Zebrafish fin regeneration involves transient serotonin synthesis

The zebrafish is a vertebrate organism capable of regenerating many of its organs. Notably, it can undergo epimorphic regeneration of its fins after amputation. This process occurs through the formation of a wound epithelium and the dedifferentiation of mesenchymal and bone‐forming cells, which form a proliferative blastema. Here, we report that the entry into the regenerative process involves the local synthesis of serotonin (5‐hydroxytryptamine, 5‐HT) in the injury‐associated tissue. One day after wounding, intracellular accumulation of serotonin was induced in the stump below the amputation plane. During blastema formation, serotonin was detected in the mesenchyme at the vicinity of the amputation plane and in the apical wound epithelium. During the advanced outgrowth phase, this monoamine was no longer present in the blastema, suggesting a temporal involvement of serotonin in the postinjury area. We show the expression of two serotonin synthesizing enzymes, tryptophan hydroxylase 1a and 1b in the blastema, suggesting the local production of this monoamine. Neither depletion of serotonin by chemical inhibition of tryptophan hydroxylase, nor ectopic administration of this monoamine affected fin regeneration, indicating it does not play a role during this process. Finally, we found that the presence of serotonin during regeneration depends on fibroblast growth factor and retinoic acid signaling. Overall, our study demonstrates that the initiation of fin regeneration is associated with a transient synthesis of serotonin in the regrowing tissue.     

Long‐lasting effects of dexamethasone on immune cells and wound healing in the zebrafish

This study assessed the lasting impact of dexamethasone (DEX) exposure during early development on tissue repair capacity at later life stages (5, 14, and 24 days post fertilization [dpf]) in zebrafish larvae. Using the caudal fin amputation model, we show that prior exposure to DEX significantly delays but does not prevent wound healing at all life stages studied. DEX‐induced impairments on wound healing were fully restored to normal levels with longer post amputation recovery time. Further analyses revealed that DEX mainly exerted its detrimental effects in the early phase (0–5 hours) of wound‐healing process. Specifically, we observed the following events: (1) massive amount of cell death both by necrosis and apoptosis; (2) significant reduction in the number as well as misplacement of macrophages at the wound site; (3) aberrant migration and misplacement of neutrophils and macrophages at the wound site. These events were accompanied by significant (likely compensatory) changes in the expression of genes involved in tissue patterning, including up‐regulation of FKBP5 6 hours post DEX exposure and that of Wnt3a and RARγ at 24 hours post amputation. Taken together, this study provides evidence that DEX exposure during early sensitive periods of development appears to cause permanent alterations in the cellular/molecular immune processes that are involved in the early phase of wound healing in zebrafish. These findings are consistent with previous studies showing that antenatal course of DEX is associated with immediate and lasting alterations of the immune system in rodent models and humans. Therefore, the current findings support the use of the larval zebrafish model to study the impact of stress and stress hormone exposure in immature organisms on health risks in later life.     

The use of a dermal substitute to preserve maximal foot length in diabetic foot wounds with tendon and bone exposure following urgent surgical debridement for acute infection

In this study, we evaluated the utility of a dermal substitute for preserving maximal foot length after urgent surgical debridement. Patients referred to our Diabetic Foot Center with foot lesions were assessed for sensory–motor neuropathy, infection and critical limb ischaemia. The presence of acute foot infection indicated the need for immediate surgical debridement. The degree of amputation, if necessary, was based on the amount of apparently non infected vital tissue. When vital tendon/bone tissue remained exposed, the lesion was covered with a dermal substitute. From January to December 2008, 393 patients underwent surgical treatment for diabetic foot syndrome; 30 patients underwent immediate surgical debridement resulting in exposed tendon and/or bone tissues. An average of 4·4 ± 2·1 days following surgical debridement, all 30 patients underwent dermal regeneration template grafting to cover‐exposed healthy tendon and bone tissues, instead of achieving primary wound closure with a proximal amputation. After 21 days, a skin graft was performed. Complete wound healing occurred in 26 patients (86·7%). In these patients, the amputation level was significantly more distal (P < 0·003) with respect to that potentially required for immediate wound closure. The average healing time was 74·1 ± 28·9 days. Four patients underwent a more proximal amputation. No patients underwent major amputation. The use of the dermal substitute for treating exposed tendon and bone tissues allowed timely wound healing and preserved maximal foot length. Continued follow‐up will allow assessment of long‐term relapse and complication rates. Such treatment could constitute part of the comprehensive management of diabetic wounds.     

