Neurogenic factors in the impaired healing of diabetic foot ulcers

Global trends in publications regarding macrophages-related diabetic foot ulcers in the last two decades

BACKGROUND

Diabetic foot ulcers (DFUs) are one of the most severe and popular complications of diabetes. The persistent non-healing of DFUs is the leading cause of ampu-tation, which causes significant mental and financial stress to patients and their families. Macrophages are critical cells in wound healing and perform essential roles in all phases of wound healing. However, no studies have been carried out to systematically illustrate this area from a scientometric point of view. Although there have been some bibliometric studies on diabetes, reports focusing on the investigation of macrophages in DFUs are lacking.

AIM

To perform a bibliometric analysis to systematically assess the current state of research on macrophage-related DFUs.

METHODS

The publications of macrophage-related DFUs from January 1, 2004, to December 31, 2023, were retrieved from the Web of Science Core Collection on January 9, 2024. Four different analytical tools: VOSviewer (v1.6.19), CiteSpace (v6.2.R4), HistCite (v12.03.07), and Excel 2021 were used for the scientometric research.

RESULTS

A total of 330 articles on macrophage-related DFUs were retrieved. The most published countries, institutions, journals, and authors in this field were China, Shanghai Jiao Tong University of China, Wound Repair and Regeneration, and Aristidis Veves. Through the analysis of keyword co-occurrence networks, historical direct citation networks, thematic maps, and trend topics maps, we synthesized the prevailing research hotspots and emerging trends in this field.

CONCLUSION

Our bibliometric analysis provides a comprehensive overview of macrophage-related DFUs research and insights into promising upcoming research.

The role of FGF-21 in promoting diabetic wound healing by modulating high glucose-induced inflammation

Background

Wound healing is a complex biological process that can be impaired in individuals with diabetes. Diabetic wounds are a serious complication of diabetes that require promoting diagnosis and effective treatment. FGF-21, a member of the endocrine FGF factors family, has caught the spotlight in the treatment of diabetes for its beneficial effects on accelerating human glucose uptake and fat catabolism. However, the therapeutic efficacy of FGF-21 in promoting diabetic wounds remains unknown. This study aims to evaluate the therapeutic potential of FGF-21 in promoting diabetic wound healing.

Methods

we investigated the effects of FGF-21 on wound healing related-cells under high-glucose conditions using various assays such as CCK8, scratch assay, flow cytometry analysis, endothelial tube-formation assay, and transmission electron microscopy. Furthermore, we used db/db mice to verify the healing-promoting therapeutic effects of FGF-21 on diabetic wounds. We also conducted qRT-PCR, Western blot, and immunofluorescence staining analyses to elucidate the underlying mechanism.

Result

Our results indicate that FGF-21 treatment restored hyperglycemic damage on endothelial cell proliferation, migration, and tube-forming ability. It also reduced endothelial cell death rates under high-glucose conditions. TEM analysis showed that FGF-21 treatment effectively restored mitochondrial damage and morphological changes in endothelial cells caused by glucose. Additionally, qRT-PCR and Western blot analysis indicated that FGF-21 treatment restored inflammatory responses caused by hyperglycemic damage. Animal experiments confirmed these findings, suggesting that FGF-21 may be a promising candidate for the treatment of non-healing diabetic wounds due to its effectiveness in stimulating angiogenesis and anti-inflammatory function.

Conclusion

Our study provides evidence that FGF-21 is an essential regulator of wound-related cells under high-glucose conditions and has the potential to be a novel therapeutic target for accelerating diabetic wound healing.

Host-Microbiome Crosstalk in Chronic Wound Healing

The pathogenesis of chronic wounds (CW) involves a multifaceted interplay of biochemical, immunological, hematological, and microbiological interactions. Biofilm development is a significant virulence trait which enhances microbial survival and pathogenicity and has various implications on the development and management of CW. Biofilms induce a prolonged suboptimal inflammation in the wound microenvironment, associated with delayed healing. The composition of wound fluid (WF) adds more complexity to the subject, with proven pro-inflammatory properties and an intricate crosstalk among cytokines, chemokines, microRNAs, proteases, growth factors, and ECM components. One approach to achieve information on the mechanisms of disease progression and therapeutic response is the use of multiple high-throughput 'OMIC' modalities (genomic, proteomic, lipidomic, metabolomic assays), facilitating the discovery of potential biomarkers for wound healing, which may represent a breakthrough in this field and a major help in addressing delayed wound healing. In this review article, we aim to summarize the current progress achieved in host-microbiome crosstalk in the spectrum of CW healing and highlight future innovative strategies to boost the host immune response against infections, focusing on the interaction between pathogens and their hosts (for instance, by harnessing microorganisms like probiotics), which may serve as the prospective advancement of vaccines and treatments against infections.

