The microcirculation in acute murine cutaneous incisional wounds shows a spatial and temporal variation in the functionality of vessels

A biphasic drug-releasing microneedle with ROS scavenging and angiogenesis for the treatment of diabetic ulcers

Diabetic ulcers are one of the common complications in diabetic patients. Delayed wound healing is associated with persistent pro-inflammatory M1 polarization, reduced angiogenesis and increased reactive oxygen species (ROS) in the microenvironment. Wound healing consists of multiple phases and therefore requires treatment tailored to each phase. In this study, a biphasic drug-releasing microneedle (MN) was fabricated to achieve early ROS scavenging and late accelerated angiogenesis to promote wound healing. Vascular endothelial growth factor (VEGF) was first encapsulated in methacryloylated sulfonated chitosan (SCSMA) microspheres (V@MP), and then V@MP was loaded into hyaluronic acid (HA) microneedles along with cerium dioxide nanoparticles (CONPs). Rapid dissolution of HA rapidly releases the CONPs to clear ROS, whereas the V@MP stays in the wound. SCSMA slow degradation prolongs the release of VEGF, thereby promoting angiogenesis. In vitro and in vivo studies have shown that this biphasic drug-releasing smart microneedle improves cell proliferation and migration, effectively scavenges ROS, promotes angiogenesis and tissue regeneration, and synergistically promotes M2 macrophage polarization. It provides a new delivery mode for nano-enzymes and growth factors that could be multifunctional and synergistic in the treatment of diabetic ulcers. STATEMENT OF SIGNIFICANCE: In our study, we present a microneedle (V@MP/C@MN) that can release drugs biphasically, which showed good repair ability in diabetic ulcer model. Large amounts of CONPs were rapidly released to alleviate oxidative stress during the inflammation of the wound, and V@MP stayed in the wound for a long period of time to release VEGF and promote angiogenesis in the late stage of wound healing. The results indicated that V@MP/C@MN could promote cell proliferation and migration, effectively scavenge ROS, promote angiogenesis and tissue regeneration, and synergistically promote M2 macrophage polarization, which could play a multifunctional and synergistic role in the treatment of diabetic ulcers.

Angiogenesis in Wound Repair: Too Much of a Good Thing?

Angiogenesis, or the growth of new blood vessels from the preexisting vasculature, is a visible and important component of wound repair. When tissue damage occurs, disruption of the vasculature structure leads to hypoxia. The restoration of normoxia is essential for appropriate and durable tissue repair. Angiogenesis in wounds is regulated by endogenous proangiogenic mediators, which cause rapid growth of a new vascular bed that is much denser than that of normal tissue. Such rapid growth of the capillary bed results in capillaries that are abnormal, and the newly formed vessels are tortuous, dilated, and immature. During wound resolution, this substantial neocapillary bed is pruned back to normal density with attendant maturation. Many poorly healing wounds, including nonhealing ulcers and scars, exhibit an aberrant angiogenic response. The fine-tuning of capillary regrowth in wounds is an area of significant therapeutic potential.

Effect of Polymeric Nanoparticles with Entrapped Fish Oil or Mupirocin on Skin Wound Healing Using a Porcine Model

The utilization of poly(lactic-co-glycolic) acid (PLGA) nanoparticles (NPs) with entrapped fish oil (FO) loaded in collagen-based scaffolds for cutaneous wound healing using a porcine model is unique for the present study. Full-depth cutaneous excisions (5 × 5 cm) on the pig dorsa were treated with pure collagen scaffold (control, C), empty PLGA NPs (NP), FO, mupirocin (MUP), PLGA NPs with entrapped FO (NP/FO) and PLGA NPs with entrapped MUP (NP/MUP). The following markers were evaluated on days 0, 3, 7, 14 and 21 post-excision: collagen, hydroxyproline (HP), angiogenesis and expressions of the COX2, EGF, COL1A1, COL1A3, TGFB1, VEGFA, CCL5 and CCR5 genes. The hypothesis that NP/FO treatment is superior to FO alone and that it is comparable to NP/MUP was tested. NP/FO treatment increased HP in comparison with both FO alone and NP/MUP (day 14) but decreased (p < 0.05) angiogenesis in comparison with FO alone (day 3). NP/FO increased (p < 0.05) the expression of the CCR5 gene (day 3) and tended (p > 0.05) to increase the expressions of the EGF (day 7, day 14), TGFB1 (day 21) and CCL5 (day 7, day 21) genes as compared with NP/MUP. NP/FO can be suggested as a suitable alternative to NP/MUP in cutaneous wound treatment.

