A novel murine island skin flap for ischemic preconditioning

A snake cathelicidin enhances transcription factor EB-mediated autophagy and alleviates ROS-induced pyroptosis after ischaemia-reperfusion injury of island skin flaps

BACKGROUND AND PURPOSE

Ischaemia-reperfusion (I/R) injury is a major contributor to skin flap necrosis, which presents a challenge in achieving satisfactory therapeutic outcomes. Previous studies showed that cathelicidin-BF (BF-30) protects tissues from I/R injury. In this investigation, BF-30 was synthesized and its role and mechanism in promoting survival of I/R-injured skin flaps explored.

EXPERIMENTAL APPROACH

Survival rate analysis and laser Doppler blood flow analysis were used to evaluate I/R-injured flap viability. Western blotting, immunofluorescence, TdT-mediated dUTP nick end labelling (TUNEL) and dihydroethidium were utilized to examine the levels of apoptosis, pyroptosis, oxidative stress, transcription factor EB (TFEB)-mediated autophagy and molecules related to the adenosine 5'-monophosphate-activated protein kinase (AMPK)-transient receptor potential mucolipin 1 (TRPML1)-calcineurin signalling pathway.

KEY RESULTS

The outcomes revealed that BF-30 enhanced I/R-injured island skin flap viability. Autophagy, oxidative stress, pyroptosis and apoptosis were related to the BF-30 capability to enhance I/R-injured flap survival. Improved autophagy flux and tolerance to oxidative stress promoted the inhibition of apoptosis and pyroptosis in vascular endothelial cells. Activation of TFEB increased autophagy and inhibited endothelial cell oxidative stress in I/R-injured flaps. A reduction in TFEB level led to a loss of the protective effect of BF-30, by reducing autophagy flux and increasing the accumulation of reactive oxygen species (ROS) in endothelial cells. Additionally, BF-30 modulated TFEB activity via the AMPK-TRPML1-calcineurin signalling pathway.

CONCLUSION AND IMPLICATIONS

BF-30 promotes I/R-injured skin flap survival by TFEB-mediated up-regulation of autophagy and inhibition of oxidative stress, which may have possible clinical applications.

Pretreatment with platelet-rich plasma protects against ischemia-reperfusion induced flap injury by deactivating the JAK/STAT pathway in mice

BACKGROUND

Ischemia-reperfusion (I/R) injury is a major cause of surgical skin flap compromise and organ dysfunction. Platelet-rich plasma (PRP) is an autologous product rich in growth factors, with tissue regenerative potential. PRP has shown promise in multiple I/R-induced tissue injuries, but its effects on skin flap injury remain unexplored.

METHODS

We evaluated the effects of PRP on I/R-injured skin flaps, optimal timing of PRP administration, and the involved mechanisms.

RESULTS

PRP protected against I/R-induced skin flap injury by improving flap survival, promoting blood perfusion and angiogenesis, suppressing oxidative stress and inflammatory response, and reducing apoptosis, at least partly via deactivating Janus kinase (JAK)-signal transducers and activators of transcription (STAT) signalling pathway. PRP given before ischemia displayed overall advantages over that given before reperfusion or during reperfusion. In addition, PRP pretreatment had a stronger ability to reverse I/R-induced JAK/STAT activation and apoptosis than AG490, a specific inhibitor of JAK/STAT signalling.

CONCLUSIONS

This study firstly demonstrates the protective role of PRP against I/R-injured skin flaps through negative regulation of JAK/STAT activation, with PRP pretreatment showing optimal therapeutic effects.

Determination of Flap Survival Isolated From Wound Bed Vasculature Using a Murine Axial Flap Model