Level‐specific amputations and resulting regenerative outcomes in the mouse distal phalanx

Mouse digit tip regeneration involves an intricate coordinated regrowth of the terminal phalanx, nail, dermis and epidermis. During this time, regenerating digits undergo wound healing, blastema formation, and differentiation. However, the regenerative response of the digit is dependent on the level of the amputation. Amputation of <30% of the distal phalanx (P3), with part of the base nail remaining, results in extensive digit regeneration. In contrast, >60% P3 removal results in no regeneration. This level‐dependent regenerative ability of the mouse digit provides a comparative model between regeneration and non‐regeneration that may enable identification of specific factors critical to regeneration. Although the ability to create regenerating and non‐regenerating conditions has been well established, the regenerative response between these regions (“intermediate” zone) has received less scrutiny, and may add insight to the regenerative processes, including the degree of histolysis, and the level of blastema formation. The objective of this study is then to compare the regeneration capacity between amputation levels within the regenerating (<30%), intermediate (40–59%), and non‐regenerating (>60%) regions. Results indicated that regenerative and intermediate amputations led to significant histolysis and blastema formation of the distal phalanx 14 days post‐amputation. Unlike the regenerating digits, intermediate amputations led to incomplete regeneration whereby regrowth of the digits were not to the levels of the intact or regenerating digits. Non‐regenerating amputations did not exhibit significant histolysis or blastema formation. Remarkably, the histolytic process resulted in day 14 P3 lengths that were similar regardless of the initial amputation over 19%. The differences in histolysis, blastema formation and injury outcomes were also marked by changes in the number of proliferating cells and osteoclasts. Altogether, these results indicate that although intermediate amputations result in histolysis and blastema formation similar to regenerating digits, the resulting cellular composition of the blastema differs, contributing to incomplete regeneration.     

Does closed incision negative wound pressure therapy in non‐traumatic major lower‐extremity amputations improve survival rates?

Closed incision negative pressure wound therapy (CINPWT) has been shown to be clinically effective compared with the traditional gauze dressing, reducing surgical site infections and wound complications. We evaluated the effect of CINPWT compared with gauze dressing on the need for revision surgery and survival after non‐traumatic major lower amputation. We included 309 patients undergoing 403 major lower amputations in a retrospective study from January 1, 2010 to November 23, 2017. A total of 139 patients received CINPWT, and 170 patients received stump bandage. There was no statistically significant difference between the two groups regarding the need for revision surgery (P = .45). Fourteen stump bandage patients and 15 CINPWT patients died in hospital (P = .57). One year after amputation, 55 CINPWT patients and 66 stump bandage patients had died (P = .82). Survival probabilities adjusted for age and gender 2 years after amputation were .52 (.43‐.61) and .49 (.42‐.58), respectively, and 3 years after amputation were .36 (.25‐.50) and .39 (.32‐.47), respectively. We also found no significant difference in the need for revision surgery in survival probabilities up till 3 years after amputation between patients treated with CINPWT and patients treated with gauze bandage postoperatively.     

Tissue restoration: approaches and prospects

This article summarizes the results of three basic research approaches directed toward achieving the restoration of injured or diseased human tissues. The three approaches are (1) to understand the differences in the molecular characteristics of cells and their environments in tissues which exhibit regenerative capacity at one stage of the life cycle but not at another; (2) to understand the molecular mechanisms whereby tissues regenerate by means of reserve progenitor cells or progenitor cells formed by dedifferentiation; and (3) to design artificial tissues for implantation into the body. These strategies should allow us to locate the key switchpoints which determine regeneration versus repair and how to reconfigure those switchpoints into a regenerative circuit where necessary or to build tissues in vitro that can serve as in vivo substitutes. For these strategies to be successful, we must understand the role of the immune system in repair and regeneration and the developmental roles of regulatory molecules, such as growth factors, trophic factors, extracellular matrix components, and the protein products of patterning genes, as well as the intracellular signaling systems activated by these molecules. The examples used to illustrate these themes are repair versus regeneration in wounded mammalian skin, the regeneration of injured mammalian bone and muscle by reserve progenitor cells, and the regeneration of the urodele limb, neural retina, and lens by progenitor cells produced by dedifferentiation. In addition, several approaches used in the construction of bioartificial tissues are discussed.     

