Regional disturbances in blood flow and metabolism in equine limb wound healing with formation of exuberant granulation tissue

L. The effects of a synthetic epidermis spray on secondary intention wound healing in adult horses

OBJECTIVES

To evaluate secondary intention wound healing in the horse's limbs when treated with the synthetic epidermis spray (Novacika®, Cohesive S.A.S, France) or with a standard bandaging technique.

METHODS

Six Standardbred mares were included in the study. Four 2.5 x 2.5 cm full-thickness skin wounds were created on each thoracic limb. Two wounds were located on the dorsoproximal aspect of the cannon bone and the other two at the dorsoproximal aspect of the fetlock. Six hours after creation, wounds were randomly treated with synthetic epidermis spray or standard bandaging. The wounds were assessed every 4 days by gross visual assessment and using a 3D imaging camera. Analysis was performed with a 3D imaging application.

RESULTS

Out of 46 wounds, 22 showed exuberant granulation tissue and were part of the standard bandaging group. Whether the wounds were treated with synthetic epidermis spray or standard bandaging, the time for healing was the same.

CONCLUSION

The synthetic epidermis spray studied in this model has allowed healing without the production of exuberant granulation tissue but did not reduce the median wound healing time compared to a standard bandaging technique. The synthetic epidermis spray is potentially an interesting alternative for the management of secondary intention wound healing of superficial and non-infected distal limb wounds in adult horses on economical and practical aspects. However, all statistical inference (p-values especially) must be interpreted with caution, given the size of the sample.

The granulation (t)issue: A narrative and scoping review of basic and clinical research of the equine distal limb exuberant wound healing disorder

Exuberant granulation tissue (EGT) is often observed during second intention wound healing in horses. Despite its impact on wound care, the basic mechanisms leading to EGT are still unclear and effective strategies to prevent and/or treat EGT are lacking. The development of EGT is a poorly understood, multifactorial process involving hyperproliferating fibroblasts and malfunctional differentiation of keratinocytes, suboptimal wound contraction, dysfunctional vascularisation, and chronic inflammation. To consolidate and describe basic and clinical research literature on EGT and to identify knowledge gaps and opportunities for future research, a search was systematically conducted using predefined search terms. Subsequently, a scoping review was conducted using specific criteria to select the peer-reviewed literature that described methods to treat and/or prevent EGT. Proposed mechanisms of effects as well as results and main conclusions were extracted and tabulated. The systematic search resulted in 1062 publications in PubMed and 767 in Web of Science. Twenty additional studies were later included. Of these, 327 studies were reviewed for the narrative review on basic research and 35 controlled clinical trials were eligible for the scoping review. All 35 studies were conducted in university hospitals, and all but one involved surgically induced non-infected wounds. The study population was predominantly horses (n = 230) with a small number of ponies (n = 18) and donkeys (n = 14). In conclusion, there remains a strong need for evidence-based recommendations on EGT treatment, preferably using multi-centre studies that represent the general population of horses, include higher numbers of animals, and are performed in naturally occurring wounds. This narrative and scoping review also emphasises the importance of incorporating basic research knowledge in the study design of clinical trials.

Biofilm and Equine Limb Wounds

In chronic wounds in humans, biofilm formation and wound chronicity are linked, as biofilms contribute to chronic inflammation and delayed healing. Biofilms are aggregates of bacteria, and living as biofilms is the default mode of bacterial life; within these aggregates, the bacteria are protected from both antimicrobial substances and the immune response of the host. In horses, delayed healing is more commonly seen in limb wounds than body wounds. Chronic inflammation and hypoxia are the main characteristics of delayed wound healing in equine limbs, and biofilms might also contribute to this healing pattern in horses. However, biofilm formation in equine wounds has been studied to a very limited degree. Biofilms have been detected in equine traumatic wounds, and recent experimental models have shown that biofilms protract the healing of equine limb wounds. Detection of biofilms within wounds necessitates advanced techniques that are not available in routine diagnostic yet. However, infections with biofilm should be suspected in equine limb wounds not healing as expected, as they are in human wounds. Treatment should be based on repeated debridement and application of topical antimicrobial therapy.