Clinical practice recommendations for infectious disease management of diabetic foot infection (DFI) - 2023 SPILF

In march 2020, the International Working Group on the Diabetic Foot (IWGDF) published an update of the 2015 guidelines on the diagnosis and management of diabetic foot infection (DFI). While we (the French ID society, SPILF) endorsed some of these recommendations, we wanted to update our own 2006 guidelines and specifically provide informative elements on modalities of microbiological diagnosis and antibiotic treatment (especially first- and second-line regiments, oral switch and duration). The recommendations put forward in the present guidelines are addressed to healthcare professionals managing patients with DFI and more specifically focused on infectious disease management of this type of infection, which clearly needs a multidisciplinary approach. Staging of the severity of the infection is mandatory using the classification drawn up by the IWGDF. Microbiological samples should be taken only in the event of clinical signs suggesting infection in accordance with a strict preliminarily established protocol. Empirical antibiotic therapy should be chosen according to the IWGDF grade of infection and duration of the wound, but must always cover methicillin-sensitive Staphylococcus aureus. Early reevaluation of the patient is a fundamental step, and duration of antibiotic therapy can be shortened in many situations. When osteomyelitis is suspected, standard foot radiograph is the first-line imagery examination and a bone biopsy should be performed for microbiological documentation. Histological analysis of the bone sample is no longer recommended. High dosages of antibiotics are recommended in cases of confirmed osteomyelitis.

Tachykinins Play a Major Role in Micro and Macrovascular Complications in Type 2 Diabetes Patients

Diabetes Mellitus is a metabolic disorder, which is characterized by an increase in blood glucose levels. The defects in the secretion or action of insulin are the major cause of diabetes. Increase in the blood glucose level exerts a negative effect on the normal functions of the body organs and this leads to the dysfunctions of cells and tissue and causes vascular complications in diabetic patients. Several studies indicate that neuropeptides are released from the neurosensory cells which are mainly known as tachykinins which provoke major vascular complications in diabetic patients. Tachykinins are known as pro-inflammatory peptides which increase vascular complications and vascular permeability. The duration and severity of diabetes disease increase the risk of vascular complication in patients. The aim of this review is to elaborate the role of tachykinins in microvascular and macrovascular complications in diabetic patients. The study concluded that tachykinins increase micro and macrovascular complications in diabetic patients.

Healing profiles in patients with a chronic diabetic foot ulcer: An exploratory study with machine learning

Diabetic foot ulcers (DFU) are one of the most frequent and debilitating complications of diabetes. DFU wound healing is a highly complex process, resulting in significant medical, economic and social challenges. Therefore, early identification of patients with a high-risk profile would be important to adequate treatment and more successful health outcomes. This study explores risk assessment profiles for DFU healing and healing prognosis, using machine learning predictive approaches and decision tree algorithms. Patients were evaluated at baseline (T0; N = 158) and 2 months later (T1; N = 108) on sociodemographic, clinical, biochemical and psychological variables. The performance evaluation of the models comprised F1-score, accuracy, precision and recall. Only profiles with F1-score >0.7 were selected for analysis. According to the two profiles generated for DFU healing, the most important predictive factors were illness representations on T1 IPQ-B (IPQ-B ≤ 9.5 and < 10.5) and the DFU duration (≤ 13 weeks). The two predictive models for DFU healing prognosis suggest that biochemical factors are the best predictors of a favorable healing prognosis, namely IL-6, microRNA-146a-5p and PECAM-1 at T0 and angiopoietin-2 at T1. Illness perception at T0 (IPQ-B ≤ 39.5) also emerged as a relevant predictor for healing prognosis. The results emphasize the importance of DFU duration, illness perception and biochemical markers as predictors of  healing in chronic DFUs. Future research is needed to confirm and test the obtained predictive models.

Photocatalytic oxygen evolution and antibacterial biomimetic repair membrane for diabetes wound repair via HIF1-α pathway

Diabetic wounds always have puzzled patients and caused serious social problems. Due to the lack of local blood vessels, severe hypoxia is generated in the defect area, which is an essential reason for the difficulty of wound healing. We have constructed a photocatalytic oxygen evolution and antibacterial biomimetic repair membrane to solve the problems of wound repair. A scanning electron microscope and transmission electron microscope characterized the biomimetic repair membrane. The oxygen evolution of the biomimetic membrane was tested by an oxygen meter. The excellent antibacterial performance of the biomimetic repair membrane was also verified by co-culture with Staphylococcus aureus and Escherichia coli. It was confirmed that the expression of collagen and HIF1-α in fibroblasts was significantly increased in vitro. And the mitochondrial activity of the vascular and nerve was increased considerably. In vivo, the healing time of diabetes wounds treated with the biomimetic repair membrane was significantly reduced, the collagen and the number of pores were increased considerably, and vascular regeneration was enhanced. The biomimetic repair membrane has an excellent performance in photocatalytic oxygen evolution and antibacterial and can significantly promote the repair of diabetes wounds. This will provide a promising treatment for diabetes wound repair.