Efficacy and cost‐effectiveness of octenidine wound gel in the treatment of chronic venous leg ulcers in comparison to modern wound dressings

The aim of this study was to determine the efficacy, safety and cost‐effectiveness of an octenidine‐based wound gel in the treatment of chronic venous leg ulcers. For this purpose, 49 wounds were treated with either modern wound‐phase‐adapted dressings alone (treatment arm 1; n = 17), octenidine wound gel plus modern wound‐phase‐adapted dressings (treatment arm 2; n = 17) or octenidine wound gel alone (treatment arm 3; n = 15). During the study period of 42 days with dressing changes every 3–5 days, wound healing characteristics and treatment costs of different dressings were analysed. Wound size reduction was significantly better (P = 0·028) in both octenidine wound gel treatment arms compared to modern dressings alone with total reductions of 14·6%, 64·1% and 96·2% in treatment arms 1–3. Early wound healing was merely observed under octenidine wound gel treatment (n = 9), whereby lowest treatment costs were generated by octenidine wound gel alone (€20·34/dressing change). As a result, the octenidine wound gel is cost‐effective and well suitable for the treatment of chronic venous leg ulcers, considering both safety and promotion of wound healing.     

Chylothorax following traumatic amputation of upper arm

A young patient who had traumatic amputation of left arm developed extensive chylothorax on right side of chest. The pathophysiology appears to be left subclavian thrombosis secondary to gross sepsis of the amputation stump which resulted in occlusion of thoracic duct opening and chylothorax. The child was successfully treated by closed chest tube drainage.     

Progress of cellular dedifferentiation research

Differentiation, the stepwise specialization of cells, and transdifferentiation, the apparent switching of one cell type into another, capture much of the stem cell spotlight. But dedifferentiation, the developmental reversal of a cell before it reinvents itself, is an important process too. In multicellular organisms, cellular dedifferentiation is the major process underlying totipotency, regeneration and formation of new stem cell lineages. In humans, dedifferentiation is often associated with carcinogenesis. The study of cellular dedifferentiation in animals, particularly early events related to cell fate-switch and determination, is limited by the lack of a suitable, convenient experimental system. The classic example of dedifferentiation is limb and tail regeneration in urodele amphibians, such as salamanders. Recently, several investigators have shown that certain mammalian cell types can be induced to dedifferentiate to progenitor cells when stimulated with the appropriate signals or materials. These discoveries open the possibility that researchers might enhance the endogenous regenerative capacity of mammals by inducing cellular dedifferentiation in vivo.     

Endotoxin testing of a wound debridement device containing medicinal Lucilia sericata larvae

Alimentary products of medicinal Lucilia sericata larvae are studied to determine their mechanisms of action, particularly in the contexts of wound debridement and disinfection. Furthermore, the larvae can be applied to patients in contained medical devices (such as the BioBag; BioMonde). Here, we tested the materials and larval content of the most commonly used debridement device (the “BB‐50”) to explore the possibility that endotoxins may be contributing to the bio‐activity of the product, given that endotoxins are potent stimulants of cellular activation. Using standardised protocols to collect larval alimentary products (LAP), we proceeded to determine residual endotoxin levels in LAP derived from the device, before and after the neutralisation of interfering enzymatic activity. The debridement device and its associated larval content was not a significant source of lipopolysaccharide (LPS) activity. However, it is clear from these experiments that a failure to remove the confounding serine proteinase activity would have resulted in spuriously high and erroneous results. The residual LPS levels detected are unlikely to be active in wound healing assays, following cross‐referencing to publications where LPS at much higher levels has been shown to have positive and negative effects on processes associated with wound repair and tissue regeneration.     