Transcriptional adaptation of Mycobacterium ulcerans in an original mouse model: New insights into the regulation of mycolactone

Mycobacterium ulcerans is the causal agent of Buruli ulcer, a chronic infectious disease and the third most common mycobacterial disease worldwide. Without early treatment, M. ulcerans provokes massive skin ulcers, caused by the mycolactone toxin, its main virulence factor. However, spontaneous healing may occur in Buruli ulcer patients several months or years after the disease onset. We have shown, in an original mouse model, that bacterial load remains high and viable in spontaneously healed tissues, with a switch of M. ulcerans to low levels of mycolactone production, adapting its strategy to survive in such a hostile environment. This original model offers the possibility to investigate the regulation of mycolactone production, by using an RNA-seq strategy to study bacterial adaptation during mouse infection. Pathway analysis and characterization of the tissue environment showed that the bacillus adapted to its new environment by modifying its metabolic activity and switching nutrient sources. Thus, M. ulcerans ensures its survival in healing tissues by reducing its secondary metabolism, leading to an inhibition of mycolactone synthesis. These findings shed new light on mycolactone regulation and pave the way for new therapeutic strategies.

A Critical Overview of the Use of Platelet-Rich Plasma in Equine Medicine Over the Last Decade

In the 1990s, the role of platelets in inflammation and tissue healing was finally recognized. Since then, the clinical use of platelet-derived products (hemocomponents), such as, platelet-rich plasma (PRP), markedly increased. The promise of a more economical option of a disease-modifying treatment led to the intensive and continuous research of PRP products and to its widespread clinical use. A number of protocols and commercial kits have been developed with the intention of creating a more practical and reliable option for clinical use in equine patients. Still, the direct comparison between studies is particularly challenging due to the lack of standardization on the preparation methods and product composition. The incomplete reports on PRP cellular concentration and the poorly designed in vivo studies are additional matters that contest the clinical efficiency of this biomaterial. To overcome such challenges, several in vitro and in vivo studies have been proposed. Specifically, experiments have greatly focused in protocol optimization and its effect in different tissues. Additionally, in vivo studies have proposed different biological products envisioning the upgrade of the anti-inflammatory cytokines trusting to increase its anti-inflammatory effect. The individual variability and health status of the animal, type of tissue and condition treated, and protocol implemented are known to influence on the product's cell and cytokine composition. Such variability is a main clinical concern once it can potentially influence on PRP's therapeutic effects. Thus, lack of qualitative and quantitative evidence-based data supporting PRP's clinical use persists, despite of the numerous studies intended to accomplish this purpose. This narrative review aims to critically evaluate the main research published in the past decade and how it can potentially impact the clinical use of PRP.

The evaluation of the effect of probiotics on the healing of equine distal limb wounds

The effect of dressings saturated with either a standardized suspension of probiotic bacteria or saline on healing of traumatic distal limb wounds in horses was evaluated for 24 days, and the systemic inflammatory effect was assessed. The wounds were divided in two groups based on the phase of healing: wounds with an incomplete (ICGB) or a complete granulation bed (CGB). The wound area was expressed as percentage of the wound area at day 0 and defined as relative wound area. The mean relative wound area decreased faster in probiotic than saline treated wounds. The difference was most obvious in CGB and increased rapidly from day 0 until day 12 up to 30%, and stabilized around 25% thereafter until the end of the observation period, but it was not statistically significant because of the large variation within the treatment groups. The mean wound area of CGB decreased to 28.4% (range: 6.3 to 49.3) with probiotic and to 51.9% (range: 29.3 to 81.7) with saline treatment at day 24. Additionally, the rate to 50% healing in CGB was 3.4 faster with probiotic compared to saline treatment, whereas in ICGB this was 1.9 faster. Topical probiotics did not increase serum amyloid A and white blood cell counts. Although the mentioned differences were not statistically significant, the clinical relevance of the effect of treatment with probiotics in CGB wounds is clear, supported by the differences in mean wound area in course of time and the time required to reach 50% healing (day 12 for probiotic vs more than day 24 for saline treated wounds). Thus the probiotic treated wounds reached 50% reduction in wound area in half of the time of the saline treated wounds. The topical use of probiotics can be considered as safe as it did not cause a systemic effect.

