Pathogenesis and Treatment of Impaired Wound Healing in Diabetes Mellitus: New Insights

Diabetic foot ulcers (DFUs) are one of the most common and serious complications of diabetes mellitus, as wound healing is impaired in the diabetic foot. Wound healing is a dynamic and complex biological process that can be divided into four partly overlapping phases: hemostasis, inflammation, proliferative and remodeling. These phases involve a large number of cell types, extracellular components, growth factors and cytokines. Diabetes mellitus causes impaired wound healing by affecting one or more biological mechanisms of these processes. Most often, it is triggered by hyperglycemia, chronic inflammation, micro- and macro-circulatory dysfunction, hypoxia, autonomic and sensory neuropathy, and impaired neuropeptide signaling. Research focused on thoroughly understanding these mechanisms would allow for specifically targeted treatment of diabetic foot ulcers. The main principles for DFU treatment are wound debridement, pressure off-loading, revascularization and infection management. New treatment options such as bioengineered skin substitutes, extracellular matrix proteins, growth factors, and negative pressure wound therapy, have emerged as adjunctive therapies for ulcers. Future treatment strategies include stem cell-based therapies, delivery of gene encoding growth factors, application of angiotensin receptors analogs and neuropeptides like substance P, as well as inhibition of inflammatory cytokines. This review provides an outlook of the pathophysiology in diabetic wound healing and summarizes the established and adjunctive treatment strategies, as well as the future therapeutic options for the treatment of DFUs.     

Effects of Non-thermal,Non-cavitational Ultrasound Exposure on Human Diabetic Ulcer Healing and Inflammatory Gene Expression in a Pilot Study

The purpose of this clinical study was to assess, in a limited patient population, the potential for a novel advanced wound care treatment based on low-frequency (20 kHz) low-intensity (spatial peak temporal peak intensity <100 mW/cm²; i.e., pressure amplitude of 55 kPa) ultrasound (LFLI-US), to affect wound closure rate in human diabetic foot ulcers (DFUs) and to effect changes in the relative expression of pro-inflammatory and anti-inflammatory genes. The ratio of expression of these genes, termed the M1/M2 score because it was inspired by the transition of macrophages from pro-inflammatory (M1) to anti-inflammatory (M2) phenotypes as wound healing progresses, was previously presented as a potential healing indicator for DFUs treated with the standard of care. We previously found that non-cavitational, non-thermal LFLI-US delivered with a pulse repetition frequency of 25 Hz was effective at improving wound healing in a pilot study of 20 patients with chronic venous ulcers. In this study, we assessed the potential for weekly LFLI-US exposures to affect wound healing in patients with diabetic ulcers, and we analyzed temporal changes in the M1/M2 score in debrided diabetic wound tissue. Although this was a limited patient population of only 8 patients, wounds treated with LFLI-US exhibited a significantly faster reduction in wound size compared with sham-treated patients (p < 0.001). In addition, the value of the M1/M2 score decreased for all healing diabetic ulcers and increased for all non-healing diabetic ulcers, suggesting that the M1/M2 score could be useful as an indicator of treatment efficacy for advanced DFU treatments. Such an indicator would facilitate clinical decision making, ensuring optimal wound management and thus contributing to reduction of health care expenses. Moreover, the results presented may contribute to an understanding of the mechanisms underlying ultrasonically assisted chronic wound healing. Knowledge of these mechanisms could lead to personalized or patient-tailored treatment.     

Pneumatic compression in the treatment of chronic ulcers

Abstract

Objective: To review existing literature that examines physiological mechanisms and clinical effects of different types of pneumatic compression (PC) therapy in the treatment of chronic wounds.

Methods: Electronic databases were searched using intermittent, sequential, cardiosynchronous, pneumatic, compression, ulcer, wound, healing, and treatment as key words. All clinical studies were included provided the study subjects had chronic wounds, the treatment included PC, and wound healing was a measured outcome. Original clinical reports investigating the physiological effects of PC were also retrieved and reviewed.