Transforming growth factor beta-1 and vascular endothelial growth factor in the recovery and formation of skin scars

Relevance. Scars are multi-tissue structures that significantly reduce the quality of life of the young, able-bodied population. The most socially significant variants are represented by hypertrophic and keloid postoperative scars and scars after burns, atrophic scars after acne vulgaris and striae. Growth factors, which are also used for their treatment, play a significant role in their formation and progression. The aim of this work is to summarize data on the participation of growth factors (transforming growth factor beta-1 and vascular endothelial growth factor) in the formation of a hypertrophic or atrophic scar. Materials and Methods. The study of literary sources of scientometric scientific bases was carried out. Results and Discussion . The study showed that the duration of the scarring phases preceding it is of great importance in scar formation, their prolongation leads to chronic inflammation and the attachment of an autoimmune component, an increase in the number of myofibroblasts due to inhibition of apoptosis and an increase in the synthesis of intercellular substance and immature forms of collagen, as well as thinning of the epidermis over scar. Growth factors such as growth factor beta-1 and vascular endothelial growth factor are capable of shifting the balance of these two main pathways or towards proliferative processes, contributing to an increase in the number of blood vessels in the hemomicrocirculatory bed, the number of mast cells and total cellularity, as well as, in some cases, the synthesis of keloid - that is, the formation of a hypertrophic or keloid scar. On the contrary, the prevalence of inflammatory processes leads to a decrease in cellularity, a decrease in blood vessels and intercellular substance, as well as damage to elastin and collagen fibers, forming the phenotype of an atrophic scar or striae. Conclusion. Growth factors play a key role in scar formation, contributing to an increase in the number of blood vessels in the hemomicrocirculatory bed, the number of mast cells and total cellularity, as well as, in some cases, the synthesis of keloid - that is, the formation of a hypertrophic or keloid scar.

Phagocytosis of apoptotic endothelial cells reprograms macrophages in skin wounds

In healing wounds, the regression of blood vessels during the resolution phase creates a significant number of apoptotic endothelial cells (ApoECs). Surprisingly few studies have investigated the fate of apoECs in wounds, or the consequence of their removal. The current study employed both in vitro and in vivo models to investigate if macrophages ingest apoECs and to determine if such phagocytosis alters macrophage phenotype. To examine the capability of macrophages to ingest apoECs in in vivo wounds, pHrodo green labeled apoECs were injected into skin wounds 6 days after injury. The results demonstrated that 2.2% of macrophages in the wounds had engulfed apoECs 24 hours after injection. Macrophages that had engulfed apoECs expressed the markers CD80 (100%), CD86 (93.8%), and CD163 (22.8%), while no expression of CD206 marker was observed. In in vitro studies, 76.1% and 81.1% of PMA differentiated THP-1 macrophages engulfed apoECs at 6 and 24 hours, respectively. mRNA expression levels of IL-1β, iNOS, and TGF-β1 decreased in THP-1 macrophages after exposure to apoECs, while the expression of IL-6 increased. THP-1 macrophages that were incubated with apoECs for 6hours expressed CD80 (30.2%), CD163 (62.9%), and CD206 (45.3%), while expression levels in untreated group were 0.5%, 45.0%, and 2.4%, respectively. Taken together, our studies showed that macrophages phagocytize dermal apoECs both in vitro and in vivo. The engulfment of apoECs leads to a unique macrophage phenotype, which has characteristics of both M1 and M2 macrophage phenotypes. These findings provide a new mechanism by which macrophage phenotypes can be modified during wound resolution.

