Dibutyryl cAMP influences endothelial progenitor cell recruitment during wound neovascularization

Arginine-Nanoenzyme with Timely Angiogenesis for Promoting Diabetic Wound Healing

The successful treatment of diabetic wounds requires strategies that promote anti-inflammation, angiogenesis, and re-epithelialization of the wound. Excessive oxidative stress in diabetic ulcers (DUs) inhibits cell proliferation and hinders timely vascular formation and macrophage polarization from pro-inflammatory M1 to anti-inflammatory M2, resulting in a persistent inflammatory environment and a nonhealing wound. We designed arginine-nanoenzyme (FTA) with mimic-catalase and arginine-loading. 2,3,4-trihydroxy benzaldehyde and arginine (Arg) were connected by a Schiff base bond, and the nanoassembly of Arg to FTA was driven by the coordination force between a ferric ion and polyphenol and noncovalent bond force such as a hydrogen bond. FTA could remove excess reactive oxygen species at the wound site in situ and convert it to oxygen to improve hypoxia. Meanwhile, Arg was released and catalytically metabolized by NO synthase in M1 to promote vascular repair in the early phase. In the late phase, the metabolite of Arg catalyzed by arginase in M2 was mainly ornithine, which played a vital role in promoting tissue repair, which implemented angiogenesis timely and prevented hypertrophic scars. Mechanistically, FTA activated the cAMP signaling pathway combined with reducing inflammation and ameliorating angiogenesis, which resulted in excellent therapeutic effects on a DU mice model.

In Situ Cross-Linkable Hyaluronic-Ferulic Acid Conjugate Containing Bucladesine Nanoparticles Promotes Neural Regeneration after Spinal Cord Injury

Dysfunctional clinical outcomes following spinal cord injury (SCI) result from glial scar formation, leading to the inhibition of new axon growth and impaired regeneration. Nevertheless, nerve regeneration after SCI is possible, provided that the state of neuron development in the injured environment is improved. Hence, biomaterial-based therapy would be a promising strategy to endow a desirable environment for tissue repair. Herein, we designed a novel multifunctional injectable hydrogel with antioxidant, neuroprotective, and neuroregenerative effects. Bucladesine-encapsulated chitosan nanoparticles (BCS NPs) were first prepared and embedded in a matrix of thiol-functionalized hyaluronic acid modified with ferulic acid (HASH-FA). The target hydrogel (HSP-F/BCS) was then created through Michael-type addition between HASH-FA containing BCS NPs and four-arm polyethylene glycol-maleimide (4-Arm-PEG-Mal). The obtained hydrogel with shear thinning behavior showed viscoelastic and mechanical properties similar to the normal nerve tissue. FA conjugation significantly improved the antioxidant activity of HA, and suppressed intracellular ROS formation. In situ injection of the HSP-F/BCS hydrogel in a rat contusion model of SCI inhibited glial scar progression, reduced microglia/macrophage infiltration, promoted angiogenesis, and induced myelinated axon regeneration. As a result, a significant improvement in motor performance was observed compared to other experimental groups. Taken together, the HSP-F/BCS hydrogel developed in this study could be a promising system for SCI repair.

Signaling Pathways Associated with Chronic Wound Progression: A Systems Biology Approach

Previously we have shown that several oxidative stress-driven pathways in cutaneous chronic wounds are dysregulated in the first 48 h post-wounding. Here, we performed an RNASeq analysis of tissues collected up to day 20 after wounding, when we have determined full chronicity is established. Weighted Gene Correlation Network Analysis was performed in R segregating the genes into 14 modules. Genes in the modules significantly correlated (p < 0.05) to early and full chronicity were used for pathway analysis using pathfindR. In early chronicity, we observed enrichment of several pathways. Dysregulation of Ephrin/Eph signaling leads to growth cone collapse and impairs neuronal regeneration. Adra2b and Adra2a overexpression in early and full chronicity, respectively, decreased cAMP production and impaired re-epithelialization and granulation tissue formation. Several pathways involving a Smooth-muscle-actin (Acta1) were also enriched with Acta1 overexpression contributing to impaired angiogenesis. During full chronicity, the ‘JAK-STAT’ pathway was suppressed undermining host defenses against infection. Wnt signaling was also suppressed, impairing re-epithelialization and granulation tissue formation. Biomarkers of cancer such as overexpression of SDC1 and constitutive activation of ErbB2/HER2 were also identified. In conclusion, we show that during progression to full chronicity, numerous signaling pathways are dysregulated, including some related to carcinogenesis, suggesting that chronic wounds behave much like cancer. Experimental verification in vivo could identify candidates for treatment of chronic wounds.

Vascular Endothelial Repair and the Influence of Circulating Antiplatelet Drugs in a Carotid Coil Model

Background:

Clinicians may choose to administer antiplatelet medications to patients with cerebral aneurysms following endovascular coiling to prevent thrombus formation and vascular occlusion, if they fear a thrombus will form on the platinum wire where it diverges into the vessel from the aneurysm sac. However, the mechanism by which vascular endothelial cells repair a vessel in the living body in the event of a coil deviation and the effects of antiplatelet drugs on these cells have not been fully elucidated. We aimed to investigate the association between endothelial progenitor cells (EPCs) and endothelium formation at the surface of the platinum coils deployed in the carotid artery of rats, and to determine the effects of different antiplatelet drugs on this process.