Therapeutic role of growth factors in treating diabetic wound

Wounds in diabetic patients, especially diabetic foot ulcers, are more difficult to heal compared with normal wounds and can easily deteriorate, leading to amputation. Common treatments cannot heal diabetic wounds or control their many complications. Growth factors are found to play important roles in regulating complex diabetic wound healing. Different growth factors such as transforming growth factor beta 1, insulin-like growth factor, and vascular endothelial growth factor play different roles in diabetic wound healing. This implies that a therapeutic modality modulating different growth factors to suit wound healing can significantly improve the treatment of diabetic wounds. Further, some current treatments have been shown to promote the healing of diabetic wounds by modulating specific growth factors. The purpose of this study was to discuss the role played by each growth factor in therapeutic approaches so as to stimulate further therapeutic thinking.

The neuropeptide substance P/neurokinin-1 receptor system and diabetes: From mechanism to therapy

Diabetes is a significant public health issue known as the world's fastest-growing disease condition. It is characterized by persistent hyperglycemia and subsequent chronic complications leading to organ dysfunction and, ultimately, the failure of target organs. Substance P (SP) is an undecapeptide that belongs to the family of tachykinin (TK) peptides. The SP-mediated activation of the neurokinin 1 receptor (NK1R) regulates many pathophysiological processes in the body. There is also a relation between the SP/NK1R system and diabetic processes. Importantly, deregulated expression of SP has been reported in diabetes and diabetes-associated chronic complications. SP can induce both diabetogenic and antidiabetogenic effects and thus affect the pathology of diabetes destructively or protectively. Here, we review the current knowledge of the functional relevance of the SP/NK1R system in diabetes pathogenesis and its exploitation for diabetes therapy. A comprehensive understanding of the role of the SP/NK1R system in diabetes is expected to shed further light on developing new therapeutic possibilities for diabetes and its associated chronic conditions.

Cutaneous innervation in impaired diabetic wound healing

Type 2 diabetes is associated with several potential comorbidities, among them impaired wound healing, chronic ulcerations, and the requirement for lower extremity amputation. Disease-associated abnormal cellular responses, infection, immunological and microvascular dysfunction, and peripheral neuropathy are implicated in the pathogenesis of the wound healing impairment and the diabetic foot ulcer. The skin houses a dense network of sensory nerve afferents and nerve-derived modulators, which communicate with epidermal keratinocytes and dermal fibroblasts bidirectionally to effect normal wound healing after trauma. However, the mechanisms through which cutaneous innervation modulates wound healing are poorly understood, especially in humans. Better understanding of these mechanisms may provide the basis for targeted treatments for chronic diabetic wounds. This review provides an overview of wound healing pathophysiology with a focus on neural involvement in normal and diabetic wound healing, as well as future therapeutic perspectives to address the unmet needs of diabetic patients with chronic wounds.

Biofilms in Diabetic Foot Ulcers: Significance and Clinical Relevance

Foot infections are the main disabling complication in patients with diabetes mellitus. These infections can lead to lower-limb amputation, increasing mortality and decreasing the quality of life. Biofilm formation is an important pathophysiology step in diabetic foot ulcers (DFU)-it plays a main role in the disease progression and chronicity of the lesion, the development of antibiotic resistance, and makes wound healing difficult to treat. The main problem is the difficulty in distinguishing between infection and colonization in DFU. The bacteria present in DFU are organized into functionally equivalent pathogroups that allow for close interactions between the bacteria within the biofilm. Consequently, some bacterial species that alone would be considered non-pathogenic, or incapable of maintaining a chronic infection, could co-aggregate symbiotically in a pathogenic biofilm and act synergistically to cause a chronic infection. In this review, we discuss current knowledge on biofilm formation, its presence in DFU, how the diabetic environment affects biofilm formation and its regulation, and the clinical implications.

Mechanistic Actions of microRNAs in Diabetic Wound Healing

Wound healing is a complex biological process that is impaired under diabetes conditions. Chronic non-healing wounds in diabetes are some of the most expensive healthcare expenditures worldwide. Early diagnosis and efficacious treatment strategies are needed. microRNAs (miRNAs), a class of 18-25 nucleotide long RNAs, are important regulatory molecules involved in gene expression regulation and in the repression of translation, controlling protein expression in health and disease. Recently, miRNAs have emerged as critical players in impaired wound healing and could be targets for potential therapies for non-healing wounds. Here, we review and discuss the mechanistic background of miRNA actions in chronic wounds that can shed the light on their utilization as specific wound healing biomarkers.