Results: There is a strong physiological basis behind the use of PC for improving venous and arterial circulation. Six randomised controlled trials (RCTs) have compared the effect of PC to compression therapy or standard wound care on the healing of venous ulcers. However, these RCTs have produced conflicting results. One recent controlled clinical trial reported significantly improved healing and reduced amputation rate of people with chronic arterial ulcers. A well designed RCT also demonstrated greater oedema reduction and faster healing of diabetic foot ulcers compared to sham controls. Research is emerging to delineate optimal treatment protocols.

Conclusion: PC may be a valuable adjunct to aid in the treatment of individuals with venous, arterial, and diabetic ulcers. It should be considered for those people who are not compliant with compression bandaging or those at risk of limb amputation.     

Cellular and molecular basis of wound healing in diabetes

Diabetic foot ulcers (DFUs), a leading cause of amputations, affect 15% of people with diabetes. A series of multiple mechanisms, including decreased cell and growth factor response, lead to diminished peripheral blood flow and decreased local angiogenesis, all of which can contribute to lack of healing in persons with DFUs. In this issue of the JCI, Gallagher and colleagues demonstrate that in diabetic mice, hyperoxia enhances the mobilization of circulating endothelial progenitor cells (EPCs) from the bone marrow to the peripheral circulation (see the related article beginning on page 1249). Local injection of the chemokine stromal cell-derived factor-1alpha then recruits these EPCs to the cutaneous wound site, resulting in accelerated wound healing. Thus, Gallagher et al. have identified novel potential targets for therapeutic intervention in diabetic wound healing.     

Intracellular Staphylococcus aureus triggers pyroptosis and contributes to inhibition of healing due to perforin-2 suppression

Impaired wound healing associated with recurrent Staphylococcus aureus infection and unresolved inflammation are hallmarks of nonhealing diabetic foot ulcers (DFUs). Perforin-2, an innate immunity molecule against intracellular bacteria, limits cutaneous infection and dissemination of S. aureus in mice. Here, we report the intracellular accumulation of S. aureus in the epidermis of DFUs with no clinical signs of infection due to marked suppression of perforin-2. S. aureus residing within the epidermis of DFUs triggers AIM2 inflammasome activation and pyroptosis. These findings were corroborated in mice lacking perforin-2. The effects of pyroptosis on DFU clinical outcomes were further elucidated in a 4-week longitudinal clinical study in patients with DFUs receiving standard care. Increased AIM2 inflammasome and ASC-pyroptosome coupled with induction of IL-1β were found in nonhealing DFUs compared with healing DFUs. Our findings revealed that perforin-2 suppression, intracellular S. aureus accumulation, and associated induction of pyroptosis contribute to healing inhibition and prolonged inflammation in patients with DFUs.     

Suppressed recruitment of alternatively activated macrophages reduces TGF-β1 and impairs wound healing in streptozotocin-induced diabetic mice

BackgroundDiabetes mellitus inhibits wound-induced angiogenesis, impairing the wound healing process and leading to the development of chronic wounds. Impaired healing of diabetic wounds is caused by persistent pro-inflammatory macrophages recruited to the granulation tissue; however, little is known about the phenotype of the macrophages involved in diabetic wound healing. The present study was conducted to examine the involvement of macrophages in impaired wound healing using streptozotocin (STZ)-induced diabetic mice.MethodsFull-thickness skin wounds were created on the backs of mice treated with STZ or vehicle.ResultsCompared with controls, wound healing and angiogenesis were suppressed in STZ-treated mice, with attenuated expression of vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF)-2 in wound granulation tissue. STZ-treated mice exhibited enhanced recruitment of classically activated macrophages (M1) expressing inducible nitric oxide synthase (iNOS) and suppressed recruitment of alternatively activated macrophages (M2) expressing transforming growth factor-beta-1 (TGF-β1). Treatment of diabetic mice with TGF-β1 restored wound healing and angiogenesis and normalized M1/M2 macrophage polarization in the granulation tissue.ConclusionsThese results suggest that an imbalance of macrophage phenotypes contributes to impaired wound healing in STZ-induced diabetic mice, and treatment with cytokines derived from M2 macrophages may be an effective therapeutic strategy to increase angiogenesis and promote healing of diabetic wounds.     