Background: Axial pattern flaps are a common reconstructive option following resection of soft tissue malignancies. We determine the early dependence of an axial flap on wound bed vasculature by isolating the underlying wound bed and depriving contact with the overlying flap. Materials and Methods: Mice were divided into 5 groups: No silicone (n = 7), silicone in the proximal 50% of the wound bed (n = 8), silicone in the distal 50% of the wound bed (n = 5), silicone over the full length of the wound bed with pedicle preservation (n = 5), and silicone over the full length of the wound bed with pedicle sacrifice (n = 5). The pedicle was the lateral thoracic artery. Daily photographs were taken, and the percent of viable flap was determined using ImageJ© software (public domain JAVA image processing program, National Institute of Health, Bethesda, MA). Percent flap viability for each group was compared to the no silicone group, which acted as the reference. Results: Mean differences in percent flap necrotic area (with 95% confidence interval) compared to the no silicone group were -0.15% (-15.09 to 14.09), 2.07% (-5.26 to 9.39), 2.98% (-10.98 to 16.94), and 14.21% (0.48 to 27.94) for the full-length silicone with preserved pedicle, proximal silicone, distal silicone, and full-length silicone with sacrificed pedicle groups, respectively. The full-length silicone with sacrificed pedicle group had a significant difference in flap viability (P = .045) compared to the no silicone group. Conclusion: We investigate the role of the wound bed vasculature in a murine axial flap model and demonstrate that the wound bed vasculature is not essential for early distal flap survival.

Challenges faced in developing an ideal chronic wound model

INTRODUCTION

Chronic wounds are a major drain on healthcare resources and can lead to substantial reductions in quality of life for those affected. Moreover, they often precede serious events such as limb amputations and premature death. In the long run, this burden is likely to escalate with an ageing population and lifestyle diseases such as obesity. Thus far, the identification of beneficial therapeutics against chronic wounds have been hindered by the lack of an ideal chronic wound animal model. Although animal models of delayed healing have been developed, none of these models fully recapitulate the complexity of the human chronic wound condition. Furthermore, most animals do not develop chronic wounds. Only the thoroughbred racehorse develops chronic ulcers.

AREAS COVERED

In this review, the different characteristics of chronic wounds that highlight its complexity are described. In addition, currently available models reflecting different aspects of chronic wound pathology and their relevance to human chronic wounds are discussed. This article concludes by listing relevant features representative of an ideal chronic wound model. Additionally, alternative approaches for the development of chronic wound models are discussed.

EXPERT OPINION

Delayed models of healing, including the streptozotocin diabetic model, skin flap model and magnet-induced IR models have emerged. While these models have been widely adopted for preclinical therapeutic testing, their relevance towards human chronic wounds remains debatable. In particular, current delayed healing models often fail to fully incorporate the key characteristics of chronic ulcers. Ultimately, more representative models are required to expedite the advancement of novel therapeutics to the clinic.

Hyperintensity of integrin-targeted fluorescence agent IntegriSense750 accurately predicts flap necrosis compared to Indocyanine green

BACKGROUND

Flap necrosis is a feared complication of reconstructive surgery. Current methods of prediction using Indocyanine green (ICG) lack specificity. IntegriSense750 is a fluorescence agent that binds sites of vascular remodeling. We hypothesized that IntegriSense750 better predicts flap compromise compared to ICG.

METHODS

Fifteen mice underwent lateral thoracic artery axial flap harvest. Mice received an injection of ICG (n = 7) or IntegriSense750 (n = 8) daily from postoperative days (POD) 0-3 and were imaged daily. Mean signal-to-background ratios quantified the change in fluorescence as necrosis progressed.

RESULTS

Mean signal-to-background ratio was significantly higher for IntegriSense750 compared to ICG on POD0 (1.47 ± 0.17 vs. 0.86 ± 0.21, p = 0.01) and daily through POD3 (2.12 ± 0.70 vs. 0.96 ± 0.29, p < 0.001).

CONCLUSIONS

IntegriSense750 demonstrates increased signal-to-background ratio at areas of flap distress compared to ICG which may increase identification of flap necrosis and improve patient outcomes.

Effectiveness of Different Surgical Flap Delay Methods and Their Systemic Toxicities

OBJECTIVE

The surgical flap delaying has been shown to be effective in preventing partial flap loss or in preparing larger flaps. However, there is no gold standard flap delay method in the literature. In this study, the authors aimed to compare 3 types of surgical delay methods to determine which model would increase more flap survival. The authors also investigated the effect of delay methods on circulating mononuclear leukocytes as a parameter of DNA damage.

METHODS

Twenty-four Sprague-Dawley male rats were divided into 4 groups. All subjects had a 10 × 3 cm modified McFarlane flap. Surface area measurements, biopsies, and blood samples were taken on the day of sacrification; 7th day for the control group and 14th day for delay groups.

RESULTS

Between incisional surgery delay groups, a significant difference was found in necrosis and apoptosis in the bipedicled group, and only necrosis in the tripedicled group compared to the control. In terms of DNA damage, it was found higher in all experimental groups than in the control group.