Subjects and Methods:

We established an experimental model using normal and diabetic rats at 12 months of age. The diabetic rats were assigned to 4 different diet groups, distinguished by whether they were fed plain rat feed, or the same feed supplemented by 1 of 3 antiplatelet drugs (cilostazol, aspirin, or clopidogrel: all 0.1%) for 2 weeks, and the carotid artery was perforated by an embolization coil (“carotid coil model”). We monitored the process by which vascular endothelial cells formed the new endothelium on the surface of the coil by sampling and evaluating the region at 1, 2, and 4 weeks after placement. This repair process was also compared among 3 groups treated with different antiplatelet drugs (i.e. aspirin, clopidogrel, and cilostazol). One-way analysis of variance tests were performed to evaluate the differences in vascular thickness between groups, and P < .05 was considered statistically significant.

Results:

The diabetic rats showed delayed neoendothelialization and marked intimal hyperplasia. Cilostazol and clopidogrel effectively counteracted this delayed endothelial repair process. Flk1 immunostaining revealed greater expression in the diabetic rats administered cilostazol, second only to normal rats, suggesting that this agent acted to recruit EPCs.

Conclusion:

Neoendothelialization is delayed when vascular endothelial cells fail to function normally, which consequently leads to the formation of hyperplastic tissue. Cilostazol may remedy this dysfunction by recruiting EPCs to the site of injury.

Activity of the human immortalized endothelial progenitor cell line HEPC-CB.1 supporting in vitro angiogenesis

The human HEPC-CB.1 cell line with many characteristics of endothelial progenitor cells (EPC) was tested for its proangiogenic properties as a potentially therapeutic compound. HEPC-CB.1 cells’ potential to differentiate into endothelial cells was revealed after treating the cells with a mixture of ATRA, cAMP and VEGF, as shown by the reduced expression levels of CD133, CD271 and CD90 antigens, augmentation of CD146 and CD31, and a decrease in cell clonogenicity. The cooperation of HEPC-CB.1 with the endothelial cell line HSkMEC.2 resulted in the formation of a common network. Tube formation was significantly more effective when resulting from HEPC-CB.1 and HSkMEC.2 cell co-culture as compared to a monoculture of each cell line. The exocrine mechanism of HEPC-CB.1 and HSkMEC.2 cross talk by secreted factors was evidenced using the HEPC-CB.1 supernatant to increase the efficacy of HSkMEC.2 tube formation. The proangiogenic factors produced by HEPC-CB.1 were identified using cytokine antibody array. Out of 120 examined factors, the HEPC-CB.1 cell line produced 63, some with known angiogenic activity. As in vivo the angiogenic process occurs at low oxygen tension, it was observed that in hypoxia, the production of defined factors was augmented. The presented results demonstrate that HEPC-CB.1 cells are able to both cooperate and integrate in a newly formed network and produce factors that help the network formation. The results suggest that HEPC-CB.1 cells are indeed endothelial progenitors and may prove to be an effective tool in regenerative medicine.

Layer-by-layer self-assembly polyelectrolytes loaded with cyclic adenosine monophosphate enhances the osteo/odontogenic differentiation of stem cells from apical papilla

Cyclic adenosine monophosphate (cAMP) is a second messenger involved in the dental regeneration. However, efficient long-lasting delivery of cAMP that is sufficient to mimic the in vivo microenvironment remains a major challenge. Here, cAMP was loaded in stem cells from apical papilla (SCAPs) using layer-by-layer self-assembly with gelatin and alginate polyelectrolytes (LBL-cAMP-SCAPs). LBL-cAMP-SCAPs expressed cAMP and increased the phosphorylation level of cAMP-response element-binding protein (CREB) which were evaluated by immunofluorescence and western blotting (WB). Enzyme-linked immunosorbent assay (ELISA) demonstrated that a sustained release of cAMP and vascular endothelial growth factor (VEGF) were present up to 14 days. Scanning electron microscopy (SEM) found LBL-coated SCAPs exhibited a spheroid-like morphology. CCK8 and live/dead staining showed that LBL treatment had no significant effect on cell proliferation and viability. LBL-cAMP-SCAPs enhanced mineralized nodule formation and up-regulated the mRNA levels of the osteogenesis-related genes, as well as related transcription factor-2 protein level which were revealed by Alizarin red staining, RT-PCR and WB, respectively. In conclusion, LBL self-assembly loaded with cAMP promoted the osteo/odontogenic differentiation of SCAPs, thereby providing a potential strategy for bioactive molecular delivery in dental regeneration.

Targeting Cyclic AMP Signalling in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a major healthcare problem worldwide, representing one of the leading causes of cancer mortality. Since there are currently no predictive biomarkers for early stage diagnosis, HCC is detected only in advanced stages and most patients die within one year, as radical tumour resection is generally performed late during the disease. The development of alternative therapeutic approaches to HCC remains one of the most challenging areas of cancer. This review focuses on the relevance of cAMP signalling in the development of hepatocellular carcinoma and identifies the modulation of this second messenger as a new strategy for the control of tumour growth. In addition, because the cAMP pathway is controlled by phosphodiesterases (PDEs), targeting these enzymes using PDE inhibitors is becoming an attractive and promising tool for the control of HCC. Among them, based on current preclinical and clinical findings, PDE4-specific inhibitors remarkably demonstrate therapeutic potential in the management of cancer outcomes, especially as adjuvants to standard therapies. However, more preclinical studies are warranted to ascertain their efficacy during the different stages of hepatocyte transformation and in the treatment of established HCC.