Biological therapies for the treatment of cutaneous wounds: Phase III and launched therapies

Introduction: Normal wound healing mechanisms can be overwhelmed in the setting of complex acute and chronic tissue injury. Biological therapies are designed to augment and/or restore the body's natural wound healing abilities. There are a variety of available and emerging technologies utilizing this approach that have demonstrated the ability to augment wound healing.

Areas covered: In this review, the clinical data on launched and emerging biological therapies for wound healing applications are summarized. The methodologies discussed include biological skin equivalents, growth factors/small molecules and stem cell-based therapies.

Expert opinion: While many products possess convincing clinical data demonstrating their efficacy in comparison to standard treatment options, more robust, controlled studies are needed to determine the relative value among established and emerging biological therapies. Future bioengineering and stem cell-based approaches are of particular interest due to the simultaneous correction of multiple deficiencies present in the nonhealing wound.     

Potential benefits of allogeneic bone marrow mesenchymal stem cells for wound healing

Introduction: It is becoming increasingly evident that select adult stem cells have the capacity to participate in repair and regeneration of damaged and/or diseased tissues. Mesenchymal stem cells have been among the most studied adult stem cells for the treatment of a variety of conditions, including wound healing.

Areas covered: Mesenchymal stem cell features potentially beneficial to cutaneous wound healing applications are reviewed.

Expert opinion: Given their potential for in vitro expansion and immune modulatory effects, both autologous and allogeneic mesenchymal stem cells appear to be well suited as wound healing therapies. Allogeneic mesenchymal stem cells derived from young healthy donors could have particular advantage over autologous sources where age and systemic disease can be significant factors.     

Are hair follicle stem cells promising candidates for wound healing?

Introduction: With the continued focus on in-depth investigations of hair follicle stem cells (HFSCs), the role of HFSCs in wound healing has attracted increasing attention from researchers. This review may afford meaningful implications for HFSC treatment of wounds.

Areas covered: We present the properties of HFSCs, analyze the possibility of HFSCs in wound healing, and sum up the recent studies into wound repair with HFSCs. The details of HFSCs in wound healing have been discussed. The possible mechanisms of wound healing with HFSCs have been elaborated. Additionally, the factors that influence HFSCs in wound healing are also summarized.

Expert opinion: Hair follicle stem cells are promising sources for wound healing. However, a further understanding of human HFSCs and the safety use of HFSCs in clinical practice still remain in relative infancy.     

Diabetic Foot Ulcers and Cardiac Autonomic Neuropathy

PurposeDiabetic foot ulcers (DFUs) and cardiac autonomic neuropathy (CAN) are severe complications of diabetes mellitus (DM). Both DFU and CAN are associated with increased risk of major cardiovascular events and mortality. Because of the clinical impact of both these conditions, it is important to establish what effect the presence of CAN has on DFU outcomes.MethodsThis is a narrative review of original research articles identified through an electronic search of PubMed, Scopus, and Google scholar databases until June 2021 exploring CAN in individuals with DFUs. We explored prevalence, patient outcomes (DFU healing and amputation), and mortality.FindingsEvidence suggests that the prevalence of CAN is high, ranging from 43% to 66% among those with DFUs. The presence of CAN may also increase the odds of developing DFUs. A single-center, prospective, observational study has suggested that the presence of CAN significantly reduces DFU healing time. The impact on amputation is indeterminate, with conflicting reports from studies reporting either no or increased risk. On the basis of limited evidence, CAN may be associated with increased mortality in individuals with DFUs.ImplicationsThe interplay between CAN and DFUs is poorly understood from current literature. Given the high prevalence of CAN in individuals with DFUs and the potential for suboptimal outcomes, further high-quality studies are required to determine future management approaches when both conditions coexist and to establish whether early CAN screening in individuals with diabetes at high risk of foot ulceration may ultimately improve their outlook.     