Histologic changes and gene expression patterns in biopsy specimens from bacteria-inoculated and noninoculated excisional body and limb wounds in horses healing by second intention

OBJECTIVE

To evaluate histologic changes and gene expression patterns in body and limb wounds in horses in response to bacterial inoculation.

SAMPLE

Wound biopsy specimens from 6 horses collected on days 7, 14, 21, and 27 after excisional wounds (20 wounds/horse) were created over the metacarpal and metatarsal region and lateral thoracic region (body) and then inoculated or not inoculated on day 4 with Staphylococcus aureus and Pseudomonas aeruginosa.

PROCEDURES

Specimens were histologically scored for the amount of inflammation, edema, angiogenesis, fibrosis organization, and epithelialization. Quantitative PCR assays were performed to quantify gene expression of 10 inflammatory, proteolytic, fibrotic, and hypoxia-related markers involved in wound healing.

RESULTS

Except for gene expression of interleukin-6 on day 27 and tumor necrosis factor-α on day 14, bacterial inoculation had no significant effect on histologic scores and gene expression. Gene expression of interleukin-1β and -6, serum amyloid A, and matrix metalloproteinase-9 was higher in limb wounds versus body wounds by day 27. Gene expression of cellular communication network factor 1 was higher in limb wounds versus body wounds throughout the observation period.

CONCLUSIONS AND CLINICAL RELEVANCE

The lack of clear markers of wound infection in this study reflected well-known difficulties in detecting wound infections in horses. Changes consistent with protracted inflammation were evident in limb wounds, and gene expression patterns of limb wounds shared similarities with those of chronic wounds in humans. Cellular communication network factor warrants further investigation and may be useful in elucidating the mechanisms underlying poor limb wound healing in horses.

An Equine Wound Model to Study Effects of Bacterial Aggregates on Wound Healing

Objective: Relevant animal models to study effects of bacterial aggregates on wound healing are lacking. We aimed at establishing an equine wound model with bacterial aggregates to investigate the impact of bacterial inoculation on normal (thorax) and impaired (limb) wound healing. Approach: Wounds were created on three limbs and both thorax sides of six horses. Twelve out of 20 wounds per horse were inoculated with 10⁴ Staphylococcus aureus and 10⁵ Pseudomonas aeruginosa on day 4. Healing was monitored until day 27 by clinical assessment, including wound scoring, surface pH measurements, and digital photography for area determination. Biopsies were used for bacterial culture and for peptide nucleic acid fluorescence in situ hybridization to detect bacterial aggregates. Results: Inoculated limb wounds healed slower than noninoculated limb wounds from day 10 onward (p < 0.0001). Inoculated and noninoculated thorax wounds healed equally well and faster than limb wounds. The odds ratio of detecting bacterial aggregates in inoculated limb wounds was 7.1 (2.4-21.0, p = 0.0086) compared with noninoculated limb wounds and 36.2 (3.8-348, p = 0.0018) compared with thorax wounds. Innovation: This equine wound model with bacterial aggregates might be superior to other animal wound models, as both normal and impaired healing can be studied simultaneously. In this model, many aspects of wound healing, including novel treatments, may be studied. Conclusions: The impaired healing observed in inoculated limb wounds may be related to the persistent bacterial aggregates. Both in capability of clearing inoculated bacteria from the wounds and in healing pattern, thorax wounds were superior to limb wounds.

Thermographic evaluation of primary closure and second intention healing in dairy calves

OBJECTIVE

To evaluate the suitability of infrared thermography in assessing healing of surgically created wounds that are managed by primary closure or second intention in neonatal dairy calves during a 3-week period.

STUDY DESIGN

Randomized clinical trial.

ANIMALS

Six Jersey bull calves.

METHODS

Two skin patches approximately 10 cm² were shaved on each hind limb of all calves. The dorsal patch was designated the wound creation site, and the ventral patch was the control. The wound creation sites were randomly assigned for either primary closure or healing by second intention. Wounds were created by using an 8-mm biopsy punch. Thermographic imaging was performed prior to wound creation and at 0 minutes; 15 minutes; 2, 4, 8, 12, and 24 hours; and 2, 3, 4, 7, 10, 14, and 21 days postwounding.