CCL2-Mediated Reversal of Impaired Skin Wound Healing in Diabetic Mice by Normalization of Neovascularization and Collagen Accumulation

Patients with diabetes frequently present with complications such as impaired skin wound healing. Skin wound sites display a markedly enhanced expression of CCL2, a potent macrophage chemoattractant, together with macrophage infiltration during the early inflammatory phase in skin wound healing of healthy individuals, but the association of CCL2 with delayed skin wound healing in patients with diabetes remains elusive. In this study, we showed that, compared with control mice, mice with streptozotocin-induced diabetes displayed impaired healing after excisional skin injury, with decreased neovascularization, CCL2 expression, and macrophage infiltration. Compromised skin wound healing in mice with diabetes was reversed by the administration of topical CCL2 immediately after the injury, as evidenced by normalization of wound closure rates, neovascularization, collagen accumulation, and infiltration of macrophages expressing vascular endothelial growth factor, a potent angiogenic factor, and transforming growth factor-β. CCL2 treatment further increased the accumulation of endothelial progenitor cells at the wound sites of mice with diabetes and eventually accelerated neovascularization. Thus, the topical application of CCL2 can be an effective therapeutic option for the treatment of patients with diabetes with defective wound repair, promoting neovascularization and collagen accumulation at skin wound sites.

Melatonin protects endothelial progenitor cells against AGE-induced apoptosis via autophagy flux stimulation and promotes wound healing in diabetic mice

Wound healing is delayed in diabetic patients. Increased apoptosis and endothelial progenitor cell (EPC) dysfunction are implicated in delayed diabetic wound healing. Melatonin, a major secretory product of the pineal gland, promotes diabetic wound healing; however, its mechanism of action remains unclear. Here, EPCs were isolated from the bone marrow of mice. Treatment of EPCs with melatonin alleviated advanced glycation end product (AGE)-induced apoptosis and cellular dysfunction. We further examined autophagy flux after melatonin treatment and found increased light chain 3 (LC3) and p62 protein levels in AGE-treated EPCs. However, lysosome-associated membrane protein 2 expression was decreased, indicating that autophagy flux was impaired in EPCs treated with AGEs. We then evaluated autophagy flux after melatonin treatment and found that melatonin increased the LC3 levels, but attenuated the accumulation of p62, suggesting a stimulatory effect of melatonin on autophagy flux. Blockage of autophagy flux by chloroquine partially abolished the protective effects of melatonin, indicating that autophagy flux is involved in the protective effects of melatonin. Furthermore, we found that the AMPK/mTOR signaling pathway is involved in autophagy flux stimulation by melatonin. An in vivo study also illustrated that melatonin treatment ameliorated impaired wound healing in a streptozotocin-induced diabetic wound healing model. Thus, our study shows that melatonin protects EPCs against apoptosis and dysfunction via autophagy flux stimulation and ameliorates impaired wound healing in vivo, providing insight into its mechanism of action in diabetic wound healing.

Melatonin, a sleep-regulating hormone, may speed wound healing in patients with diabetes by protecting blood-borne wound-healing cells known as endothelial progenitor cells (EPCs). In diabetes, EPCs become damaged, lose their capacity to migrate to wounds and form new tissue, and die prematurely. Delayed healing can lead to ulcers, infection, and sometimes amputation. Melatonin has recently been reported to promote wound healing, but the mechanism remains unclear. Xiangyang Wang and Xiaolei Zhang at Wenzhou Medical University, China, and coworkers hypothesized that melatonin might protect EPCs from diabetes-induced damage. They found that melatonin improved EPCs’ ability to eliminate damaged components, allowing them to repair themselves and restoring their wound-healing function. In further experiments, diabetic mice treated with melatonin healed faster than untreated mice. These results may help improve treatments for complications of diabetes.

Monotropein promotes angiogenesis and inhibits oxidative stress-induced autophagy in endothelial progenitor cells to accelerate wound healing

Attenuating oxidative stress‐induced damage and promoting endothelial progenitor cell (EPC) differentiation are critical for ischaemic injuries. We suggested monotropein (Mtp), a bioactive constituent used in traditional Chinese medicine, can inhibit oxidative stress‐induced mitochondrial dysfunction and stimulate bone marrow‐derived EPC (BM‐EPC) differentiation. Results showed Mtp significantly elevated migration and tube formation of BM‐EPCs and prevented tert‐butyl hydroperoxide (TBHP)‐induced programmed cell death through apoptosis and autophagy by reducing intracellular reactive oxygen species release and restoring mitochondrial membrane potential, which may be mediated viamTOR/p70S6K/4EBP1 and AMPK phosphorylation. Moreover, Mtp accelerated wound healing in rats, as indicated by reduced healing times, decreased macrophage infiltration and increased blood vessel formation. In summary, Mtp promoted mobilization and differentiation of BM‐EPCs and protected against apoptosis and autophagy by suppressing the AMPK/mTOR pathway, improving wound healing in vivo. This study revealed that Mtp is a potential therapeutic for endothelial injury‐related wounds.