Major Improvement in Wound Healing Through Pharmacologic Mobilization of Stem Cells in Severely Diabetic Rats

Current therapeutic strategies for diabetic foot ulcer (DFU) have focused on developing topical healing agents, but few agents have controlled prospective data to support their effectiveness in promoting wound healing. We tested a stem cell mobilizing therapy for DFU using a combination of AMD3100 and low-dose FK506 (tacrolimus) (AF) in streptozocin-induced type 1 diabetic (T1DM) rats and type 2 diabetic Goto-Kakizaki (GK) rats that had developed peripheral artery disease and neuropathy. Here, we show that the time for healing back wounds in T1DM rats was reduced from 27 to 19 days, and the foot wound healing time was reduced from 25 to 20 days by treatment with AF (subcutaneously, every other day). Similarly, in GK rats treated with AF, the healing time on back wounds was reduced from 26 to 21 days. Further, this shortened healing time was accompanied by reduced scar and by regeneration of hair follicles. We found that AF therapy mobilized and recruited bone marrow-derived CD133⁺ and CD34⁺ endothelial progenitor cells and Ym1/2⁺ M2 macrophages into the wound sites, associated with enhanced capillary and hair follicle neogenesis. Moreover, AF therapy improved microcirculation in diabetic and neuropathic feet in GK rats. This study provides a novel systemic therapy for healing DFU.

Stimulating ideas for heart regeneration: the future of nerve-directed heart therapy

Ischemic heart disease is the leading cause of death worldwide. The blockade of coronary arteries limits oxygen-rich blood to the heart and consequently there is cardiomyocyte (CM) cell death, inflammation, fibrotic scarring, and myocardial remodeling. Unfortunately, current therapeutics fail to effectively replace the lost cardiomyocytes or prevent fibrotic scarring, which results in reduced cardiac function and the development of heart failure (HF) in the adult mammalian heart. In contrast, neonatal mice are capable of regenerating their hearts following injury. However, this regenerative response is restricted to the first week of post-natal development. Recently, we identified that cholinergic nerve signaling is necessary for the neonatal mouse cardiac regenerative response. This demonstrates that cholinergic nerve stimulation holds significant potential as a bioelectronic therapeutic tool for heart disease. However, the mechanisms of nerve directed regeneration in the heart remain undetermined. In this review, we will describe the historical evidence of nerve function during regeneration across species. Specifically, we will focus on the emerging role of cholinergic innervation in modulating cardiomyocyte proliferation and inflammation during heart regeneration. Understanding the role of nerves in mammalian heart regeneration and adult cardiac remodeling can provide us with innovative bioelectronic-based therapeutic approaches for treatment of human heart disease.

Molecular Concept of Diabetic Wound Healing: Effective Role of Herbal Remedies

The incidence of diabetes mellitus (DM) is on the rise, worldwide. One of the main complications in DM is delayed wound healing and it often requires amputation. Various drugs were used to treat DM but they presented with adverse effects. Often, patients failed to comply with such treatment. This opened the door for complementary and alternative medicine. In the present review, we explored the molecular concept of wound healing occurring in different stages with special emphasis to DM. We also highlighted the potential herbal products such as NF3 (Chinese 2-Herb Formula), Zicao, Jing Wan Hong ointment, Aleo vera, mixture of Adiantum capillus-veneris, Commiphora molmol, Aloe vera, and henna, Phenol-rich compound sweet gel, Jinchuang ointment, San-huang-sheng-fu (S) oil, Yi Bu A Jie extract, Astragali Radix (AR) and Rehmanniae Radix (RR), Yiqi Huayu, Tangzu yuyang ointment, Shengji Huayu recipe, Angelica sinensis, Lithospermun erythrorhison, Hippophae rhamnoides L., Curcuma longa and Momordica charantia that could be used effectively to treat DM wounds. Future clinical trials are needed for designing potential drugs which may be effective in treating DM wounds.

Role of biomarkers in predicting diabetes complications with special reference to diabetic foot ulcers

Diabetic foot ulcer (DFU) is one of the major complications of diabetes and about 1% of people with diabetes have to go for lower limb amputation. With better understanding of the pathological basis of DFU, number of biomarkers like atrial natriuretic peptides, galectin-3, and cardiac troponins for diabetic cardiomyopathy, cystatin C for diabetics nephropathy and C-reactive protein for infection and procalcitonin could aid in early and noninvasive diagnosis especially when clinical signs are misleading. Predictive role of novel biomarkers in primary prevention however, requires additional studies considering sex, age and multiple complications in DFU. The current review provides an insight about the novel and emerging biomarkers of diabetes and its complications with special reference to DFUs.

Mast Cells Regulate Wound Healing in Diabetes

Diabetic foot ulceration is a severe complication of diabetes that lacks effective treatment. Mast cells (MCs) contribute to wound healing, but their role in diabetes skin complications is poorly understood. Here we show that the number of degranulated MCs is increased in unwounded forearm and foot skin of patients with diabetes and in unwounded dorsal skin of diabetic mice (P < 0.05). Conversely, postwounding MC degranulation increases in nondiabetic mice, but not in diabetic mice. Pretreatment with the MC degranulation inhibitor disodium cromoglycate rescues diabetes-associated wound-healing impairment in mice and shifts macrophages to the regenerative M2 phenotype (P < 0.05). Nevertheless, nondiabetic and diabetic mice deficient in MCs have delayed wound healing compared with their wild-type (WT) controls, implying that some MC mediator is needed for proper healing. MCs are a major source of vascular endothelial growth factor (VEGF) in mouse skin, but the level of VEGF is reduced in diabetic mouse skin, and its release from human MCs is reduced in hyperglycemic conditions. Topical treatment with the MC trigger substance P does not affect wound healing in MC-deficient mice, but improves it in WT mice. In conclusion, the presence of nondegranulated MCs in unwounded skin is required for proper wound healing, and therapies inhibiting MC degranulation could improve wound healing in diabetes.