Direct current electric field regulates endothelial permeability under physiologically relevant fluid forces in a microfluidic vessel bifurcation model

Previous in vitro studies have reported on the use of direct current electric fields (DC-EFs) to regulate vascular endothelial permeability, which is important for tissue regeneration and wound healing. However, these studies have primarily used static 2D culture models that lack the fluid mechanical forces associated with blood flow experienced by endothelial cells (ECs) in vivo. Hence, the effect of DC-EF on ECs under physiologically relevant fluid forces is yet to be systematically evaluated. Using a 3D microfluidic model of a bifurcating vessel, we report the role of DC-EF on regulating endothelial permeability when co-applied with physiologically relevant fluid forces that arise at the vessel bifurcation. The application of a 70 V m-1 DC-EF simultaneously with 1 μL min-1 low perfusion rate (generating 3.8 dyn cm-2 stagnation pressure at the bifurcation point and 0.3 dyn cm-2 laminar shear stress in the branched vessel) increased the endothelial permeability 7-fold compared to the static control condition (i.e., without flow and DC-EF). When the perfusion rate was increased to 10 μL min-1 (generating 38 dyn cm-2 stagnation pressure at the bifurcation point and 3 dyn cm-2 laminar shear stress in the branched vessel) while maintaining the same electrical stimulation, a 4-fold increase in endothelial permeability compared to the static control was observed. The lower increase in endothelial permeability for the higher fluid forces but the same DC-EF suggests a competing role between fluid forces and the applied DC-EF. Moreover, the observed increase in endothelial permeability due to combined DC-EF and flow was transient and dependent on the Akt signalling pathway. Collectively, these findings provide significant new insights into how the endothelium serves as an electro-mechanical interface for regulating vessel permeability.

Vascularity and Thickness Changes in Immature Hypertrophic Scars Treated With a Pulsed Dye Laser

BACKGROUND AND OBJECTIVES

Growth of capillaries is an essential process after a dermal injury. An immature scar with robust growth of capillaries tends to be hypertrophic. Pulsed dye laser (PDL) causes damage to microvascular structures and is increasingly used for early erythematous scars to limit scar growth. To have a better understanding of the impact of PDL on scar vascularity and to optimize the clinical use of PDL for managing hypertrophic scars, this study aimed to explore changes in scar erythema, blood perfusion, and thickness of immature hypertrophic scars in Asian patients who received PDL treatments at an early stage.

STUDY DESIGN/MATERIALS AND METHODS

This was a 3-month, assessor-blinded, clinical study. There were two groups of patients, the PDL group and the control group, who had hypertrophic scars less than 1-year post-injury. Patients in the PDL group received three PDL sessions at 4-week intervals. A total of three assessments were performed, at baseline, 1 and 3 months, consisting of the Patient and Observer Scar Assessment Scale (POSAS) and objective measurements of scar erythema, blood perfusion, and scar thickness.

RESULTS

A total of 45 patients were enrolled, 22 in the PDL group and 23 in the control group. After the 3-month treatment, parameters of scar vascularity (P = 0.003), pigmentation (P = 0.026), color (P < 0.001), thickness (P < 0.05), and overall scores (P < 0.01) on the POSAS significantly decreased in the PDL group. Moreover, objective measurements of scar erythema and blood perfusion showed significant improvements in the PDL group (P = 0.009 and P = 0.022, respectively) but not in the control group (P = 0.296 and P = 0.115, respectively). A stable scar thickness was maintained in the PDL group from baseline to 3 months (0.21 cm vs. 0.22 cm, P > 0.05), whereas scar thickness significantly increased in the control group (0.22 cm vs. 0.32 cm, P < 0.01).

CONCLUSION

Use of PDL at an early stage controls vascularity of immature hypertrophic scar by improving its poor blood perfusion that further limits scar thickness growth and promotes scar maturation. Lasers Surg. Med. 00:00-00, 2020. © 2020 Wiley Periodicals LLC.

Limiting angiogenesis to modulate scar formation

Angiogenesis, the process of new blood vessel formation from existing blood vessels, is a key aspect of virtually every repair process. During wound healing an extensive, but immature and leaky vascular plexus forms which is subsequently reduced by regression of non-functional vessels. More recent studies indicate that uncontrolled vessel growth or impaired vessel regression as a consequence of an excessive inflammatory response can impair wound healing, resulting in scarring and dysfunction. However, in order to elucidate targetable factors to promote functional tissue regeneration we need to understand the molecular and cellular underpinnings of physiological angiogenesis, ranging from induction to resolution of blood vessels. Especially for avascular tissues (e.g. cornea, tendon, ligament, cartilage, etc.), limiting rather than boosting vessel growth during wound repair potentially is beneficial to restore full tissue function and may result in favourable long-term healing outcomes.