Harnessing cAMP signaling in musculoskeletal regenerative engineering

This paper reviews the most recent findings in the search for small molecule cyclic AMP analogues regarding their potential use in musculoskeletal regenerative engineering.

Inhibition of SDF-1 receptors CXCR4 and CXCR7 attenuates acute pulmonary inflammation via the adenosine A2B-receptor on blood cells

Acute pulmonary inflammation is characterized by migration of polymorphonuclear neutrophils into the different compartments of the lung. Recent studies showed evidence that the chemokine stromal cell-derived factor (SDF)-1 and its receptors CXCR4 and CXCR7 influence migration of immune cells and their activity was linked to adenosine concentrations. We investigated the particular role of CXCR4- and CXCR7-inhibition and the potential link to the adenosine A_2B-receptor, which plays an important anti-inflammatory role in the lung. After LPS-inhalation for 45 minutes, administration of the CXCR4-inhibitor (AMD3100) decreased transendothelial and transepithelial migration, whereas CXCR7-antagonism influenced epithelial migration exclusively. In A_2B−/− mice, no anti-inflammatory effects were detectible through either one of the agents. Using chimeric mice, we identified A_2B on hematopoietic cells to be crucial for these anti-inflammatory effects of CXCR4/7-inhibition. Both inhibitors decreased TNFα, IL6, CXCL1 and CXCL2/3 levels in the bronchoalveolar lavage of wild type mice, while not influencing the chemokine release in A_2B−/− mice. Inflammation augmented the expression of both receptors and their inhibition increased A_2B-levels upon inflammation. In vitro assays with human epithelium/endothelium confirmed our in vivo findings. During inflammation, inhibition of CXCR4- and CXCR7-receptors prevented microvascular permeability in wild type but not in A_2B−/− mice, highlighting the pivotal role of an active A_2B-receptor in this setting. The combination of both inhibitors had a synergistic effect in preventing capillary leakage. In conclusion, we determined the pivotal role of CXCR4- and CXCR7-inhibition in acute pulmonary inflammation, which depended on A_2B-receptor signalling.

Podoplanin expression in peritumoral keratinocytes predicts aggressive behavior in extramammary Paget's disease

BACKGROUND

Recent studies have demonstrated podoplanin expression in several tumors, which has been associated with lymph node metastasis and poor prognosis. Podoplanin expression in peritumoral cells such as cancer-associated fibroblasts also correlates with tumor progression in several cancers. However, podoplanin expression and its association with extramammary Paget's disease (EMPD) remain unclear.

OBJECTIVE

In this study, we examined whether the presence of podoplanin expression in tumor cells or peritumoral basal keratinocytes correlated with aggressive behavior in patients with EMPD and investigated the mechanisms of podoplanin-mediated tumor invasion in this disorder.

METHODS

Skin samples of 37 patients with EMPD were investigated by immunohistochemical analysis. The functions of podoplanin in keratinocytes were examined in vitro by RT-PCR and with invadopodia gelatin-degradation assays using HaCaT cells.

RESULTS

Podoplanin was not identified in tumor cells in all cases. Podoplanin expression in peritumoral basal keratinocytes was observed in 25 patients (67.6%). In in situ EMPD, 50% of cases (9 in 18) exhibited podoplanin-positive keratinocytes, whereas 84.2% (16 in 19) demonstrated positive staining in invasive EMPD (P<0.05). Podoplanin expression in peritumoral keratinocytes was also associated with tumor thickness (P<0.005). By immunohistochemical analysis, podoplanin-positive peritumoral keratinocytes were found to be negative for E-cadherin, one of the major adhesion molecules of keratinocytes, which might contribute to tumor invasion into the dermis through a crack in the basal cell layer induced by down-regulation of cell adhesion therein. We further found that podoplanin-positive keratinocytes exhibited invadopodia, which are thought to function in the migration of cancer cells through tissue barriers, indicating that podoplanin-positive peritumoral basal keratinocytes might assist tumor invasion by degrading the extracellular matrix.

CONCLUSION

The presence of podoplanin expression in peritumoral keratinocytes correlates with aggressive behavior in EMPD and might therefore serve as a useful prognostic marker for patients with EMPD.

Eicosanoids: Emerging contributors in stem cell-mediated wound healing

Eicosanoids are bioactive lipid products primarily derived from the oxidation of arachidonic acid (AA). The individual contributions of eicosanoids and stem cells to wound healing have been of great interest. This review focuses on how stem cells work in concert with eicosanoids to create a beneficial environment in the wound bed and in the promotion of wound healing. Stem cells contribute to wound healing through modulating inflammation, differentiating into skin cells or endothelial cells, and exerting paracrine effects by releasing various potent growth factors. Eicosanoids have been shown to stimulate proliferation, migration, homing, and differentiation of stem cells, all of which contribute to the process of wound healing. Increasing evidence has shown that eicosanoids improve wound healing through increasing stem cell densities, stimulating differentiation, and enhancing the angiogenic properties of stem cells. Chronic wounds have become a major problem in health care. Therefore, research regarding the effects of stem cells and eicosanoids in the promotion wound healing is of great importance.