To cross-link or not to cross-link? Cross-linking associated foreign body response of collagen-based devices

Collagen-based devices, in various physical conformations, are extensively used for tissue engineering and regenerative medicine applications. Given that the natural cross-linking pathway of collagen does not occur in vitro, chemical, physical, and biological cross-linking methods have been assessed over the years to control mechanical stability, degradation rate, and immunogenicity of the device upon implantation. Although in vitro data demonstrate that mechanical properties and degradation rate can be accurately controlled as a function of the cross-linking method utilized, preclinical and clinical data indicate that cross-linking methods employed may have adverse effects on host response, especially when potent cross-linking methods are employed. Experimental data suggest that more suitable cross-linking methods should be developed to achieve a balance between stability and functional remodeling.

Preclinical and clinical evidence for stem cell therapies as treatment for diabetic wounds

Diabetic wounds remain a global unsolved problem and the cost of diabetes-related amputations and diabetic wound treatment is approximately US$3 billion and US$9 billion per year, respectively. Diabetic foot ulcers (DFUs) occur in 15% of all patients with diabetes and precede 84% of all diabetes-related lower leg amputations. Currently, there is no satisfying treatment for these hard-to-heal-wounds. However, as we discuss here, experimental preclinical evidence for the successful use of adult stem cell therapies for diabetic wounds gives new hope for the development of effective treatments for use in the clinic.

Dynamic Role of Host Stress Responses in Modulating the Cutaneous Microbiome: Implications for Wound Healing and Infection

Significance: Humans are under constant bombardment by various stressors, including psychological anxiety and physiologic injury. Understanding how these stress responses influence the innate immune system and the skin microbiome remains elusive due to the complexity of the neuroimmune and stress response pathways. Both animal and human studies have provided critical information upon which to further elucidate the mechanisms by which mammalian stressors impair normal wound healing and/or promote chronic wound progression. Recent Advances: Development of high-throughput genomic and bioinformatic approaches has led to the discovery of both an epidermal and dermal microbiome with distinct characteristics. This technology is now being used to identify statistical correlations between specific microbiota profiles and clinical outcomes related to cutaneous wound healing and the response to pathogenic infection. Studies have also identified more prominent roles for typical skin commensal organisms in maintaining homeostasis and modulating inflammatory responses. Critical Issues: It is well-established that stress-induced factors, including catecholamines, acetylcholine, and glucocorticoids, increase the risk of impaired wound healing and susceptibility to infection. Despite the characterization of the cutaneous microbiome, little is known regarding the impact of these stress-induced molecules on the development and evolution of the cutaneous microbiome during wound healing. Future Directions: Further characterization of the mechanisms by which stress-induced molecules influence microbial proliferation and metabolism in wounds is necessary to identify altered microbial phenotypes that differentially influence host innate immune responses required for optimal healing. These mechanisms may yield beneficial as targets for manipulation of the microbiome to further benefit the host after cutaneous injury.

Mechanisms of disease: role of neurotrophins in diabetes and diabetic neuropathy

Neuropathy is an insidious and devastating consequence of diabetes. Early studies provided a strong rationale for deficient neurotrophin support in the pathogenesis of diabetic neuropathy in a number of critical tissues and organs. It has now been over a decade since the first failed human neurotrophin supplementation clinical trials, but mounting evidence still implicates these trophic factors in diabetic neuropathy. Since then, tremendous advances have been made in our understanding of the complexities of neurotrophin signaling and processing and how the diabetic milieu might impact this. This in turn changes both our perception of how the altered trophic environment contributes to the etiology of diabetic neuropathy and the design of future neurotrophin therapeutic interventions. This chapter summarizes some of these findings and attempts to integrate neurotrophin actions on the nervous system with an increasing appreciation of their role in the regulation of metabolic processes in diabetes that impact the diabetic neuropathic state.

Effects of a skin neuropeptide (substance p) on cutaneous microflora

Background

Skin is the largest human neuroendocrine organ and hosts the second most numerous microbial population but the interaction of skin neuropeptides with the microflora has never been investigated. We studied the effect of Substance P (SP), a peptide released by nerve endings in the skin on bacterial virulence.

