with flavanol-rich cocoa caused diminished arginase activity in rat kidney and, erythrocyte arginase activity was lowered in healthy humans following consumption of a high flavanol beverage in vivo.

Pros and cons of L-arginine supplementation in disease

The amino acid arginine and one of its metabolites NO have gathered broad attention in the last decade. Although arginine is regarded as a conditionally essential amino acid in disease, L-arginine supplementation in severe illness has not found its way into clinical practice. This might be due to the invalid interpretation of results from studies with immune-enhancing diets containing L-arginine amongst other pharmaconutrients. However, not much attention is given to research using L-arginine as a monotherapy and the possibility of the alternative hypothesis: that L-arginine supplementation is beneficial in disease. The present review will discuss data from studies in healthy and diseased animals and patients with monotherapy of L-arginine to come to an objective overview of positive and negative aspects of L-arginine supplementation in disease with special emphasis on sepsis, cancer, liver failure and wound healing.

Arginase: a critical regulator of nitric oxide synthesis and vascular function

1. Arginase is the focal enzyme of the urea cycle hydrolysing L-arginine to urea and L-ornithine. Emerging studies have identified arginase in the vasculature and have implicated this enzyme in the regulation of nitric oxide (NO) synthesis and the development of vascular disease. 2. Arginase inhibits the production of NO via several potential mechanisms, including competition with NO synthase (NOS) for the substrate L-arginine, uncoupling of NOS resulting in the generation of the NO scavenger, superoxide and peroxynitrite, repression of the translation and stability of inducible NOS protein, inhibition of inducible NOS activity via the generation of urea and by sensitization of NOS to its endogenous inhibitor asymmetric dimethyl-L-arginine. 3. Upregulation of arginase inhibits endothelial NOS-mediated NO synthesis and may contribute to endothelial dysfunction in hypertension, ageing, ischaemia-reperfusion and diabetes. 4. Arginase also redirects the metabolism of L-arginine to L-ornithine and the formation of polyamines and L-proline, which are essential for smooth muscle cell growth and collagen synthesis. Therefore, the induction of arginase may also promote aberrant vessel wall remodelling and neointima formation. 5. Arginase represents a promising novel therapeutic target that may reverse endothelial and smooth muscle cell dysfunction and prevent vascular disease.

The role of endothelial dysfunction in the pathogenesis of impaired diabetic wound healing: a novel therapeutic target?

The global burden of diabetes is attributed to its multiple associated complications including impaired wound healing which can ultimately result in amputation. Peripheral vascular disease, infection, neuropathy and abnormal local cellular and cytokine activity are some of the traditionally cited pathological instigators of defective diabetic wound repair. Despite intensive research and subsequent advances in diabetic wound care technology a single treatment with measurable clinical impact has yet to be determined. The phenomenon of endothelial dysfunction as seen in atherosclerosis and recently identified as a characteristic of diabetic vasculature may contribute to impaired cutaneous healing in this group. Indicators of endothelial dysfunction have been demonstrated in diabetic wounds by a number of investigators. Successful results are being obtained with modifiers of endothelial function in the management of cardiovascular disease. We hypothesise that endothelial dysfunction plays a substantial contributory role in the pathogenesis of wound healing impairment of diabetes and holds potential as a target for therapeutic intervention.