Platelets Regulate the Migration of Keratinocytes via Podoplanin/CLEC-2 Signaling during Cutaneous Wound Healing in Mice

Podoplanin is an endogenous ligand for C-type lectin-like receptor 2 (CLEC-2), which is expressed on platelets. Recent evidence indicates that this specific marker of lymphatic endothelial cells is also expressed by keratinocytes at the edge of wounds. However, whether podoplanin or platelets play a role in keratinocyte activity during wound healing remains unknown. We evaluated the effect of podoplanin expression levels on keratinocyte motility using cultured primary normal human epidermal keratinocytes (NHEKs). Down-regulation of podoplanin in NHEKs via transfection with podoplanin siRNA inhibited their migration, indicating that podoplanin plays a mandatory role in this process. In addition, down-regulation of podoplanin was correlated with up-regulation of E-cadherin, suggesting that podoplanin-mediated stimulation of keratinocyte migration is associated with a loss of E-cadherin. Both the addition of platelets and treatment with CLEC-2 inhibited the migration of NHEKs. The down-regulation of RhoA activity and the up-regulation of E-cadherin in keratinocytes were also induced by CLEC-2. In conclusion, these results suggest that podoplanin/CLEC-2 signaling regulates keratinocyte migration via modulating E-cadherin expression through RhoA signaling. Altering the regulation of keratinocyte migration by podoplanin might be a novel therapeutic approach to improve wound healing.

Autologous circulating angiogenic cells treated with osteopontin and delivered via a collagen scaffold enhance wound healing in the alloxan-induced diabetic rabbit ear ulcer model

INTRODUCTION

Diabetic foot ulceration is the leading cause of amputation in people with diabetes mellitus. Peripheral vascular disease is present in the majority of patients with diabetic foot ulcers. Despite standard treatments there exists a high amputation rate. Circulating angiogenic cells previously known as early endothelial progenitor cells are derived from peripheral blood and support angiogenesis and vasculogenesis, providing a potential topical treatment for non-healing diabetic foot ulcers.

METHODS

A scaffold fabricated from Type 1 collagen facilitates topical cell delivery to a diabetic wound. Osteopontin is a matricellular protein involved in wound healing and increases the angiogenic potential of circulating angiogenic cells. A collagen scaffold seeded with circulating angiogenic cells was developed. Subsequently the effect of autologous circulating angiogenic cells that were seeded in a collagen scaffold and topically delivered to a hyperglycemic cutaneous wound was assessed. The alloxan-induced diabetic rabbit ear ulcer model was used to determine healing in response to the following treatments: collagen seeded with autologous circulating angiogenic cells exposed to osteopontin, collagen seeded with autologous circulating angiogenic cells, collagen alone and untreated wound. Stereology was used to assess angiogenesis in wounds.

RESULTS

The cells exposed to osteopontin and seeded on collagen increased percentage wound closure as compared to other groups. Increased angiogenesis was observed with the treatment of collagen and collagen seeded with circulating angiogenic cells.

CONCLUSIONS

These results demonstrate that topical treatment of full thickness cutaneous ulcers with autologous circulating angiogenic cells increases wound healing. Cells exposed to the matricellular protein osteopontin result in superior wound healing. The wound healing benefit is associated with a more efficient vascular network. This topical therapy provides a potential novel therapy for the treatment of non-healing diabetic foot ulcers in humans.

The stable cyclic adenosine monophosphate analogue, dibutyryl cyclo-adenosine monophosphate (bucladesine), is active in a model of acute skin inflammation

Anti-inflammatory therapeutic options for the topical treatment of skin diseases with inflammatory or allergic contribution are mostly limited to topical glucocorticoids and calcineurin inhibitors. Both compound classes induce adverse effects. Elevation of intracellular cyclic adenosine monophosphate (cAMP) by inhibition of phosphodiesterase 4 was shown to induce potent anti-inflammatory effects, but the safety profile of currently available compounds is not sufficient. A different approach to increase intracellular cAMP is the substitution of chemically stabilized cAMP analogues. Bucladesine is a stabilized cAMP analogue with an excellent safety profile which had been marketed as topical treatment of impaired wound healing. In the current study, a novel water free emulsion containing bucladesine was evaluated for anti-inflammatory effects. In the arachidonic acid induced ear oedema model in mice, single or multiple administration of an emulsion containing 1.5% was capable of significantly reducing the inflammatory oedema. The data indicate that bucladesine represents an interesting treatment option for skin diseases where an anti-inflammatory activity is indicated. Due to the established clinical safety, this agent may bridge the gap between potent agents such as glucocorticoids or calcineurin inhibitors and emollients without active compounds.

Influence of various treatments including povidone-iodine and healing stimulatory reagents in a rabbit ear wound model

Selecting an appropriate treatment for a given case of skin wound is crucial for inducing optimal healing. We used an animal model developed from normal rabbit ears in order to assess the efficacy of treatments for skin wounds with or without a wet dressing, anti microbial reagent or topical wound-stimulatory reagents. The degree of healing in each group was evaluated and compared using four histological parameters: (i) degree of reepithelialisation, (ii) amount of granulation tissue formation, and (iii) the number of capillary lumens and (iv) fibroblasts in the granulation tissue. Treatment using wet dressings resulted in an increase in capillary number compared with the open dry wound. Although the retention of povidone-iodine (PI) in wound tissue after application significantly inhibited reepithelialisation (P < 0.05), rinsing PI off with saline was comparable in effect to using only a wet dressing. The three topical reagents, namely, basic fibroblast growth factor, prostaglandin E1 and dibutyryl cyclic adenosine monophosphate, significantly improved reepithelialisation (P < 0.05). In conclusion, wounds should be kept hydrated by applying topical reagents. If there are any signs of bacterial infection, PI can be applied and rinsed later with saline in order to minimise its cytotoxic effects.