Methodology/Principal Findings

Bacillus cereus, a member of the skin transient microflora, was used as a model. Exposure to SP strongly stimulated the cytotoxicity of B. cereus (+553±3% with SP 10⁻⁶ M) and this effect was rapid (<5 min). Infection of keratinocytes with SP treated B. cereus led to a rise in caspase1 and morphological alterations of the actin cytoskeleton. Secretome analysis revealed that SP stimulated the release of collagenase and superoxide dismutase. Moreover, we also noted a shift in the surface polarity of the bacteria linked to a peel-off of the S-layer and the release of S-layer proteins. Meanwhile, the biofilm formation activity of B. cereus was increased. The Thermo unstable ribosomal Elongation factor (Ef-Tu) was identified as the SP binding site in B. cereus. Other Gram positive skin bacteria, namely Staphylococcus aureus and Staphylococcus epidermidis also reacted to SP by an increase of virulence. Thermal water from Uriage-les-Bains and an artificial polysaccharide (Teflose®) were capable to antagonize the effect of SP on bacterial virulence.

Conclusions/Significance

SP is released in sweat during stress and is known to be involved in the pathogenesis of numerous skin diseases through neurogenic inflammation. Our study suggests that a direct effect of SP on the skin microbiote should be another mechanism.

Loss of innervation and axon plasticity accompanies impaired diabetic wound healing

Loss of cutaneous innervation from sensory neuropathy is included among mechanisms for impaired healing of diabetic skin wounds. The relationships between cutaneous axons and their local microenvironment during wound healing are challenged in diabetes. Here, we show that secondary wound closure of the hairy dorsal skin of mice is delayed by diabetes and is associated with not only a pre-existing loss of cutaneous axons but substantial retraction of axons around the wound. At 7d following a 3mm punch wound, a critical period of healing and reinnervation, both intact skin nearby the wound and skin directly at the wound margins had over 30-50% fewer axons and a larger deficit of ingrowing axons in diabetics. These findings contrasted with a pre-existing 10-15% deficit in axons. Moreover, new diabetic ingrowing axons had less evidence of plasticity. Unexpectedly, hair follicles adjacent to the wounds had a 70% reduction in their innervation associated with depleted expression of hair follicular stem cell markers. These impairments were associated with the local upregulation of two established axon regenerative ‘roadblocks’: PTEN and RHOA, potential but thus far unexplored mediators of these changes. The overall findings identify striking and unexpected superimposed cutaneous axon loss or retraction beyond that expected of diabetic neuropathy alone, associated with experimental diabetic skin wounding, a finding that prompts new considerations in diabetic wounds.

OnabotulinumtoxinA improves tactile and mechanical pain perception in painful diabetic polyneuropathy

OBJECTIVES

Diabetic neuropathic pain may be relieved by onabotulinumtoxinA (BoNT/A). However, whether BoNT/A changes sensory perception in neuropathic patients remains unknown. This study used a double-blind crossover design to explore the possible effect of BoNT/A on sensory perception.

METHODS

Eighteen patients with painful diabetic polyneuropathy underwent 2 consecutive 12-week periods of treatment either in the sequence of saline (control) and then BoNT/A (SB cohort, n=9) or BoNT/A followed by saline (BS cohort, n=9). Sensory perception was assessed according to the tactile threshold [TT, logarithmized force (g) of von Frey filaments] and mechanical pain threshold [PT, logarithmized weight (g) of weighted syringes], both being averages from 4 individual measurements of bilateral medial and lateral feet obtained at baseline (before injections) and at weeks 1, 4, 8, and 12 after treatment.

RESULTS

In either the SB or the BS cohort, there was a decrease in the TT and the PT after treatment with BoNT/A but not with saline. In the analysis merging both cohorts (n=18), BoNT/A resulted in a significant decrease in TT and PT at weeks 1, 4, 8, and 12 (all Ps<0.05 vs. saline). The longitudinal effect of BoNT/A on TT and PT remained significant when baseline values, treatment sequences, and periods were controlled using generalized estimating equations.

DISCUSSION

BoNT/A may improve tactile and mechanical pain perception in painful diabetic polyneuropathy. The beneficial effects of BoNT/A deserves further study to elucidate the exact mechanism and potential for preventing insensate injuries.

Paracrine loop of keratinocyte proliferation and directed neuritic outgrowth in a neuroepithelial coculture

In the absence of skin innervation, wound healing is delayed and chronic nonhealing wounds may occur. Keratinocytes produce neurotrophic factors, such as nerve growth factor (NGF), which has been suggested to attract primary cutaneous afferent axons and exert mitogenic effects on keratinocytes. The present study was performed to examine the interaction of primary human keratinocytes (hKTs) and rat cutaneous primary afferent dorsal root ganglion (DRG) neurons with regard to neuritic outgrowth and keratinocyte proliferation. Neuritic outgrowth was assessed with neurofilament immunostaining where cell bodies and fine neuritic processes were identified. Neuritic outgrowth of neurons alone in culture is spatially random and radial. Neurites in cocultures of DRG neurons insinuated between the hKTs and grew to "clumps" of hKTs within the cultures. Immunostaining with anti-NGF antibody indicates that hKTs expressed the neurotrophin NGF. Proliferation of keratinocytes was significantly enhanced in coculture with DRG and hKT, and NGF levels were increased as compared to DRG or hKT culture alone. These results indicate a dynamic interaction between DRG neurons and hKTs whereby the DRG neurons issue neurites in association with hKTs and the hKTs up-regulate NGF and increase their proliferation rate. These findings support the hypothesis that nerve-skin interactions play a significant role in wound healing.