RESULTS

There were no differences in skin temperature changes observed between wounds that were managed by primary closure or second intention (P = .9934) at any time. Time after wound creation had an effect on the skin temperature (P < .0001), with skin temperature consistently warmer (P < .05) 2, 4, and 8 hours after creation of wounds compared with subsequent times.

CONCLUSION

Infrared thermography was unable to detect differences in wound healing by primary closure or second intention in this model.

CLINICAL SIGNIFICANCE

Thermographic monitoring to detect differences in wound healing was not evident in this model. This model might be useful in monitoring temporal changes during early wound repair.

Growth and function of equine endothelial colony forming cells labeled with semiconductor quantum dots

BACKGROUND

Endothelial progenitor cells (EPCs) contribute to neovascularization and vascular repair in vivo and are attractive for clinical use in ischemic disease. Tracking of stem and progenitor cells is essential to determine engraftment after administration. Semiconductor quantum dots (QD) are promising for cell labeling due to their ease of uptake by many cell lines and their continued presence after many cell generations. The purpose of this study was to evaluate function and growth of equine EPCs after QD labeling. Additionally, this study evaluated the duration of QD label retention and mechanisms of QD label loss.

RESULTS

Endothelial colony forming cells (ECFCs) from adult horses (N = 3) were employed for this study, with QD labeled and unlabeled ECFCs tested from each horse. Cell proliferation of ECFCs labeled with QD at 20 nM was quantified by comparing the number of cell doublings per day (NCD) and the population doubling time (PDT) in labeled and unlabeled cells. Function of labeled and unlabeled ECFCs was assessed by comparing uptake of acetylated low-density lipoprotein (DiO-Ac-LDL) and tubule formation on growth factor containing matrix. Cell proliferation was not impacted by QD labeling; both NCD (p = 0. 95) and PDT (P = 0. 91) did not differ between unlabeled and QD labeled cells. Function of ECFCs assessed by DiO-Ac-LDL and tubule formation was also not different between unlabeled and QD labeled cells (P = 0. 33 and P = 0. 52, respectively). ECFCs retained their QD labeling over 7 passages with both 5 nM and 20 nM label concentrations. Reduction in label intensity was observed over time, and the mechanism was determined to be cell division.

CONCLUSIONS

Equine ECFCs are effectively labeled with QD, and QD concentrations up to 20 nM do not affect cell growth or function. QD label loss is a result of cell division. The use of QD labeling with equine EPCs may be an ideal way to track engraftment of EPCs for in vivo applications.

Evaluation of Systemic and Local Inflammatory Parameters and Manifestations of Pain in an Equine Experimental Wound Model

In the last decades, a well-established equine wound model has been used to study fibroproliferative wound healing disorders. The aim of this study was to characterize the degree of discomfort of wounding and sampling in an equine excisional wound model by evaluating systemic and local inflammatory responses and signs of pain. A total of 12 cutaneous wounds, three on each shoulder and each metatarsus, were created in a standing surgical procedure. Wounds were biopsied on days 2, 4, 7, 14, 21, and 28 after surgery. Clinical parameters (rectal temperature, heart rate, respiratory frequency) and blood levels of white blood cell, serum amyloid A, fibrinogen, and iron were monitored to evaluate the systemic inflammatory response. Local signs of inflammation (swelling, heat, pain) were subjectively assessed, the limb circumference recorded, and temperature of the wound measured by thermometry. Pain was evaluated by a composite measure pain scale (CMPS). The results demonstrated that the wounding procedure elicits an inflammatory response. Day 1 after surgery, two horses scored 2 and 7 units (of 27 units), respectively, on the CMPS, and day 8 after surgery, one horse scored 3 units. The biopsy procedure did not elicit local or systemic signs of inflammation. Based on these findings, it appears that the equine experimental wound model causes mild discomfort and pain manifestations. This information is important for researchers, who consider using the model. To justify the use of an animal model, it should be demonstrated that the expected benefits of the research outweigh the discomfort imposed to the animal.