Topical simvastatin accelerates wound healing in diabetes by enhancing angiogenesis and lymphangiogenesis

Impaired wound healing is a major complication of diabetes. Recent studies have reported reduced lymphangiogenesis and angiogenesis during diabetic wound healing, which are thought to be new therapeutic targets. Statins have effects beyond cholesterol reduction and can stimulate angiogenesis when used systemically. However, the effects of topically applied statins on wound healing have not been well investigated. The present study tested the hypothesis that topical application of simvastatin would promote lymphangiogenesis and angiogenesis during wound healing in genetically diabetic mice. A full-thickness skin wound was generated on the back of the diabetic mice and treated with simvastatin or vehicle topically. Simvastatin administration resulted in significant acceleration of wound recovery, which was notable for increases in both angiogenesis and lymphangiogenesis. Furthermore, simvastatin promoted infiltration of macrophages, which produced vascular endothelial growth factor C in granulation tissues. In vitro, simvastatin directly promoted capillary morphogenesis and exerted an antiapoptotic effect on lymphatic endothelial cells. These results suggest that the favorable effects of simvastatin on lymphangiogenesis are due to both a direct influence on lymphatics and indirect effects via macrophages homing to the wound. In conclusion, a simple strategy of topically applied simvastatin may have significant therapeutic potential for enhanced wound healing in patients with impaired microcirculation such as that in diabetes.

Cyclic nucleotide compartmentalization: contributions of phosphodiesterases and ATP-binding cassette transporters

Cyclic nucleotides [e.g., cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP)] are ubiquitous second messengers that affect multiple cell functions from maturation of the egg to cell division, growth, differentiation, and death. The concentration of cAMP can be regulated by processes within membrane domains (local regulation) as well as throughout a cell (global regulation). The phosphodiesterases (PDEs) that degrade cAMP have well-known roles in both these processes. It has recently been discovered that ATP-binding cassette (ABC) transporters contribute to both local and global regulation of cAMP. This regulation may require the formation of macromolecular complexes. Some of these transporters are ubiquitously expressed, whereas others are more tissue restricted. Because some PDE inhibitors are also ABC transporter inhibitors, it is conceivable that the therapeutic benefits of their use result from the combined inhibition of both PDEs and ABC transporters. Deciphering the individual contributions of PDEs and ABC transporters to such drug effects may lead to improved therapeutic benefits.

Topical application of ex vivo expanded endothelial progenitor cells promotes vascularisation and wound healing in diabetic mice

Impaired wound healing leading to skin ulceration is a serious complication of diabetes and may be caused by defective angiogenesis. Endothelial progenitor cells (EPCs) can augment neovascularisation in the ischaemic tissue. Experiments were performed to test the hypothesis that locally administered EPCs can promote wound healing in diabetes. Full-thickness skin wounds were created on the dorsum of diabetic mice. EPCs were obtained from bone marrow mononuclear cells (BMMNCs) and applied topically to the wound immediately after surgery. Vehicle and non-selective BMMNCs were used as controls. Wound size was measured on days 5, 10 and 14 after treatment, followed by resection, histological analysis and quantification of vascularity. Topical application of EPCs significantly promoted wound healing, as assessed by closure rate and wound vascularity. Immunostaining revealed that transplanted EPCs induced increased expression of vascular endothelial growth factor and basic fibroblast growth factor. Few EPCs were observed in the neovasculature based on in vivo staining of the functional vasculature. Ex vivo expanded EPCs promote wound healing in diabetic mice via mechanisms involving increased local cytokine expression and enhanced neovascularisation of the wound. This strategy exploiting the therapeutic capacity of autologously derived EPCs may be a novel approach to skin repair in diabetes.

CXCR4 antagonist AMD3100 accelerates impaired wound healing in diabetic mice

The antagonism of CXC-chemokine receptor 4 (CXCR4) with AMD3100 improves cardiac performance after myocardial infarction by augmenting the recruitment of endothelial progenitor cells (EPCs) from the bone marrow to the regenerating vasculature. We investigated whether AMD3100 may accelerate diabetes-impaired wound healing through a similar mechanism. Skin wounds were made on the backs of leptin-receptor–deficient mice and treated with AMD3100 or saline. Fourteen days after treatment, wound closure was significantly more complete in AMD3100-treated mice (AMD3100: 87.0±2.6%, Saline: 33.1±1.8%; P<0.0001) and was accompanied by greater collagen-fiber formation, capillary density, smooth-muscle-containing vessel density, and monocyte/macrophage infiltration. On day 7 after treatment, AMD3100 was associated with higher circulating EPC and macrophage counts and with significantly upregulated mRNA levels of stromal-cell–derived factor 1 and platelet-derived growth-factor B in the wound bed. AMD3100 also promoted macrophage proliferation and phagocytosis and the migration and proliferation of diabetic mouse primary dermal fibroblasts and 3T3 fibroblasts, which express very little CXCR4. In conclusion, a single topical application of AMD3100 promoted wound healing in diabetic mice by increasing cytokine production, mobilizing bone-marrow EPCs, and enhancing the activity of fibroblasts and monocytes/macrophages, thereby increasing both angiogenesis and vasculogenesis. Not all of the AMD3100-mediated effects evolved through CXCR4 antagonism.

