Yiwen Niu

Diabetes-impaired wound healing and altered macrophage activation: a possible pathophysiologic correlation.

Macrophages play a critical role in wound healing and can be activated to two distinctive phenotypes in vitro: classical macrophage activation (caM) and alternative macrophage activation (aaM). This study investigated whether the impaired cutaneous repair observed in streptozotocin‐induced diabetic rats was associated with altered macrophage activation. Our results show that macrophage activation phenotypes could be observed in wound healing through double immunostaining. The caM macrophages appeared in the initial stage of wound healing, followed by aaM macrophages, which predominated in normal wounds. However, through examining markers associated with activation by immunoblotting and real‐time polymerase chain reaction (PCR), diabetic wounds demonstrated insufficient caM in the early stage but excessive aaM in the later proliferative phase. Moreover, the macrophage activation markers were correlated with the instructive T helper cell type 1 (Th1)/Th2 cytokines in both groups. It was indicated that changed macrophage activation might contribute to impaired healing in diabetes wounds, and that strategies for reverting this abnormal activation could be useful for enhancing the wound healing process.

Effects of extracellular matrix glycosylation on proliferation and apoptosis of human dermal fibroblasts via the receptor for advanced glycosylated end products.

The balance between proliferation and apoptosis of skin cells is responsible for skin turnover and the success of the wound healing process. Recent reports have shown that advanced glycosylation end product (AGE) formation participates in dermatologic problems in diabetes. However, the effect on proliferation and apoptosis of dermal fibroblasts remains unclear. The aim of this study was to investigate the effects of dermal microenvironment glycosylation on the balance of cellular proliferation and apoptosis. Histology and immunohistochemical staining were performed on type II diabetic and nondiabetic skin tissue specimens to determine the distributions of proliferating cell nuclear antigen, apoptotic cells, AGEs, and receptors for AGEs (RAGEs). Matrix secreted by cultured human fibroblasts was glycosylated by 0.5 M D-ribose. RAGE-blocking antibodies were applied to inhibit the interaction of RAGE and AGEs in this system and then cell viability, cell cycle phase distribution, and apoptosis were measured. Diabetic skin has degenerative, loosely arranged collagen and increased apoptotic cells compared with normal skin. Expression of AGE and RAGE in diabetic skin tissue increased. Glycosylated matrix induced cell cycle arrest and apoptosis of cultured dermal fibroblasts, whereas application of RAGE-blocking antibodies redressed these changes. The accumulation of glycosylated extracellular matrix in diabetic skin tissue is a critical mediator of cellular function. Mediation of RAGE affects the balance of cellular proliferation and apoptosis, which confirms that diabetic wounds possess atypical origin in the repair process.

Reduced Dermis Thickness and AGE Accumulation in Diabetic Abdominal Skin

Dermatological problems in diabetes might play an important role in the spontaneous ulcers and impaired wound healing that are seen in diabetic patients. Investigation of the cause of diabetic skin disorders is critical for identifying effective treatment. The abdominal full-thickness skin tissues of 33 patients (14 nondiabetic and 19 diabetic) were analyzed. The cell viability and malondialdehyde (MDA) production of fibroblasts were measured after advanced glycosylation end product (AGE)–bovine serum albumin (BSA) exposure. Cutaneous histological observation showed reduced thickness of the diabetic abdominal dermis with morphological characteristics of obscured multilayer epithelium and shortened, thinned, and disorganized collagen fibrils with focal chronic inflammatory cell infiltration when compared with controls of the same age. Accumulation of AGEs in diabetic skin was prominent. Less hydroxyproline, higher myeloperoxidase activity, and increased MDA content were detected in diabetic skin. In vitro, the time- and dose-dependent inhibitory effects of AGE-BSA on fibroblast viability as well as the fact that AGE-BSA could promote MDA production of fibroblasts were shown. It is shown that the accumulation of AGEs in diabetic skin tissue induces an oxidative damage of fibroblasts and acts as an important contributor to the thinner diabetic abdominal dermis. The authors believe that diabetic cutaneous properties at baseline may increase the susceptibility to injury, and diabetic wounds possess atypical origin in the repair process.

The Relationship Between Inflammation and Impaired Wound Healing in a Diabetic Rat Burn Model.