CONCLUSIONS

Both incisional surgical delay procedures' results were meaningfully effective when only incisions were made without the elevation of flaps. In conclusion, bipedicled incisional surgical delay seems to be the most effective method in McFarlane experimental flap model whereas two-staged surgeries may increase the risk of systemic toxicity.

Mannose-binding lectin (MBL) and the lectin complement pathway play a role in cutaneous ischemia and reperfusion injury

Objectives

Cutaneous ischemia/reperfusion (CI/R) injury has shown to play a significant role in chronic wounds such as decubitus ulcers, diabetic foot ulcers, atherosclerotic lesions, and venous stasis wounds. CI/R also plays a role in free tissue transfer in reconstructive microsurgery and has been linked to clinical burn-depth progression after thermal injury. While the role of the complement system has been elucidated in multiple organ systems, evidence is lacking with respect to its role in the skin. Therefore, we evaluated the role of the complement system in CI/R injury.

Methods

Using a single pedicle skin flap mouse model of acute CI/R, we performed CI/R in wild-type (WT) mice and complement knock out (KO) mice, deficient in either C1q (C1q KO; classical pathway inhibition), mannose-binding lectin (MBL null; lectin pathway inhibition) or factor B (H2Bf KO; alternative pathway inhibition). Following 10 h ischemia and 7 days reperfusion, mice were sacrificed, flaps harvested and flap viability assessed via Image J software. The flap necrotic area was expressed as % total flap area. In another group, mice were sacrificed following CI/R with 10 h ischemia and 48 h reperfusion. Two cranial skin flap samples were taken for gene expression analysis of IL1b, IL6, TNFα, ICAM1, VCAM1, IL10, IL13 using real-time polymerase chain reaction (RT-PCR).

Results

Following CI/R, MBL null mice had a statistically significant smaller %necrotic flap area compared to WT mice (10.6 vs. 43.1%; p<0.05) suggesting protection from CI/R. A significantly reduced mean %necrotic flap area was not seen in either C1q KO or H2Bf KO mice relative to WT (22.9 and 31.3 vs. 43.1%; p=0.08 and p=0.244, respectively). There were no statistically significant differences between groups for markers of inflammation (TNFα, ICAM1, VCAM1, IL1b, IL6). In contrast, mRNA levels of IL10, a regulator of inflammation, were significantly increased in the MBL null group (p=0.047).

Conclusions

We demonstrated for the first time a significant role of MBL and the lectin complement pathway in ischemia/reperfusion injury of the skin and a potential role for IL10 in attenuating CI/R injury, as IL10 levels were significantly increased in the tissue from the CI/R-protected MBL null group.

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.

Laboratory Models for the Study of Normal and Pathologic Wound Healing

Current knowledge of wound healing is based on studies using various in vitro and in vivo wound models. In vitro models allow for biological examination of specific cell types involved in wound healing. In vivo models generally provide the full spectrum of biological responses required for wound healing, including inflammation and angiogenesis, and provide cell-cell interactions not seen in vitro. In this review, the authors aim to delineate the most relevant wound healing models currently available and to discuss their strengths and limitations in their approximation of the human wound healing processes to aid scientists in choosing the most appropriate wound healing models for designing, testing, and validating their experiments.

A new lateral thoracic artery perforator flap design with multiple vascular territories in rats

BACKGROUND

To describe a new design for an extended lateral thoracic artery (LTA) perforator flap and investigate its anatomical, dynamic, and potential territories.

MATERIALS AND METHODS

To assess vascular territories, rats were randomized according to LTA perforator flap type into the surgical groups A, hemidorsal island flap; B, entire dorsal island flap; and C, reduced-size dorsal island flap.

RESULTS

On postsurgical day 7, the surviving flap areas were 95%, 92%, and 89% in groups A, B, and C, respectively. Necrosis most commonly occurred in the contralateral LTA territories in groups B and C. The immunoreactivities of intercellular adhesion molecule 1 and vascular endothelial growth factor receptor 2 in dynamic territories, as choke vessel markers, were increased.

CONCLUSIONS

We clarified the LTA perforator flap nomenclature and defined its pedicle course and anastomosing patterns; furthermore, we demonstrated that the LTA perforator did not anastomose with its counterpart because of its unidirectional, oblique, and craniocaudal course. The LTA perforator flap was found to be a good model comprising multiple vascular territories and exhibiting continuous necrosis.