Cilostazol enhances neovascularization in the mouse hippocampus after transient forebrain ischemia

Cilostazol is known to be a specific type III phosphodiesterase inhibitor, which promotes increased intracellular cAMP levels. We assessed the effect of cilostazol on production of angioneurins and chemokines and recruitment of new endothelial cells for vasculogenesis in a mouse model of transient forebrain ischemia. Pyramidal cell loss was prominently evident 3-28 days postischemia, which was markedly ameliorated by cilostazol treatment. Expression of angioneurins, including endothelial nitric oxide synthase, vascular endothelial growth factor, and brain-derived neurotrophic factor, was up-regulated by cilostazol treatment in the postischemic hippocampus. Cilostazol also increased Sca-1/vascular endothelial growth factor receptor-2 positive cells in the bone marrow and circulating peripheral blood and the number of stromal cell-derived factor-1alpha-positive cells in the molecular layer of the hippocampus, which colocalized with CD31. CXCR4 chemokine receptors were up-regulated by cilostazol in mouse bone marrow-derived endothelial progenitor cells, suggesting that cilostazol may be important in targeting or homing in of bone marrow-derived stem cells to areas of injured tissues. CD31-positive cells were colocalized with almost all bromodeoxyuridine-positive cells in the molecular layer, indicating stimulation of endothelial cell proliferation by cilostazol. These data suggest that cilostazol markedly enhances neovascularization in the hippocampus CA1 area in a mouse model of transient forebrain ischemia, providing a beneficial interface in which both bone marrow-derived endothelial progenitor cells and angioneurins influence neurogenesis in injured tissue. (c) 2010 Wiley-Liss, Inc.

Systemic transplantation of progenitor cells accelerates wound epithelialization and neovascularization in the hairless mouse ear wound model

BACKGROUND

Impaired wound healing due to local injury, infection, or systemic diseases, such as diabetes, is a major clinical problem. Recent studies have shown that endothelial progenitor cells (EPC) isolated from peripheral blood, bone marrow, as well as the spleen accumulate in granulation tissue at the site of neovascularization, causing secretion of growth factors and cytokines and thus accelerating wound healing.

MATERIALS AND METHODS

In the present study, we transplanted systemic EPC and then measured epithelialization and neovascularization in the hairless mouse ear wound model.

RESULTS

Systemic EPC transplantation significantly accelerated epithelialization and neovascularization compared with control wounds receiving phosphate-buffered saline without calcium and magnesium (PBS). The EPC group had significantly higher vascular density than did the PBS-treated group as determined by immunohistochemistry for CD31 and CD90. Fluorescence microscopy revealed accumulation "homing" of the transplanted EPC at the sites of neovascularization in the granulation tissue throughout healing. Furthermore, transplantation of EPC also increased the expression of the angiogenic cytokine stromal cell-derived factor 1α (SDF1α).

CONCLUSIONS

This appears to be the first demonstration of EPC recruitment to the site of wound neovascularization throughout the healing process. These findings demonstrate that transplanting systemic EPC into "normal" healing wounds promotes epithelialization and neovascularization and thus could be an useful method for accelerating wound healing.

Rho GTPase, Rac1, regulates Skp2 levels, vascular smooth muscle cell proliferation, and intima formation in vitro and in vivo

AIMS

Vascular smooth muscle cell (VSMC) proliferation contributes to intima formation after angioplasty or venous by-pass grafting, and during atherosclerosis. VSMC proliferation requires degradation of p27(Kip1) promoted by S-phase kinase-associated protein-2 (Skp2), an F-box protein component of the Skp-Cullin-F-box(Skp2) ubiquitin-ligase. We investigated the role of Rac(1) in the regulation of Skp2 in rat VSMC.

METHODS AND RESULTS

Rat carotid balloon injury increased Rac(1) activity. Rho GTPase inhibition with Clostridium difficile Toxin B or specific Rac(1) inhibition with adenovirus-mediated expression of dominant-negative Rac(1) reduced Skp2 levels, and VSMC proliferation in vitro and intima formation in vivo following carotid balloon injury. Inhibition of Skp2 expression and proliferation by dominant-negative Rac(1) was reversed by exogenous Skp2. Elevation of endogenous adenosine 3',5'-cyclic monophosphate (cAMP) with forskolin-inhibited Rac(1) activity, reduced Skp2, increased p27(Kip1) and inhibited VSMC proliferation, effects that were reversed by constitutively active Rac(1). These effects were independent of Rac(1) Cdc42/Rac interactive binding (CRIB)-domain effector proteins but associated with Rac(1)-dependent actin polymerization.