Inflammation, initiated by polymorphonuclear neutrophil (PMNs) infiltration, is the first step in wound healing. The aim of this study is to investigate the function of neutrophils in a diabetes-impaired wound healing model and to explore the underlying mechanisms leading to neutrophil dysfunction. Superficial second-degree burns were created in the streptozotocin (STZ)-induced diabetic rat model, and the changes in the levels of advanced glycation end products (AGE), receptor of AGE (RAGE), inflammatory cytokines and oxidative markers, as well as cell apoptosis were determined. The effects of AGE on isolated PMNs were also determined in vitro. We found that deposition of AGE in diabetic rat skin activated the neutrophils before injury. However, the dense inflammatory band failed to form in the diabetic rats after injury. Compared with the controls, enhanced expression of RAGE and accelerated cell apoptosis were observed in the burned skin of diabetic rats. The altered expression pattern of inflammatory cytokines (tumor necrosis factor-alpha and interleukin-8) and oxidative markers (glutathione peroxidase, myeloperoxidase, hydrogen peroxide, and malondialdehyde) between burned skin of diabetic and control rats revealed delayed neutrophil chemotaxis and respiratory burst. Furthermore, the results in vitro showed that exposure to AGE inhibited the viability of PMNs, promoted RAGE production and cell apoptosis, and prevented the migration of PMNs, consistent with the findings in vivo. Besides, AGE-treated neutrophils showed increased secretion of inflammatory cytokines and increased oxidative stress. Combined, our results suggest that an interaction between AGE and its receptors inhibits neutrophil viability and function in the diabetic rat burn model.

Hydrogen Peroxide: A Potential Wound Therapeutic Target

Hydrogen peroxide (H₂O₂) is a topical antiseptic used in wound cleaning which kills pathogens through oxidation burst and local oxygen production. H₂O₂ has been reported to be a reactive biochemical molecule synthesized by various cells that influences biological behavior through multiple mechanisms: alterations of membrane potential, generation of new molecules, and changing intracellular redox balance, which results in activation or inactivation of different signaling transduction pathways. Contrary to the traditional viewpoint that H₂O₂ probably impairs tissue through its high oxidative property, a proper level of H₂O₂ is considered an important requirement for normal wound healing. Although the present clinical use of H₂O₂ is still limited to the elimination of microbial contamination and sometimes hemostasis, better understanding towards the sterilization ability and cell behavior regulatory function of H₂O₂ within wounds will enhance the potential to exogenously augment and manipulate healing.

A Severely Infected Diabetic Foot Treated Successfully Without Using Systemic Antibiotics

About 50% to 70% of all lower extremity amputations are related to diabetes infection. And antibiotic therapy is routinely used for all infected wounds to reduce the mortality of diabetic foot. Here, we report a case of diabetic foot with acute and deep severe infection. During hospital therapy, we used negative pressure therapy and extensive debridement without systemic antibiotic application, and we successfully rescued a foot from amputation. Negative pressure therapy and extensive debridement are very important and effective methods to control infection and promote wound healing in diabetes foot.

Aminoguanidine cream ameliorates skin tissue microenvironment in diabetic rats

Introduction The aim of the study was to explore the effect of aminoguanidine cream on the skin tissue microenvironment in diabetic rats. Material and methods A total of 51 healthy male Sprague Dawley (SD) rats were randomly divided into three groups: the diabetes group (n = 18), the aminoguanidine group (n = 18) and the control group (n = 15). Rats in the diabetes group and aminoguanidine group were injected with 65 mg/kg streptozotocin to induce the diabetes model, and in the control group with citrate buffer. After successful induction of diabetes, the back hair of all rats was stripped by barium sulfide, and the aminoguanidine group was treated with aminoguanidine cream using disinfected cotton swabs twice every day for 40 days, while the diabetes and control groups were treated with the cream matrix. The pathological changes of skin were observed by HE staining, while the content of inflammatory cytokines (TNF-α, IL-8, ICAM and IL-1α) and the antioxidant indexes (T-AOC, GSH-PX, MPO MDA H2O2) were examined using commercial kits. Results After 40 days of treatment, the diabetes group manifested tissue lesions, whereas the aminoguanidine group seemed normal. Compared with the diabetes group, the content of inflammatory cytokines TNF-α, IL-8, ICAM and IL-1α was dramatically lower in the aminoguanidine group. T-AOC in all groups underwent dramatic changes and returned to normal finally. The activities of GSH-PX and MPO and content of H2O2 in the diabetes group were all higher than those in the aminoguanidine group. Conclusions Aminoguanidine may have a good systemic effect on alleviating the pathological changes of skin tissue in diabetic rats, which may be attributed to the regulation of GSH-PX, TNF-α, IL-8, ICAM and IL-1α.