Anisotropic Biomimetic Silk Scaffolds for Improved Cell Migration and Healing of Skin Wounds

Improved and more rapid healing of full-thickness skin wounds remains a major clinical need. Silk fibroin (SF) is a natural protein biomaterial that has been used in skin repair. However, there has been little effort aimed at improving skin healing through tuning the hierarchical microstructure of SF-based matrices and introducing multiple physical cues. Recently, enhanced vascularization was achieved with SF scaffolds with nanofibrous structures and tunable secondary conformation of the matrices. We hypothesized that anisotropic features in nanofibrous SF scaffolds would promote cell migration, neovascularization, and tissue regeneration in wounds. To address this hypothesis, SF nanofibers were aligned in an electric field to form anisotropic porous scaffolds after lyophilization. In vitro and in vivo studies indicated good cytocompatibility, and improved cell migration and vascularization than nanofibrous scaffolds without these anisotropic features. These improvements resulted in more rapid wound closure, tissue ingrowth, and the formation of new epidermis, as well as higher collagen deposition with a structure similar to the surrounding native tissue. The new epidermal layers and neovascularization were achieved by day 7, with wound healing complete by day 28. It was concluded that anisotropic SF scaffolds alone, without a need for growth factors and cells, promoted significant cell migration, vascularization, and skin regeneration and may have the potential to effectively treat dermal wounds.

Modelling skin wound healing angiogenesis: A review

The occurrence of wounds is a main health concern in Western society due to their high frequency and treatment cost. During wound healing, the formation of a functional blood vessel network through angiogenesis is an essential process. Angiogenesis allows the reestablishment of the normal blood flow, the sufficient exchange of oxygen and nutrients and the removal of metabolic waste, necessary for cell proliferation and viability. Mathematical and computational models provide new tools to improve the healing process. In fact, over the last thirty years, in silico models have been continuously formulated to describe the effect of several biological and mechanical factors in angiogenesis during wound healing. Additionally, with different levels of complexity, these models allow coupling the human skin structure, to distinct cell types and growth factors, to study extracellular matrix composition and to understand its deformation. This paper discusses how in silico models, which are more economical and less time-consuming comparatively to laboratory methodologies, can help test new strategies to promote/optimize angiogenesis. The continuum, cell-based and hybrid mathematical models of wound healing angiogenesis are reviewed in the present paper, in order to identify possible improvements. Accordingly, the development of higher dimension models incorporating multiscale analysis at molecular, cellular and tissue level remains a challenge that future models should consider.

VEGF Receptor-2 Activation Mediated by VEGF-E Limits Scar Tissue Formation Following Cutaneous Injury

Objective: Vascular endothelial growth factor (VEGF) family members are critical regulators of tissue repair and depending on their distinct pattern of receptor specificity can also promote inflammation and scarring. This study utilized a receptor-selective VEGF to examine the role of VEGF receptor (VEGFR)-2 in scar tissue (ST) formation. Approach: Cutaneous skin wounds were created in mice using a 4 mm biopsy punch and then treated until closure with purified VEGF-E derived from orf virus stain NZ-2. Tissue samples were harvested to measure gene expression using quantitative PCR and to observe ST formation through histological examination and changes in cell populations by immunofluorescence. Results: VEGFR-2-activation with VEGF-E increased expression of anti-inflammatory cytokine interleukin (IL)-10 and reduced macrophage infiltration and myofibroblast differentiation in wounded skin compared with controls. VEGF-E treatment also increased microvascular density and improved pericyte coverage of blood vessels in the healing wounds. The ST that formed following treatment with VEGF-E was reduced in size and showed improved collagen structure. Innovation: The role of VEGFR-2 activation in wound epithelialization and angiogenesis is well established; but its contribution to ST formation is unclear. This study tests the effect of a selective VEGFR-2 activation on ST formation following cutaneous wounding in a murine model. Conclusion: VEGFR-2 stimulation can enhance the quality of skin repair, at least, in part, through the induction of IL-10 expression and dampening of wound inflammation and fibrosis. Therapies that selectively activate VEGFR-2 may therefore be beneficial to treat impaired healing or to prevent excess scarring.