Treatment of limb wounds of horses with orf virus IL-10 and VEGF-E accelerates resolution of exuberant granulation tissue, but does not prevent its development

Bandaging of limb wounds in horses leads to formation of exuberant granulation tissue (EGT) that retards healing due to protracted inflammation, aberrant vascularisation and delayed epithelialisation. EGT is not observed if wounds are left undressed or when wounds are on the body. A previous study showed that short-term administration of proteins derived from orf virus dampened inflammation and promoted epithelialisation of open wounds in horses. Here, we investigated the impact of orf virus interleukin-10 and vascular endothelial growth factor-E on the development and resolution of EGT. Excisional wounds were created on the forelimb of four horses, and bandages were maintained until full healing to induce EGT formation. Matching body wounds were created to ensure EGT was limited to the limb, and to differentiate the effects of the viral proteins on normal healing and on EGT formation. Viral proteins or the hydrogel vehicle control were administered topically to site-matched wounds at day 1, with repeat administration at day 8. Wound healing and EGT formation were monitored macroscopically. Wound margin samples were harvested at 2, 7 and 14 days, and at full healing, with histology used to observe epithelialisation, immunofluorescence used to detect inflammatory cells, angiogenesis and cell death, and qPCR to measure expression of genes regulating inflammation and angiogenesis. Limb wounds developed EGT, and exhibited slower healing than body wounds. Viral protein treatment did not accelerate healing at either location nor limit EGT formation in limb wounds. Treatment of limb wounds did however increase epithelialisation and angiogenesis, without dampening inflammatory cell infiltration or gene expression. The healed wounds also had less occlusion and death of blood vessels and fewer epidermal rete ridges following viral protein treatment. These findings indicate that the viral protein treatment does not suppress wound inflammation or EGT formation, but does promote vascular and epidermal repair and EGT resolution.

Normal microscopic anatomy of equine body and limb skin: A morphological and immunohistochemical study

INTRODUCTION

Information on microscopic anatomy of equine skin is sparse. In horses, limb wounds often become chronic and/or non-healing whereas body wounds heal normally. These dissimilarities in healing patterns might be a product of different phenotypic characteristics of body and limb skin. The objective of this study was to investigate microscopic anatomy, epidermal thickness, keratinocyte proliferation and differentiation as well as the presence of mast cells in normal equine skin of body and limb.

MATERIALS AND METHODS

The study involved body and limb skin biopsies from six horses. Histological characteristics of the epidermis were assessed and epithelial thickness measured. Immunohistochemistry was performed to investigate epidermal differentiation patterns of cytokeratin (CK) 10, CK14, CK16, loricrin, and peroxisome proliferator-activated receptor alpha (PPAR-α), epidermal proliferation (Ki-67 immunostaining), and mast cells distribution in the skin.

RESULTS

The epidermis was significantly thicker in the limb skin compared to body skin (p<0.01). Epidermal proliferation and CK distribution did not show differences in the two anatomical areas. Loricrin presence was focally found in the spinous layer in four out of six limb skin samples but not in body skin samples. Tryptase positive mast cells were detected in the dermis and their density (cell/mm²) was not different between body and limb.

DISCUSSION AND CONCLUSION

Here we report for the first time about the normal distribution of CK10, CK14, CK16, PPAR-α, and loricrin in equine limb and body skin as well as about epidermal proliferation rate and mast cell count. It will be relevant to investigate the distribution of the investigated epithelial differentiation markers and the role of mast cells during equine wound healing and/or other skin diseases.

Platelet-rich plasma to treat experimentally-induced skin wounds in animals: A systematic review and meta-analysis

The objective of the study was to review current literature to determine whether the topical application of platelet-rich plasma (PRP) promotes healing in experimentally-induced full-thickness skin wounds in animals. The hypothesis was that the adjunct of PRP has a positive effect on wound healing. An electronic search was carried out on the following databases: Web of Science, Cochrane Library, PubMed, Research Gate, Cochrane Wounds Group, Veterinary Information Network. No publication date nor language restrictions were applied. Randomised and not randomised controlled clinical trials comparing PRP with placebo or with other treatments were included. The reduction of open wound area in PRP-treated (test) wounds compared to control wounds was the primary outcome. Secondary outcomes were healing time and number of healed cases in test group compared to control. The following effect sizes were calculated: the Hedges' g for continuous variables; the odds ratio for binary data. Eighteen controlled clinical trials were included in the qualitative and quantitative synthesis, with a total of 661 wounds. All studies were published in the period 2007-2016. Eight studies were carried out on rodent/lagomorph mammals and 10 on non-rodent/lagomorph mammals. In all included studies, control wounds underwent placebo or were left untreated. The PRP group showed a better healing performance than the control group in each outcome. The effect size was statistically significant considering the primary outcome and the overall aggregation of the three outcomes. The effect size, although in favour of the treatment with PRP, was not significant considering the healing time and the number of healings. The overall heterogeneity was mild or moderate. Five studies reported a high risk of selection bias. The publication bias was always mild or absent. The results support the hypothesis of the positive effects of the PRP when compared to control groups in the treatment of experimentally-induced full-thickness skin wounds in animals. PRP can therefore be considered an effective adjunctive therapy in stimulating second intention healing of acute wounds in healthy animals.