Role of the p38 mitogen-activated protein kinase signaling pathway in estrogen-mediated protection following flap ischemia-reperfusion injury

Ischemia-reperfusion (I/R) injury often occurs during skin flap transplantation and results in tissue damage. Although estrogen treatment significantly alleviates this I/R injury-induced damage, the detailed molecular mechanism is not clear. In this study, a superficial epigastric artery flap I/R injury model was created in adult Wistar rats. Severe necrosis was observed in skin tissue after I/R injury. Histological examination of skin tissue revealed that I/R injury damages skin structure and results in neutrophil infiltration. Inflammation-related parameters, including neutrophil count, tumor necrosis factor-α, and interleukin-10 levels, were increased due to I/R injury. These pathological phenomena were reduced by estradiol treatment. Further investigation found that I/R injury triggers the p38 mitogen-activated protein kinase (p38-MAPK) pathway. The expression levels of p38-MAPK and phosphorylated p38-MAPK were increased after I/R injury. Estradiol increased the expression level of MAPK phosphatase-2, a putative phosphatase of p38, and reduced the levels of p38-MAPK and phosphorylated p38-MAPK. These results suggest that estradiol can improve skin flap survival, possibly by inhibiting neutrophil infiltration and the expression of p38-MAPK. This study provides an explanation for how estrogen alleviates I/R injury-induced damage that occurs during skin flap transplantation. In a rat pathological model, I/R injury leads to skin necrosis, skin structure damage, neutrophil infiltration, and inflammatory cytokine secretion, which are probably downstream effects of activation of the p38-MAPK pathway. On the other hand, estradiol treatment triggers the expression of MAPK phosphatase-2, a putative phosphatase of p38-MAPK, and reduced all examined pathological phenomena. Therefore, estrogen may reduce the deleterious effect of I/R injury on skin flap transplantation through modulating the p38-MAPK pathway.

Thioredoxin Protects Skin Flaps from Ischemia-Reperfusion Injury: A Novel Prognostic and Therapeutic Target

BACKGROUND

Ischemia-reperfusion injury is inevitable during free-tissue transfer, causing oxidative damage and extensive apoptosis. Thioredoxin is an endogenous protein with antioxidant and antiapoptotic activity in a variety of tissues. This study aims to investigate the protective effects of human thioredoxin-1 on ischemia-reperfusion flaps, and its clinical application value.

METHODS

Sixteen clinical specimens of ischemia-reperfusion flaps were collected and assessed for apoptosis and thioredoxin-1 expression. Eighty mice were administered recombinant human thioredoxin-1 or saline intraperitoneally for 5 days before ischemia-reperfusion. Half of the mice were killed 24 hours after reperfusion. The flap tissues were harvested and detected for the changes of morphology, apoptosis, redox condition, and relative protein expression. The flap survival percentage of the remaining mice was consecutively observed within 7 days of reperfusion.

RESULTS

Thioredoxin-1 abundance was negatively correlated with ischemia-reperfusion-induced apoptosis in human samples and animal models. The survival rate of the ischemia-reperfusion flaps in mice increased significantly following recombinant human thioredoxin-1 pretreatment. Mitigated tissue damage, reduced apoptosis, and more antioxidant activity were observed in recombinant human thioredoxin-1-pretreated flaps. Western blot analysis revealed thioredoxin-1 depletion and a significant increase in apoptosis signal-regulating kinase 1, p-p38, and cleaved caspase-3 abundance in the ischemia-reperfusion flaps, whereas supplementation of recombinant human thioredoxin-1 significantly reduced the apoptosis-related protein expression.

CONCLUSIONS

Thioredoxin-1 exerts its flap-protective role through redox regulation of reactive oxygen species scavenging and antiapoptotic signaling. The authors' research provides evidence that thioredoxin-1 may serve as a potential prognostic and therapeutic target for skin flap ischemia-reperfusion injury.