Inflammatory biomarkers,vascular procedures of lower limbs,and wound healing

Abnormal, persistent inflammation after bypass surgery could prevent healing of an ischaemic foot lesion. In 37 patients with peripheral arterial disease (PAD) (Rutherford Grade III Category 5) who underwent infrapopliteal vein graft and midfoot amputation, plasma levels of fibrinogen, C‐reactive protein (CRP), interleukin‐1 (IL‐1), interleukin‐6 (IL‐6), tumour necrosis factor‐α (TNF‐α), and matrix metalloproteinase‐2 and ‐9 (MMP‐2 and MMP‐9) were determined preoperatively and during the follow up. Nine patients without clinical and Doppler evidence of arterial disease, who underwent post‐traumatic midfoot primary amputation, were included in the experiment group, and 15 age‐matched healthy volunteers served as control. In patients who had midfoot amputation for trauma, all wounds healed. Seven (19%) wounds in patients with an occluded graft healed, and five (13%) required major amputation because of a non‐healing wound. Time required for complete healing of the lesion was similar between trauma and PAD patients (8 ± 2 months vs 11 ± 6, respectively, P = NS). Univariate analysis demonstrated that, in PAD patients, the postoperative high levels of TNF‐α, IL‐6, and MMP‐2 and ‐9 were predictive for wound healing failure at 3, 6, and 9 months (P < 0.05), respectively. Furthermore, the subgroup of patients who experienced occlusion of the vein graft during follow up had a significant increase of MMP‐2, ‐9, IL‐6, and TNF‐α at 3, 6, and 9 months (P < 0.05), respectively. Monitoring inflammatory markers allows the determination of patients at risk of healing failure of midfoot amputation after distal revascularisation and might predict the fate of the vein graft.     

Maggot therapy for wound debridement in a traumatic foot-degloving injury: a case report

A 43-year-old man was treated for a traumatic degloving injury to his foot with a transmetatarsal amputation and wound care because of the extensive soft tissue loss. After biweekly sharp debridements in the office for 4 weeks, very minimal skin ingrowth was noted. Maggot therapy was then implemented for a 48-hour treatment and a second treatment for 72 hours to help reduce excessive fibrosis and to painlessly debride the tissues to expose the granular base. Daily dressing changes for the next 6 weeks successfully allowed complete wound closure without any additional interventions. During the follow-up course, no complications were encountered and the patient has returned to ambulation with the use of a cane.     

From scarless fetal wounds to keloids: Molecular studies in wound healing

Surgical researchers were among the first to describe the different phases of wound healing and the events in tissue repair and regeneration that were taking place during each phase. The understanding of these events has been significantly enhanced in recent years by modern techniques in molecular and cellular biology. In this article, we discuss new findings in scarless fetal repair, angiogenesis in wound healing, and keloid pathogenesis. This serves to highlight the advances that have been made and also how much remains to be understood.     

Causes and consequences of epigenetic regulation in wound healing

Wound healing is a complex and systematic tissue level response to mechanical and chemical injuries that may cause the release of growth factors, cytokines, and chemokines by damaged tissues. For the complex features of these restorative processes, it is a crucial challenge to identify the relevant cell types and biochemical pathways that are involved in wound healing. Epigenetic mechanisms, such as DNA methylation, histone modification, and noncoding regulatory RNA editing, play important roles in many biological processes, including cell proliferation, migration and differentiation, signal pathway activation or inhibition, and cell senescence. Epigenetic regulations can coordinately control a considerable subset of known repair genes and thus serve as master regulators of wound healing. An abundance of evidence has also shown that epigenetic modifications participate in the short‐ and long‐term control of crucial gene expression and cell signal transduction that are involved in the healing process. These data provide a foundation for probable epigenetic‐based therapeutic strategies that are aimed at stimulating tissue regeneration. This review describes the epigenetic alterations in different cellular types at injury sites, induced signals, and resulting tissue repair. With the increased interest in the epigenetics of wound and repair processes, this field will soon begin to flourish.     