Nanomedicines and gene therapy for the delivery of growth factors to improve perfusion and oxygenation in wound healing

Oxygen plays a key role in wound healing, and hypoxia is a major cause of wound healing impairment; therefore, treatments to improve hemodynamics and increase wound oxygenation are of particular interest for the treatment of chronic wounds. This article describes the roles of oxygen and angiogenesis in wound healing as well as the tools used to evaluate tissue oxygenation and perfusion and then presents a review of nanomedicines and gene therapies designed to improve perfusion and oxygenation and accelerate wound healing.

Tail regeneration and other phenomena of wound healing and tissue restoration in lizards

Wound healing is a fundamental evolutionary adaptation with two possible outcomes: scar formation or reparative regeneration. Scars participate in re-forming the barrier with the external environment and restoring homeostasis to injured tissues, but are well understood to represent dysfunctional replacements. In contrast, reparative regeneration is a tissue-specific program that near-perfectly replicates that which was lost or damaged. Although regeneration is best known from salamanders (including newts and axolotls) and zebrafish, it is unexpectedly widespread among vertebrates. For example, mice and humans can replace their digit tips, while many lizards can spontaneously regenerate almost their entire tail. Whereas the phenomenon of lizard tail regeneration has long been recognized, many details of this process remain poorly understood. All of this is beginning to change. This Review provides a comparative perspective on mechanisms of wound healing and regeneration, with a focus on lizards as an emerging model. Not only are lizards able to regrow cartilage and the spinal cord following tail loss, some species can also regenerate tissues after full-thickness skin wounds to the body, transections of the optic nerve and even lesions to parts of the brain. Current investigations are advancing our understanding of the biological requirements for successful tissue and organ repair, with obvious implications for biomedical sciences and regenerative medicine.

Growth factor pathways in hypertrophic scars: Molecular pathogenesis and therapeutic implications

Hypertrophic scars represent the most common complication of skin injury and are caused by excessive cutaneous wound healing characterized by hypervascularity and pathological deposition of extracellular matrix (ECM) components. To date, the optimal and specific treatment methods for hypertrophic scars have not been available in the clinic. Current paradigm has established fibroblasts and myofibroblasts as pivotal effector cells in the pathophysiology of wound healing. Their biological properties including origin, proliferation, migration, contraction and ECM regulation have profound impacts on the progression and regression of hypertrophic scars. These complex processes are executed and modulated by a signaling network involving a number of growth factors and cytokines. Of particular importance is transforming growth factor-β, platelet-derived growth factor, connective tissue growth factor, epidermal growth factor, and vascular endothelial growth factor. This review article briefly describes the biological functions of fibroblasts and myofibroblasts during hypertrophic scars, and thereafter examines the up-to-date molecular knowledge on the roles of key growth factor pathways in the pathophysiology of hypertrophic scars. Importantly, the therapeutic implications and future challenges of these molecular discoveries are critically discussed in the hope of advancing therapeutic approaches to limit pathological scar formation.

Angiogenesis and wound repair: when enough is enough

All animals heal, and the ability to heal is requisite for human health. One aspect of repair that has always been considered to be essential for adequate healing is the creation of a new vasculature via angiogenesis. As adult skin wounds heal, a period of rapid and robust capillary growth creates a vascular bed that has many fold more capillaries than does normal tissue. Over time, most of the newly formed capillaries regress, resulting in a final vascular density similar to that of normal skin. Certainly, new capillaries are necessary to bring nutrients, immune cells, and oxygen to healing wounds. Yet, the presumed functional importance of an overabundance of capillaries has recently been challenged, creating questions about whether excess capillary growth is truly necessary for healing. In particular, studies of wounds that heal exceptionally quickly and with less scar formation, such as those in fetal skin and oral mucosa, show that these tissues heal with a reduced angiogenic burst composed of more mature vessels that provide better oxygenation. The level of angiogenesis in wounds often correlates with the inflammatory response, largely because inflammatory cells produce an abundance of proangiogenic mediators. Both the selective reduction of inflammation and the selective reduction of angiogenesis have now been suggested as ways to improve scarring. These concepts link excessive inflammation and the production of a dense but poorly perfused capillary bed to inferior healing outcomes.