Promising effects of exosomes isolated from menstrual blood‐derived mesenchymal stem cell on wound‐healing process in diabetic mouse model

Wound healing is a complicated process that contains a number of overlapping and consecutive phases, disruption in each of which can cause chronic nonhealing wounds. In the current study, we investigated the effects of exosomes as paracrine factors released from menstrual blood‐derived mesenchymal stem cells (MenSCs) on wound‐healing process in diabetic mice. The exosomes were isolated from MenSCs conditioned media using ultracentrifugation and were characterized by scanning electron microscope and western blotting assay. A full thickness excisional wound was created on the dorsal skin of each streptozotocin‐induced diabetic mouse. The mice were divided into three groups as follows: phosphate buffered saline, exosomes, and MenSC groups. We found that MenSC‐derived exosomes can resolve inflammation via induced M1–M2 macrophage polarization. It was observed that exosomes enhance neoangiogenesis through vascular endothelial growth factor A upregulation. Re‐epithelialization accelerated in the exosome‐treated mice, most likely through NF‐κB p65 subunit upregulation and activation of the NF‐κB signaling pathway. The results demonstrated that exosomes possibly cause less scar formation through decreased Col1:Col3 ratio. These notable results showed that the MenSC‐derived exosomes effectively ameliorated cutaneous nonhealing wounds. We suggest that exosomes can be employed in regenerative medicine for skin repair in difficult‐to‐heal conditions such as diabetic foot ulcer.     

Evaluation of Diabetic Foot Ulcer Healing With Hyperspectral Imaging of Oxyhemoglobin and Deoxyhemoglobin

OBJECTIVE

Foot ulceration remains a major health problem for diabetic patients and has a major impact on the cost of diabetes treatment. We tested a hyperspectral imaging technology that quantifies cutaneous tissue hemoglobin oxygenation and generated anatomically relevant tissue oxygenation maps to assess the healing potential of diabetic foot ulcers (DFUs).

RESEARCH DESIGN AND METHODS

A prospective single-arm blinded study was completed in which 66 patients with type 1 and type 2 diabetes were enrolled and followed over a 24-week period. Clinical, medical, and diabetes histories were collected. Transcutaneous oxygen tension was measured at the ankles. Superficial tissue oxyhemoglobin (oxy) and deoxyhemoglobin (deoxy) were measured with hyperspectral imaging from intact tissue bordering the ulcer. A healing index derived from oxy and deoxy values was used to assess the potential for healing.

RESULTS

Fifty-four patients with 73 ulcers completed the study; at 24 weeks, 54 ulcers healed while 19 ulcers did not heal. When using the healing index to predict healing, the sensitivity was 80% (43 of 54), the specificity was 74% (14 of 19), and the positive predictive value was 90% (43 of 48). The sensitivity, specificity, and positive predictive values increased to 86, 88, and 96%, respectively, when removing three false-positive osteomyelitis cases and four false-negative cases due to measurements on a callus. The results indicate that cutaneous tissue oxygenation correlates with wound healing in diabetic patients.

CONCLUSIONS

Hyperspectral imaging of tissue oxy and deoxy may predict the healing of DFUs with high sensitivity and specificity based on information obtained from a single visit.Diabetes is a major global disease that affects 194 million people worldwide and is expected to increase in prevalence to 344 million by the year 2030 (1). One major complication of diabetes is foot ulceration, which occurs in as many as 15–25% of type 1 and type 2 diabetic patients over their lifetimes (2–4). Studies show that between 2 and 6% of diabetic patients will develop a foot ulcer every year (5,6). The feet of patients with diabetes are at risk for ulceration due to a wide range of pathological conditions, the major three being peripheral neuropathy, foot deformity, and trauma, which may be exacerbated by comorbid peripheral vascular disease (4,7). If left untreated, foot ulcers lead to infection and deep-tissue necrosis (8).Foot pathology is a major source of morbidity in patients with diabetes and is a leading cause of hospitalization. Infected and/or ischemic diabetic foot ulcers (DFUs) account for about 25% of all hospital visits among patients with diabetes. Previous studies have shown that a DFU preceeds roughly 85% of all lower-extremity amputations in patients with diabetes (9,10), and more than 88,000 amputations are performed annually on diabetic patients (11). The cost to manage foot disorders is estimated at several billion dollars annually (5,12). Successful clinical management of DFUs not only has the potential to reduce the cost of caring for these patients but also to improve quality of life by reducing comorbidities.Current treatment options for DFUs include offloading to reduce pressure on the wound, wound care to prevent infections, and wound debridement to remove necrotic debris and restimulate the wound healing process (11,13,14). Even with these measures, some wounds fail to heal. Having a means to assess healing potential may help triage wounds earlier to more aggressive therapies, thereby avoiding infections and amputations.Clinical measurements of microvascular function may be an important part of DFU assessment (15–17). Hyperspectral imaging (HSI) was developed as a novel noninvasive diagnostic tool to quantify tissue oxygenation and generate anatomically relevant maps of microcirculatory changes seen in diabetic patients (18). HSI generates a map of regions of interest based on local molecular composition. With proper wavelength selection, spatial maps of molecules such as oxyhemoglobin (oxy) and deoxyhemoglobin (deoxy) can be acquired.A pilot study of 10 type 1 diabetic patients with 21 DFU sites showed that HSI identified changes in tissue oxygenation in the diabetic foot that were predictive of ulcer healing (18). The sensitivity, specificity, and positive predictive value of the healing index were 93, 86, and 93%, respectively. The goal of the current study was to test the accuracy of HSI in evaluating the healing potential of DFUs in a large number of type 1 and 2 diabetic patients.     