Apoptosis in regenerating and denervated, nonregenerating urodele forelimbs

Denervated limbs of larval salamanders fail to regenerate if amputated and, unlike adult limbs, undergo regression. The cellular basis of the tissue loss is poorly understood. We used TUNEL staining of larval axolotl limbs fixed and sectioned at intervals after bilateral amputation and unilateral denervation to investigate the role of apoptosis during normal limb regeneration and denervated limb regression. In the first week after amputation a small percentage of apoptotic cells was found in both innervated and denervated limbs. During the second week the apoptotic index remained low in the mitotically active mesenchymal cells of the regenerating limbs, but increased twofold in the nondividing, dedifferentiated cells of the regressing limbs. TUNEL-positive cells resembling apoptotic bodies were restricted primarily to the dedifferentiated area beneath the wound epithelium, but were also present within the wound epithelium itself. Macrophages were identified immunohistochemically and were also found in increased numbers in distal areas of the denervated regressing limbs. The results suggest a role for apoptosis in the early phase of normal regeneration and indicate that denervated limb regression involves an increased rate of apoptosis and removal of apoptotic bodies by macrophages and the wound epithelium.     

Immunomodulator ‘mushroom beta glucan’ induces Wnt/β catenin signalling and improves wound recovery in tilapia and rat skin: a histopathological study

The present study aims to investigate the effects of mushroom beta glucan (MBG) on wound recovery in partial hepatectomy (PH) in Nile tilapia (Oreochromis niloticus) and in rat skin wound healing examination. Following PH, we focussed on the effects on liver repair ability using in vitro and in vivo tests. In vitro, we examined whether the MBG has an impact on liver cell proliferation, mainly through 3‐(4,5‐dimethylthiazolyl‐2)‐2,5‐diphenyltetrazolium bromide (MTT) assays and bromodeoxyuridine (BrdU) cell proliferation assay detection method. Results showed that MBG treatment was remarkable in enhancing cell proliferation of hepatocytes and in maintaining the cellular viability. Immunohistochemical staining to analyse Wnt/β‐catenin signalling also showed that MBG has the effect of promoting cell proliferation of liver tissues after PH surgery.     

Fetal wound healing: an overview

The ability of fetal tissues to heal without scarring has prompted extensive research into the biochemical and molecular differences between fetal and postnatal wound healing. A thorough understanding of the basic mechanisms of fetal wound repair may to lead to approaches to correct or prevent the clinical problems encountered in abnormal adult wound healing and fetal surgery. This article contrasts the normal healing response in adults with fetal repair in animal models, highlighting investigations of extracellular matrix expression, cytokine profiles, and cellular dynamics.     

Proximal digit tip amputation initiates simultaneous blastema and transient fibrosis formation and results in partial regeneration

Complete extremity regeneration in mammals is restricted to distal amputations of the digit tip, the terminal phalanx (P3). In mice, P3 regeneration is mediated via the formation of a blastema, a transient population of progenitor cells that form from the blending of periosteal and endosteal/marrow compartmentalized cells that undergo differentiation to restore the amputated structures. Compartmentalized blastema cells are formed independently, and periosteal compartment‐derived cells are required for restoration of amputated skeletal length. P3 regenerative capacity is progressively attenuated at increasingly more proximal amputation levels, eventually resulting in regenerative failure. The continuum of regenerative capacity within the P3 wound milieu is a unique model to investigate mammalian blastema formation in response to distal amputation, as well as the healing response associated with regenerative failure at proximal amputation levels. We report that P3 proximal amputation healing, previously reported to result in regenerative failure, is not an example of complete regenerative failure, but instead is characterized by a limited bone regeneration response restricted to the endosteal/marrow compartment. The regeneration response is mediated by blastema formation within the endosteal/marrow compartment, and blastemal osteogenesis progresses through intramembranous ossification in a polarized proximal to distal sequence. Unlike bone regeneration following distal P3 amputation, osteogenesis within the periosteal compartment is not observed in response to proximal P3 amputation. We provide evidence that proximal P3 amputation initiates the formation of fibrotic tissue that isolates the endosteal/marrow compartment from the periosteal compartment and wound epidermis. While the fibrotic response is transient and later resolved, these studies demonstrate that blastema formation and fibrosis can occur in close proximity, with the regenerative response dominating the final outcome. Moreover, the results suggest that the attenuated proximal P3 regeneration response is associated with the absence of periosteal‐compartment participation in blastema formation and bone regeneration.