MicroCT angiography detects vascular formation and regression in skin wound healing

Properly regulated angiogenesis and arteriogenesis are essential for effective wound healing. Tissue injury induces robust new vessel formation and subsequent vessel maturation, which involves vessel regression and remodeling. Although formation of functional vasculature is essential for healing, alterations in vascular structure over the time course of skin wound healing are not well understood. Here, using high-resolution ex vivo X-ray micro-computed tomography (microCT), we describe the vascular network during healing of skin excisional wounds with highly detailed three-dimensional (3D) reconstructed images and associated quantitative analysis. We found that relative vessel volume, surface area and branching number are significantly decreased in wounds from day 7 to days 14 and 21. Segmentation and skeletonization analysis of selected branches from high-resolution images as small as 2.5μm voxel size show that branching orders are decreased in the wound vessels during healing. In histological analysis, we found that the contrast agent fills mainly arterioles, but not small capillaries nor large veins. In summary, high-resolution microCT revealed dynamic alterations of vessel structures during wound healing. This technique may be useful as a key tool in the study of the formation and regression of wound vessels.

Scar-free cutaneous wound healing in the leopard gecko, Eublepharis macularius

Cutaneous wounds heal with two possible outcomes: scarification or near-perfect integumentary restoration. Whereas scar formation has been intensively investigated, less is known about the tissue-level events characterising wounds that spontaneously heal scar-free, particularly in non-foetal amniotes. Here, a spatiotemporal investigation of scar-free cutaneous wound healing following full-thickness excisional biopsies to the tail and body of leopard geckos (Eublepharis macularius) is provided. All injuries healed without scarring. Cutaneous repair involves the development of a cell-rich aggregate within the wound bed, similar to scarring wounds. Unlike scar formation, scar-free healing involves a more rapid closure of the wound epithelium, and a delay in blood vessel development and collagen deposition within the wound bed. It was found that, while granulation tissue of scarring wounds is hypervascular, scar-free wound healing conspicuously does not involve a period of exuberant blood vessel formation. In addition, during scar-free wound healing the newly formed blood vessels are typically perivascular cell-supported. Immunohistochemistry revealed widespread expression of both the pro-angiogenic factor vascular endothelial growth factor A and the anti-angiogenic factor thrombospondin-1 within the healing wound. It was found that scar-free wound healing is an intrinsic property of leopard gecko integument, and involves a modulation of the cutaneous scar repair program. This proportional revascularisation is an important factor in scar-free wound healing.

Pigment epithelium-derived factor as a multifunctional regulator of wound healing

During dermal wound repair, hypoxia-driven proliferation results in dense but highly permeable, disorganized microvascular networks, similar to those in solid tumors. Concurrently, activated dermal fibroblasts generate an angiopermissive, provisional extracellular matrix (ECM). Unlike cancers, wounds naturally resolve via blood vessel regression and ECM maturation, which are essential for reestablishing tissue homeostasis. Mechanisms guiding wound resolution are poorly understood; one candidate regulator is pigment epithelium-derived factor (PEDF), a secreted glycoprotein. PEDF is a potent antiangiogenic in models of pathological angiogenesis and a promising cancer and cardiovascular disease therapeutic, but little is known about its physiological function. To examine the roles of PEDF in physiological wound repair, we used a reproducible model of excisional skin wound healing in BALB/c mice. We show that PEDF is abundant in unwounded and healing skin, is produced primarily by dermal fibroblasts, binds to resident microvascular endothelial cells, and accumulates in dermal ECM and epidermis. PEDF transcript and protein levels were low during the inflammatory and proliferative phases of healing but increased in quantity and colocalization with microvasculature during wound resolution. Local antibody inhibition of endogenous PEDF delayed vessel regression and collagen maturation during the remodeling phase. Treatment of wounds with intradermal injections of exogenous, recombinant PEDF inhibited nascent angiogenesis by repressing endothelial proliferation, promoted vascular integrity and function, and increased collagen maturity. These results demonstrate that PEDF contributes to the resolution of healing wounds by causing regression of immature blood vessels and stimulating maturation of the vascular microenvironment, thus promoting a return to tissue homeostasis after injury.