Blocking AGE-RAGE Signaling Improved Functional Disorders of Macrophages in Diabetic Wound

Advanced glycosylation end products (AGEs) accumulate in diabetic wounds. Interactions between AGEs and their receptor (RAGE) leads to dermatologic problems in diabetes. Macrophage, which plays important roles in wound healing, highly expresses RAGE. Therefore, we investigated whether RAGE-expressing macrophages might be responsible for impaired wound healing on diabetes. We used anti-RAGE antibody applied topically on diabetic wounds. After confirming that wound healing was improved in anti-RAGE antibody group compared with normal mice, our results showed that macrophages appeared insufficient in the early stage and fading away slowly in the later proliferative phase compared with the control group, which was ameliorated in anti-RAGE antibody-applied wounds. Blocking AGE-RAGE signaling also increased neutrophils phagocytized by macrophages and promoted the phenotypic switch of macrophages from proinflammatory to prohealing activities. In vitro, phagocytosis of THP-1 (M0) and lipopolysaccharide- (LPS-) induced (M1) macrophages was impaired by treatment with AGEs, while IL-4- and IL-13-induced (M2) macrophages was not. Finally, AGEs increased the proinflammatory response of M1 macrophages, while inhibiting the polarization and anti-inflammatory functions of M2 macrophages. In conclusion, inhibition of AGE-RAGE signaling improved functional disorders of macrophages in the early inflammatory phase, which promoted the healing of wounds in diabetic mice.

A Potential Mechanism for Diabetic Wound Healing: Cutaneous Environmental Disorders

Diabetes mellitus is a chronic multi-organ metabolic disorder caused by a combination of environmental and genetic factors. Diabetic complications are considered to be multifactorial with increasing evidence that one of the major pathways involved in the progression of both microvascular and macrovascular diseases is the biochemical process of advanced glycation. We will combine in vitro and in vivo studies and other related literatures to discuss the role of advanced glycation end products (AGEs), which may exert deleterious effects in diabetes. Dr Shuliang Lu puts forward the theory of ‘cutaneous environmental disorders’ mediated by AGEs. The receptor for advanced glycation end products (RAGE) was first described as a signal transduction receptor for AGEs. Recent discoveries regarding AGEs-RAGE interactions expanded our understanding of the mechanisms by which RAGE evoked pathological consequences. In this chapter, we report on the biology of AGEs, AGEs and wound healing, as well as address current strategies to interrupt the formation of AGEs and underscore strategies by which antagonism of RAGE and AGEs-RAGE crosslinks may be realized.

Effects of advanced glycation end-products (AGEs) on skin keratinocytes by nuclear factor-kappa B (NF-κB) activation

Advance glycation end-products (AGEs) are produced in patients with long-term hyperglycemia metabolic disorder and responsible for multiple symptoms including impaired wound healing. This study was designed to reveal the roles and possible mechanism of AGE in diabetic wound healing. Sixteen Sprague-Dawley (SD) rats were divided into two groups randomly; the streptozotocin (STZ) induced diabetic group and the normal group. Eight weeks later, epidermal growth factor (EGF) and AGE levels, nuclear factor-kappa B (NF-κB) localization and cell viability were measured in vivo. Keratinocytes from normal skin were cultured in AGE-enriched conditional media, and the cell viability, apoptosis, adhesion and migration were detected in order to find the directed evidence between AGE and keratinocytes. AGE content was higher and NF-κB expression was more localized in the nuclear of keratinocytes in diabetic skins. AGE could inhibit normal cell growth by inducing apoptosis and arresting cell division cycle, inhibiting cell adhesion and promoting migration which might be mediated by NF-κB in vitro. Blocking NF-κB activity could reverse effects of AGE on cell proliferation and migration, but not adhesion. Therefore, AGE could damage the skin keratinocytes function in vivo and in vitro, and the activation of NF-κB is involved in this process. Key words : AGE, NF-kappaB, keratinocytes, diabetes, wound healing.