Heme Oxygenase-1 Accelerates Cutaneous Wound Healing in Mice

Heme oxygenase-1 (HO-1), a cytoprotective, pro-angiogenic and anti-inflammatory enzyme, is strongly induced in injured tissues. Our aim was to clarify its role in cutaneous wound healing. In wild type mice, maximal expression of HO-1 in the skin was observed on the 2^nd and 3^rd days after wounding. Inhibition of HO-1 by tin protoporphyrin-IX resulted in retardation of wound closure. Healing was also delayed in HO-1 deficient mice, where lack of HO-1 could lead to complete suppression of reepithelialization and to formation of extensive skin lesions, accompanied by impaired neovascularization. Experiments performed in transgenic mice bearing HO-1 under control of keratin 14 promoter showed that increased level of HO-1 in keratinocytes is enough to improve the neovascularization and hasten the closure of wounds. Importantly, induction of HO-1 in wounded skin was relatively weak and delayed in diabetic (db/db) mice, in which also angiogenesis and wound closure were impaired. In such animals local delivery of HO-1 transgene using adenoviral vectors accelerated the wound healing and increased the vascularization. In summary, induction of HO-1 is necessary for efficient wound closure and neovascularization. Impaired wound healing in diabetic mice may be associated with delayed HO-1 upregulation and can be improved by HO-1 gene transfer.     

Screening for identification of patients at high risk for diabetes-related foot ulcers: a cross-sectional study

ObjectiveDiabetes affected 463 million people globally in 2019, and this number is anticipated to reach 700 million by 2045. Diabetes results in lower limb amputation every 30 seconds. Egypt has a high prevalence of diabetic foot disease among patients with type 2 diabetes mellitus (T2DM). We aimed to identify high-risk patients for diabetic foot ulcers (DFUs) in Egypt.MethodsWe designed a cross-sectional study among adult patients with diabetes at Asyut University Hospital. Inlow’s 60-second diabetic foot screening tool was used to assess the risk of DFU. Neuropathy was assessed using the 10g monofilament test, and laboratory testing was performed to assess glycosylated hemoglobin (HbA1c) and diabetes control levels.ResultsParticipants were aged 46.11 ± 9.18 years; 56% had T2DM and HbA1c levels >7%. In total, 47.9% of participants were at risk for DFUs. This risk was higher in patients who were older, male, widowed, working, illiterate, living in rural areas, and patients with diabetes duration >10 years, body mass index >32 kg/m², uncontrolled blood glucose levels, on an insulin regimen, and smokers.ConclusionsIncreasing health care providers’ awareness and ability to identify high-risk patients is critical to prevent DFUs and reduce the risk of amputation.     