CONCLUSION

Rac(1) activity regulates VSMC proliferation by controlling Skp2 levels. Activation of Rac(1) induced by balloon injury in vivo increases Skp2 levels, which promotes VSMC proliferation and intima formation. Inhibition of this novel pathway underlies the negative effects of cAMP on VSMC proliferation.

Endothelial progenitor cells for the treatment of diabetic vasculopathy: panacea or Pandora's box?

The discovery of endothelial progenitor cell (EPC) a decade ago has refuted the previous belief that vasculogenesis only occurs during embryogenesis. The reduced circulating concentration of EPCs is a surrogate marker of endothelial function and has been implicated in the pathogenesis of many vascular diseases. To date, the therapeutic benefit of neovascularization in ischaemic conditions in a non-diabetic setting has been demonstrated. This article aims to review the biology of EPCs in the diabetic setting with special emphasis on the effects of cardiovascular risk factor modification on EPC phenotype and methods to reverse or augment EPC dysfunction. The potential of the use of EPCs in the treatment of the diabetic vascular dysfunction will also be discussed.

Biphasic expression of stromal cell-derived factor-1 during human wound healing

BACKGROUND

Chemokines tightly regulate the spatial and temporal infiltration of invading leucocyte subsets during wound healing. Stromal cell-derived factor-1 (SDF-1/CXCL12) is a homeostatic chemokine with multiple functions; its role during cutaneous wound healing, however, needs to be explored.

OBJECTIVES

To elucidate expression of the multifunctional CXC chemokine SDF-1/CXCL12 during human wound healing.

METHODS

Skin biopsies were obtained from 14 volunteers between 1 and 21 days after incisional wounding and processed for in situ hybridization and immunohistochemistry.

RESULTS

We analysed the spatial and temporal distribution of SDF-1/CXCL12 after artificial wounding and detected a complete downregulation at both the mRNA and the protein level within the fibrous stroma that replaces the initial wound defect. However, increased levels of SDF-1/CXCL12 were observed at the wound margins. Focusing on mediators regulating SDF-1/CXCL12 expression in vitro we realized that both tumour necrosis factor-alpha and interferon-gamma downregulated its expression in human dermal microvascular endothelial cells and fibroblasts.

CONCLUSIONS

Our data suggest that SDF-1/CXCL12 is tightly regulated during wound repair. Increased expression at the wound margin may contribute to the accumulation of endothelial progenitor cells, thus accelerating neovascularization.

Uric acid heralds ischemic tissue injury to mobilize endothelial progenitor cells

Understanding the nature of endogenous mechanisms for mobilization of stem/progenitor cells is predicated on the identification of injury-induced substances that are released from a damaged organ and capable of producing a distant effect. Although different substances that mobilize endothelial progenitor cells (EPCs) have been proposed, their potential to signal injury and afford postischemic renoprotection and repair remains obscure. Uric acid (UA) is consistently overproduced by ischemic tissues and has been shown to exert immunomodulatory functions. It was hypothesized that UA and/or its precursors might serve as injury signals that are capable of mobilizing EPCs in acute renal ischemia. Indeed, FVB/NJ mice that were subjected to acute renal ischemia showed a transient surge in UA level in the peripheral blood. Single-dose treatment with UA, as well as acute hyperuricemia induced by the inhibition of uricase, caused a robust mobilization of EPCs, whereas administration of adenosine or inosine seemed to lack this effect. Moreover, pretreatment of mice with a single dose of UA afforded significant renoprotection against ischemic injury. In animals with chronic hyperuricemia (induced by continuous 2-wk treatment with a uricase inhibitor oxonic acid), EPC mobilization was blunted and renoprotective effects were absent. In conclusion, acute elevation of UA acts as "physiologic," fast-acting endogenous mediator of EPC mobilization and renoprotection, consistent with its novel function in pharmacologic preconditioning. Both of these actions are lacking in mice with chronic hyperuricemia. In summary, a transient surge in UA concentration may serve as a universal herald of tissue injury to accelerate the recruitment of EPCs.

Cilostazol, a phosphodiesterase 3 inhibitor, protects mice against acute and late ischemic brain injuries

Cilostazol, a selective inhibitor of phosphodiesterase 3, exerts neuroprotective effects on acute brain injury after cerebral ischemia in rats. However, it is unknown whether cilostazol affects the subacute or chronic ischemic injury. In the present study, we evaluated the dose- and time-dependent effects of cilostazol on acute ischemic brain injury and the long-lasting effect on the late (subacute/chronic) injury in mice with focal cerebral ischemia induced by transient middle cerebral artery occlusion. We found that pre-treatment of cilostazol (injected i.p. at 30 min before ischemia) significantly ameliorated the acute injury 24 h after ischemia, and the effective doses were 3-10 mg/kg. The post-treatment of cilostazol (10 mg/kg) was effective on the acute injury when it was injected 1 and 2 h after ischemia. In addition, for the late injury, post-treatment of cilostazol (10 mg/kg, i.p., for 7 consecutive days after ischemia) attenuated neurological dysfunctions, brain atrophy and infarct volume. It also inhibited astrocyte proliferation/glial scar formation and accelerated the angiogenesis in the ischemic boundary zone 7 and 28 days after ischemia. Thus, we conclude that cilostazol protects against not only the acute injury, but also the late injury in mice with focal cerebral ischemia; especially it can modify brain remodeling, astrogliosis and angiogenesis.