Anti-Angiogenic Drugs: Involvement in Cutaneous Side Effects and Wound-Healing Complication

Significance: The uses of anti-angiogenic drugs have not only made an impact on the battle to eliminate cancer but are also responsible for a number of medical complications. The long-term use of these drugs has increased the spectrum and incidence of cutaneous side effects and wound-healing complications. It is, therefore, necessary to understand the overall impact that these drugs have on patient care. Recent Advances: This review highlights the role of vascular endothelial growth factor and fibroblast growth factor in angiogenesis and wound healing and looks at how angiogenic inhibitors promote wound-healing complications. Critical Issues: With an increased use of anti-angiogenic drugs for the treatment of various cancers and ocular diseases, there is an increased need for clinicians to define the risks and to optimize the usage of these drugs to reduce the incidence of cutaneous side effects and wound-healing complications. In addition, awareness is needed when treating patients on anti-angiogenic drugs so as not to exacerbate potential wound-healing complications when performing surgical procedures. Future Directions: Clinicians and surgeons will need to develop management guidelines to optimize patient care to reduce the risk of morbidity. When performing a surgical procedure, the impact of adverse effects from the use of anti-angiogenic drugs should be considered to ensure the welfare of the patient. In addition, the development of more specific inhibitors is necessary to reduce target effects to reduce the occurrence of adverse effects.

Vascular Endothelial Growth Factor and Angiogenesis in the Regulation of Cutaneous Wound Repair

Significance: Angiogenesis, the growth of new blood vessels from existing vessels, is an important aspect of the repair process. Restoration of blood flow to damaged tissues provides oxygen and nutrients required to support the growth and function of reparative cells. Vascular endothelial growth factor (VEGF) is one of the most potent proangiogenic growth factors in the skin, and the amount of VEGF present in a wound can significantly impact healing. Recent Advances: The activity of VEGF was once considered to be specific for endothelial cells lining the inside of blood vessels, partly because VEGF receptor (VEGFR) expression was believed to be restricted to endothelial cells. It is now known, however, that VEGFRs can be expressed by a variety of other cell types involved in wound repair. For example, keratinocytes and macrophages, which both carry out important functions during wound healing, express VEGFRs and are capable of responding directly to VEGF. Critical Issues: The mechanisms by which VEGF promotes angiogenesis are well established. Recent studies, however, indicate that VEGF can directly affect the activity of several nonendothelial cell types present in the skin. The implications of these extra-angiogenic effects of VEGF on wound repair are not yet known, but they suggest that this growth factor may play a more complex role during wound healing than previously believed. Future Directions: Despite the large number of studies focusing on VEGF and wound healing, it is clear that the current knowledge of how VEGF contributes to the repair of skin wounds is incomplete. Further research is needed to obtain a more comprehensive understanding of VEGF activities during the wound healing process.

Angiogenesis and scar formation in healing wounds

PURPOSE OF REVIEW

One well described feature of wound healing is the ingrowth of new capillaries or angiogenesis. At its peak, the capillary content in healing wounds may reach three or more times that of normal uninjured tissue. This new vasculature is required to restore oxygenation and allow the growth of new tissue to fill the wound space. This review examines the assumption that a capillary content in excess of normal density is essential for adequate healing.

RECENT FINDINGS

The regulation of wound angiogenesis has been demonstrated to involve both proangiogenic and antiangiogenic stimuli, with the level of capillary growth reliant upon both sets of factors. Several studies now show that normal skin wounds heal adequately even when the angiogenic response is artificially reduced. In normal skin, a reduction of capillary growth to a level consistent with normal tissue does not affect wound closure and may even lead to highly favorable long term healing outcomes.

SUMMARY

The angiogenic response in normal wounds may exceed what is needed for optimal repair.

Mechanisms of vessel regression: toward an understanding of the resolution of angiogenesis