The occurrence of biofilm in an equine experimental wound model of healing by secondary intention

In humans, biofilm is a well-known cause of delayed healing and low-grade inflammation of chronic wounds. In horses, biofilm formation in wounds has been studied to a very limited degree. The objective of this study was thus to investigate the occurrence of biofilm in equine experimental wounds healing by secondary intention. Tissue biopsies from non-contaminated, experimental excisional shoulder and limb wounds were obtained on day 1-2, day 7-10 and day 14-15 post-wounding. Limb wounds were either un-bandaged or bandaged to induce exuberant granulation tissue (EGT) formation and thereby impaired healing. Presence of biofilm in tissue biopsies was assessed by peptide nucleic acid fluorescence in situ hybridization (PNA FISH) and confocal laser scanning microscopy (CLSM). Bandaged limb wounds developed EGT and displayed delayed healing, while shoulder and un-bandaged limb wounds healed normally. Biofilm was detected in limb wounds only. At day 14-15 biofilm was significantly more prevalent in bandaged limb wounds than in un-bandaged limb wounds (P=0.003). Further, bandaged limb wounds had a statistically significant increase in biofilm burden from day 7-10 to day 14-15 (P=0.009). The finding that biofilm was most prevalent in bandaged limb wounds with EGT formation suggests that biofilm may be linked to delayed wound healing in horses, as has been observed in humans. The inability to clear bacteria could be related to hypoxia and low-grade inflammation in the EGT, but the interaction between biofilm forming bacteria and wound healing in horses needs further elucidation.

Short-term treatment of equine wounds with orf virus IL-10 and VEGF-E dampens inflammation and promotes repair processes without accelerating closure

Healing is delayed in limb wounds relative to body wounds of horses, partly because of sustained inflammation and inefficient angiogenesis. In laboratory animals, proteins derived from orf virus modulate these processes and enhance healing. We aimed to compare immune cell trafficking and the inflammatory, vascular, and epidermal responses in body and limb wounds of horses and then to investigate the impact of orf virus interleukin-10 and vascular endothelial growth factor-E on these processes. Standardized excisional wounds were created on the body and forelimb of horses and their progression monitored macroscopically until healed. Tissue samples were harvested to measure the expression of genes regulating inflammation and repair (quantitative polymerase chain reaction) and to observe epithelialization (histology), innate immune cell infiltration, and angiogenesis (immunofluorescence). Delayed healing of limb wounds was characterized by intensified and extended pro-inflammatory signaling and exacerbated innate immune response, concomitant with the absence of anti-inflammatory eIL-10. Blood vessels were initially more permeable and then matured belatedly, concomitant with retarded production of angiogenic factors. Epithelial coverage was achieved belatedly in limb wounds. Viral proteins were administered to wounds of one body and one limb site/horse at days 1-3, while wounds at matching sites served as controls. Treatment dampened pro-inflammatory gene expression and the innate immune response in all wounds. It also improved angiogenic gene expression, but primarily in body wounds, where it altered blood vessel density and myofibroblast persistence. Moreover, the viral proteins increased epithelialization of all wounds. The short-term viral protein therapy did not, however, improve the healing rate of wounds in either location, likely due to suboptimal dosing. In conclusion, we have further detailed the processes contributing to protracted healing in limb wounds of horses and shown that short-term administration of viral proteins exerts several promising though transient effects that, if optimized, may positively influence healing.