Clinical challenges of chronic wounds: searching for an optimal animal model to recapitulate their complexity

The efficient healing of a skin wound is something that most of us take for granted but is essential for surviving day-to-day knocks and cuts, and is absolutely relied on clinically whenever a patient receives surgical intervention. However, the management of a chronic wound – defined as a barrier defect that has not healed in 3 months – has become a major therapeutic challenge throughout the Western world, and it is a problem that will only escalate with the increasing incidence of conditions that impede wound healing, such as diabetes, obesity and vascular disorders. Despite being clinically and molecularly heterogeneous, all chronic wounds are generally assigned to one of three major clinical categories: leg ulcers, diabetic foot ulcers or pressure ulcers. Although we have gleaned much knowledge about the fundamental cellular and molecular mechanisms that underpin healthy, acute wound healing from various animal models, we have learned much less about chronic wound repair pathology from these models. This might largely be because the animal models being used in this field of research have failed to recapitulate the clinical features of chronic wounds. In this Clinical Puzzle article, we discuss the clinical complexity of chronic wounds and describe the best currently available models for investigating chronic wound pathology. We also assess how such models could be optimised to become more useful tools for uncovering pathological mechanisms and potential therapeutic treatments.

The effect of platelet rich plasma on angiogenesis in ischemic flaps in VEGFR2-luc mice

To improve skin flap healing, one promising strategy in reconstructive surgery might be to optimize platelet rich plasma (PRP) bioactivity and the ischemia-altered expression of genes. We studied both the effect of PRP on ischemic flaps, and whether in vivo bioluminescence imaging (BLI) is a suitable method for the longitudinal monitoring of angiogenesis in surgical wounds. Axial murine skin flaps were created in four experimental groups. In vivo measurements of VEGFR2 expression levels were made every other day until the 14th day. The local VEGF level and microvessel density were quantified on the 14th day via ELISA and immunohistochemistry, and flap survival rates were measured. We demonstrated that PRP and induced ischemia have a beneficial influence on angiogenesis and flap healing. Combining the two resulted in a significantly robust increase in angiogenesis and flap survival rate that was corroborated by bioluminescence imaging of VEGFR2 activity. This study shows that angiogenic effects of PRP may be potentialized by the stimulus of induced ischemia during free flap harvesting, and thus the two procedures appear to have a synergistic effect on flap healing. This study further demonstrates that BLI of modulated genes in reconstructive surgery is a valuable model for longitudinal in vivo evaluation of angiogenesis.

Development of a mouse model of abdominal cutaneous flaps for breast reconstruction

Autologous tissue transfer, in addition to replacing tissue that was lost during injury or surgery, offers women an excellent option to improve cosmetic appearance and self-confidence following mastectomy due to breast cancer. However, flap necrosis is a complication in obese patients undergoing this procedure. We created a mouse model to study the flap-related complications that leads to decreased flap survival in autologous breast reconstruction.

An anisotropic, hyperelastic model for skin: experimental measurements, finite element modelling and identification of parameters for human and murine skin

The mechanical characteristics of skin are extremely complex and have not been satisfactorily simulated by conventional engineering models. The ability to predict human skin behaviour and to evaluate changes in the mechanical properties of the tissue would inform engineering design and would prove valuable in a diversity of disciplines, for example the pharmaceutical and cosmetic industries, which currently rely upon experiments performed in animal models. The aim of this study was to develop a predictive anisotropic, hyperelastic constitutive model of human skin and to validate this model using laboratory data. As a corollary, the mechanical characteristics of human and murine skin have been compared. A novel experimental design, using tensile tests on circular skin specimens, and an optimisation procedure were adopted for laboratory experiments to identify the material parameters of the tissue. Uniaxial tensile tests were performed along three load axes on excised murine and human skin samples, using a single set of material parameters for each skin sample. A finite element model was developed using the transversely isotropic, hyperelastic constitutive model of Weiss et al. (1996) and was embedded within a Veronda-Westmann isotropic material matrix, using three fibre families to create anisotropic behaviour. The model was able to represent the nonlinear, anisotropic behaviour of the skin well. Additionally, examination of the optimal material coefficients and the experimental data permitted quantification of the mechanical differences between human and murine skin. Differences between the skin types, most notably the extension of the skin at low load, have highlighted some of the limitations of murine skin as a biomechanical model of the human tissue. The development of accurate, predictive computational models of human tissue, such as skin, to reduce, refine or replace animal models and to inform developments in the medical, engineering and cosmetic fields, is a significant challenge but is highly desirable. Concurrent advances in computer technology and our understanding of human physiology must be utilised to produce more accurate and accessible predictive models, such as the finite element model described in this study.