Quality of life in patients with diabetic foot ulcers

PURPOSE: To compare Quality of Life (QoL) between diabetic patients with (former or present) and without foot ulcers. METHODS: Two patient groups of comparable age, sex distribution, type distribution and duration of diabetes were studied. Fourteen patients with former or present, but clinically stable diabetic foot ulcers (DFUs) were studied. The control group was 24 unknown patients with DFUs. None of the participants had other diabetic complications or conditions that would potentially affect QoL. A diabetic foot risk score and QoL were assessed. QoL was scored with the RAND-36, the Barthel Score (ADL) and the Walking and Walking Stairs Questionnaire (WSQ). RESULTS: Marked and significant differences were found in physical functioning (p < 0.001), social functioning (p < 0.05), physical role (p < 0.001) and health experience (p < 0.05) between the two groups with the RAND-36 and the four subscales of the WSQ (all p < 0.001). On all these scales, QoL was significantly poorer in the study group. A correlation was found between the risk scores and QoL (physical functioning and physical role Spearman's r: -0.66, -0.56 and WSQ -0.63, -0.64, -0.67 and 0.71, respectively). CONCLUSION: Presence or history of DFUs has a large impact on physical role, physical functioning and mobility. Physical impairments especially influenced QoL. Probably, QoL can be increased by providing attention that will enhance mobility and by giving advice about adaptations and special equipment.     

Stem cell therapies for wound healing

Introduction: Aberrant wound healing is a significant healthcare problem, posing a substantial burden on patients, their families, and the healthcare system. Existing treatment options remain only moderately effective and often fail to promote the closure of non-healing wounds in susceptible populations, such as aging and diabetic patients. Stem cell therapy has emerged as a promising treatment modality, with the potential to restore tissue to its pre-injured state. Of particular interest are mesenchymal stromal cells, which have been shown to accelerate wound healing by modulating the immune response and promoting angiogenesis.

Areas covered: This review provides an overview of wound healing and current methods for the management of chronic wounds, as well as the current state and considerations for optimizing stem cell therapy. Considerations include stem cell types, tissue source, donor selection, cell heterogeneity, delivery methods, and genetic engineering.

Expert opinion: A growing body of evidence has shown that delivery of stem cells, particularly mesenchymal stromal cells, has the potential to effectively improve the rate and quality of wound healing. However, significant additional basic and clinical research must be performed to optimize cell therapy, such as further elucidation of the therapeutic mechanisms of stem cells and standardization of clinical trial guidelines.     

Clinical and functional correlates of foot pain in diabetic patients

Purpose: Patients with diabetes mellitus frequently suffer from foot pain. This pain seems to be a neglected area in studies on the diabetic foot. The purpose of this study was to identify clinical variables associated with foot pain in diabetic patients. In addition, the relationships between foot pain and several functional impairments and disabilities were explored.

Method: The research group consisted of 29 diabetic patients with any symptoms possibly associated with a diabetic foot, who were referred to podiatry. The relationships between several clinical measures and foot pain were analysed by means of Mann-Whitney U-tests. In addition, Spearman rank correlations coefficients were computed to assess the relationships between foot pain and measures of functional health.

Results: Diabetic patients suffering from sensory neuropathy experience more severe foot pain. Furthermore, patients with more severe foot pain experience more fatigue, more disabilities in walking and a lower level of affective well-being.

Conclusion: Based on these findings this paper concludes that foot pain in diabetic patients is an important impairment, which deserves further scientific attention.     

缺血性糖尿病足部溃疡皮肤Vδ1T细胞胰岛素样生长因子1与诱生型一氧化氮合酶的表达

背景：皮肤Vδ1T细胞分泌的一系列细胞因子能促进伤口愈合,但与糖尿病足部皮肤组织溃疡难以愈合的关系尚未见报道。目的：观察缺血性糖尿病患者足部溃疡皮肤Vδ1T细胞中胰岛素样生长因子1与诱生型一氧化氮合酶的表达。方法：选取缺血性糖尿病足部溃疡患者及正常对照者足部全层皮肤,各10例。双酶标免疫荧光标记测量Vδ1T细胞及胰岛素样生长因子1、诱生型一氧化氮合酶蛋白表达。结果与结论：缺血性糖尿病足部溃疡患者Vδ1T细胞中胰岛素样生长因子1蛋白表达较对照者明显减少（P〈0.01）;诱生型一氧化氮合酶蛋白表达明显增加（P〈0.01）。提示Vδ1T细胞中胰岛素样生长因子1减少可能与缺血性糖尿病足部溃疡难以愈合有关,而胰岛素样生长因子1减少与溃疡皮肤Vδ1T细胞诱生型一氧化氮合酶表达增加,产生氧化应激有关。