Physiological angiogenesis refers to a naturally occurring process of blood vessel growth and regression, and it occurs as an integral component of tissue repair and regeneration. During wound healing, sprouting and branching results in an extensive yet immature and leaky neovascular network that ultimately resolves by systematic pruning of extraneous vessels to yield a stable, well-perfused vascular network ideally suited to maintain tissue homeostasis. While the molecular mechanisms of blood vessel growth have been explored in numerous cell and animal models in remarkable detail, the endogenous factors that prevent further angiogenesis and control vessel regression have not received much attention and are largely unknown. In this review, we introduce the relevant literature from various disciplines to fill the gaps in the current limited understanding of the major molecular and biomechanical inducers of vascular regression. The processes are described in the context of endothelial cell biology during wound healing: hypoxia-driven activation and sprouting followed by apoptosis or maturation of cells comprising the vasculature. We discuss and integrate the likely roles of a variety of endogenous factors, including oxygen availability, vessel perfusion and shear stress, intracellular negative feedback mechanisms (Spry2, vasohibin), soluble cytokines (CXCL10), matrix-binding proteins (TSP, PEDF), protein cleavage products (angiostatin, vasostatin), matrix-derived anti-angiogenic peptides (endostatin, arresten, canstatin, tumstatin), and the biomechanical properties of remodeling the extra-cellular matrix itself. These factors aid in the spatio-temporal control of blood vessel pruning by inducing specific anti-angiogenic signaling pathways in activated endothelial cells, pathways which compete with pro-angiogenic and maturation signals in the resolving wound. Gaining more insight into these mechanisms is bound to shed light on unresolved questions regarding scar formation, tissue regeneration, and increase our understanding of the many diseases with angiogenic phenotypes, especially cancer.

Fatty acid extracts from Lucilia sericata larvae promote murine cutaneous wound healing by angiogenic activity

BACKGROUND

fatty acids are considered to be effective components to promote wound healing and Lucilia sericata larvae are applied clinically to treat intractable wounds. We aimed to investigate the effect of fatty acid extracts from dried Lucilia sericata larvae on murine cutaneous wound healing as well as angiogenesis.

RESULTS

On day 7 and 10 after murine acute excision wounds creation, the percent wound contraction of fatty acid extracts group was higher than that of vaseline group. On day 3, 7 and 10 after wounds creation, the wound healing quality of fatty acid extracts group was better than that of vaseline group on terms of granulation formation and collagen organization. On day 3 after wounds creation, the micro vessel density and vascular endothelial growth factor expression of fatty acid extracts group were higher than that of vaseline group. Component analysis of the fatty acid extracts by gas chromatography-mass spectrometry showed there were 10 kinds of fatty acids in total and the ratio of saturated fatty acid, monounsaturated fatty acid and polyunsaturated fatty acid (PUFA) was: 20.57%:60.32%:19.11%.

CONCLUSIONS

Fatty acid extracts from dried Lucilia sericata larvae, four fifths of which are unsaturated fatty acids, can promote murine cutaneous wound healing probably resulting from the powerful angiogenic activity of the extracts.

Bone marrow-derived endothelial progenitor cells do not contribute significantly to new vessels during incisional wound healing

OBJECTIVE

To assess the contribution of bone marrow (BM)-derived endothelial progenitor cells (EPCs) to the neovascularisation of cutaneous incisional wounds.

METHODS

Lethally irradiated C57Bl/6 mice were transplanted with BM mononuclear cells from Tie2/lacZ mice, which constitutively overexpressed beta-galactosidase (beta-gal) in endothelial cells (ECs). Chimeras were wounded and the number of X-gal-stained (beta-gal(+)) BM-derived EPCs were calculated in histological wound sections.

RESULTS

EPCs were measured in skin sections from unwounded BM transplant (BMT) mice, or at day 1 and 3 postwounding, at the level of 0.1 +/- 0.1 (mean +/- SEM) per skin/wound section. In day-5 to day-14 wounds, the number of EPCs increased gradually (1.3 +/- 0.5 at day 5 and 4.8 +/- 0.9 at day 10), peaking at day 14, when there was a significant increase in the number of EPCs per wound section (6.5 +/- 1.7) when compared to unwounded skin. Between days 14 and 18 postwounding, there was a rapid fall-off in the number of beta-gal(+) EPCs (0.8 +/- 0.5 at day 18) and numbers returned to baseline by day 21 (0.1 +/- 0.1). No evidence of vascular structures derived from BM-derived EPCs ("in situ" vasculogenesis) was observed and it was calculated that these cells contributed only 4.4% +/- 1.5% to total wound ECs at their peak.

CONCLUSION

These findings indicate that the revascularization of dermal incisional wounds primarily occurs through angiogenesis because the low frequency and temporal expression of EPCs suggests that they do not make a significant contribution to the neovascularization process.