Nerve growth factor: from the early discoveries to the potential clinical use

The physiological role of the neurotrophin nerve growth factor (NGF) has been characterized, since its discovery in the 1950s, first in the sensory and autonomic nervous system, then in central nervous, endocrine and immune systems. NGF plays its trophic role both during development and in adulthood, ensuring the maintenance of phenotypic and functional characteristic of several populations of neurons as well as immune cells. From a translational standpoint, the action of NGF on cholinergic neurons of the basal forebrain and on sensory neurons in dorsal root ganglia first gained researcher's attention, in view of possible clinical use in Alzheimer's disease patients and in peripheral neuropathies respectively. The translational and clinical research on NGF have, since then, enlarged the spectrum of diseases that could benefit from NGF treatment, at the same time highlighting possible limitations in the use of the neurotrophin as a drug. In this review we give a comprehensive account for almost all of the clinical trials attempted until now by using NGF. A perspective on future development for translational research on NGF is also discussed, in view of recent proposals for innovative delivery strategies and/or for additional pathologies to be treated, such as ocular and skin diseases, gliomas, traumatic brain injuries, vascular and immune diseases.

[Small fibre neuropathy in primary Sjögren syndrome]

PURPOSE

About forty percent of the patients with primary Sjögren's syndrome (pSS) experience chronic neuropathic pain with normal electrodiagnostic studies. Two previous studies suggest that chronic neuropathic pain in pSS is due to small fiber neuropathy (SFN). Quantification of epidermal nerve fiber density after skin biopsy has been validated to diagnose small fiber neuropathy.

METHODS

Skin biopsy was performed in 14 consecutive pSS patients (satisfying the american-european classification criteria) with chronic neuropathic pain and normal electrodiagnostic studies suggesting SFN.

RESULTS

Fourteen female pSS patients exhibited chronic neuropathic pain [burning sensation (n=14), prickling (n=4), dysesthesia (n=8)] with paroxystic exacerbations (n=10) and allodynia (n=13), for a mean period of 18.4±12.4 months. Neuropathic pain involved mostly hands and feet (n=13), with a distal (n=9) and leg (n=4) predominant distribution. Neurological examination disclosed normal deep tendon responses and absence of motor weakness (n=14). Small fiber neuropathy was confirmed by skin biopsy in 13 cases. Epidermal nerve fiber density was decreased in distal [(n=12), mean 3.5±1.7 fibers/mm (N>6.9)] and proximal site of biopsy [(n=9), mean 7.04±2.63 fibers/mm (N>9.3)].

CONCLUSION

Small fiber neuropathy is commonly responsible of chronic neuropathic pain in pSS. Prevalence, physiopathology and neurological evolution of such neuropathies still remain unknown.

Factors affecting wound healing

Wound healing, as a normal biological process in the human body, is achieved through four precisely and highly programmed phases: hemostasis, inflammation, proliferation, and remodeling. For a wound to heal successfully, all four phases must occur in the proper sequence and time frame. Many factors can interfere with one or more phases of this process, thus causing improper or impaired wound healing. This article reviews the recent literature on the most significant factors that affect cutaneous wound healing and the potential cellular and/or molecular mechanisms involved. The factors discussed include oxygenation, infection, age and sex hormones, stress, diabetes, obesity, medications, alcoholism, smoking, and nutrition. A better understanding of the influence of these factors on repair may lead to therapeutics that improve wound healing and resolve impaired wounds.

Gene expression of pro-inflammatory cytokines and neuropeptides in diabetic wound healing

The interaction between neuropeptides and cytokines and its role in cutaneous wound healing is becoming evident. The goal of the present study is to investigate the impact of diabetes on peripheral cytokine and neuropeptide expression and its role in diabetic wound healing. To achieve this goal, the effect of diabetes on wound healing, along with the role of inflammatory cytokines such as interleukin-6 (IL-6) and interleukin-8 (IL-8) secreted in the wound microenvironment, and neuropeptides such as substance P (SP) and neuropeptide Y (NPY), secreted from peripheral nerves is monitored in non-diabetic and diabetic rabbits. Rabbits in the diabetic group received alloxan monohydrate (100mg/kg i.v.). Ten days after diabetic induction, four full thickness circular wounds were created in both ears using a 6mm punch biopsy. Wound healing was monitored over 10 d and gene expression of cytokines and neuropeptides was assessed in the wounds. Compared with the non-diabetic rabbits, wounds of diabetic rabbits heal significantly slower. Diabetic rabbits show significantly increased baseline gene expression of IL-6 and IL-8, their receptors, CXCR1, CXCR2, GP-130, and a decrease of prepro tachykinin-A (PP-TA), the precursor of SP, whereas the expression of prepro-NPY (PP-NPY), the precursor of NPY is not different. Similarly, baseline protein expression of CXCR1 is higher in diabetic rabbit skin. Post-injury, the increase over baseline gene expression of IL-6, IL-8, CXCR1, CXCR2, and GP-130 is significantly less in diabetic wounds compared with non-diabetic wounds. Although there is no difference in PP-TA gene expression between non-diabetic and diabetic rabbits post-injury, the gene expression of PP-NPY is reduced in diabetic rabbits. In conclusion, diabetes causes dysregulation in the neuropeptide expression in the skin along with a suppressed focused inflammatory response to injury. This suggests that the chronic inflammation in the skin of diabetic rabbits inhibits the acute inflammation much needed for wound healing.

Altered molecular mechanisms of diabetic foot ulcers

The continuously increasing worldwide prevalence of diabetes will be accompanied by a greater incidence of diabetic foot ulcer, a complication in which many of the morphological processes involved in normal wound healing are disrupted. The highly complex and integrated process of wound healing is regulated by a large array of molecular factors. These often have overlapping functions, ensuring a certain degree of tolerance through redundancy. In diabetes, changes to the expression of a large number of molecular factors have been observed, overwhelming this inbuilt redundancy. This results in delayed healing or incomplete healing as in ulceration. Understanding the relationship between altered levels of molecular factors and the inhibited healing process in such ulcers will permit the development of targeted treatments aimed to greatly improve the quality of life of patients, at the same time helping to reduce the huge costs associated with treating this diabetic condition and its long-term consequences. This short review examines how changes in the expression of molecular factors are related to altered morphology in diabetic foot ulceration and very briefly considers treatment strategies at molecular level.

Epidemiology and prevalence of methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis in patients with diabetic foot ulcers: focus on the differences between species isolated from individuals with ischemic vs. neuropathic foot ulcers

We examined whether foot ischemia or neuropathy with diabetic foot ulcer (DFU) promote selection of staphylococci species, evaluated frequency of MRSA and MRSE among strains yielded from patients with DFU and assessed multidrug resistance of isolates. Patients with DFU and foot osteomyelitis were divided into ischemic foot ulcer (IFU, n=21) and neuropathic foot ulcer (NFU, n=29) groups. Frequency of Staphylococcus epidermidis yielded from curettage of IFU was higher compared with NFU (P<0.05). S. epidermidis was also more frequently isolated from the toe web surface of patients with IFU compared with NFU (55% vs. 17.9%, respectively) and healthy volunteers (HV, n=20) (17.6%, P<0.05). These mostly MRSE strains (83.3-100%) originating from DFU patients were multidrug resistant (88.8%). Also, most of MRSA isolates were multidrug resistant (70.3%). Higher rates of MSSA from DFU patients than HV showed resistance to antimicrobials. This is the first report indicating that diabetic patients with IFU differ with NFU patients in higher frequency of S. epidermidis skin colonization and ulcer infection. We suggest that IFU should be defined as separate disease state of DFU and S. epidermidis should be appreciated as a nosocomial pathogen.

Inflammation and neuropeptides: the connection in diabetic wound healing

Abnormal wound healing is a major complication of both type 1 and type 2 diabetes, with nonhealing foot ulcerations leading in the worst cases to lower-limb amputation. Wound healing requires the integration of complex cellular and molecular events in successive phases of inflammation, cell proliferation, cell migration, angiogenesis and re-epithelialisation. A link between wound healing and the nervous system is clinically apparent as peripheral neuropathy is reported in 30-50% of diabetic patients and is the most common and sensitive predictor of foot ulceration. Indeed, a bidirectional connection between the nervous and the immune systems and its role in wound repair has emerged as one of the focal features of the wound-healing dogma. This review provides a broad overview of the mediators of this connection, which include neuropeptides and cytokines released from nerve fibres, immune cells and cutaneous cells. In-depth understanding of the signalling pathways in the neuroimmune axis in diabetic wound healing is vital to the development of successful wound-healing therapies.

The biology of chronic foot ulcers in persons with diabetes

Diabetic foot ulcers constitute a major health problem and they are recalcitrant to healing due to a constellation of intrinsic and extrinsic factors. The purpose of this article is to review the potential biological mechanisms that deter healing and perpetuate inflammatory responses in chronic diabetes foot ulcers. The link between hyperglycemia induced oxidative stress and its negative impact on cellular functions are explained. Key evidence related to alteration in tissue perfusion, bacterial balance, sustained proteases and cytokines release, leukocyte function, and growth factor production at the local wound level are summarized.