A novel model of human skin pressure ulcers in mice

A murine pressure ulcer model for evaluating persistence and treatment of Staphylococcus aureus infection

Chronic wounds, particularly pressure ulcers, pose significant healthcare challenges, especially in the elderly population. This study presents an experimental murine model of chronically infected pressure ulcers using a single cycle of magnet-induced ischemic injury combined with infection by bioluminescent Staphylococcus aureus. The model addresses previous limitations in studying pressure ulcer infection pathogenesis and evaluating treatment efficacy. By combining this model with in vivo imaging system (IVIS) technology, we achieved real-time, non-invasive monitoring of infection dynamics. This approach demonstrated persistent pressure ulcer wound infection and provided temporal and spatial data on infection status. To validate the model's utility, we evaluated the antimicrobial efficacy of TCP-25, a synthetic host defense peptide, delivered in a topical gel formulation. Our findings highlight the potential of this model for investigating wound infection mechanisms, bacterial persistence, and therapeutic interventions. This innovative approach represents a significant advancement in pressure ulcer research, offering new opportunities for developing effective treatment strategies and improving patient outcomes.

The Recovery of Epidermal Proliferation Pattern in Human Skin Xenograft

Abnormalities in epidermal keratinocyte proliferation are a characteristic feature of a range of dermatological conditions. These include hyperproliferative states in psoriasis and dermatitis as well as hypoproliferative states in chronic wounds. This emphasises the importance of investigating the proliferation kinetics under conditions of healthy skin and identifying the key regulators of epidermal homeostasis, maintenance, and recovery following wound healing. Animal models contribute to our understanding of human epidermal self-renewal. Human skin xenografting overcomes the ethical limitations of studying human skin during regeneration. The application of this approach has allowed for the identification of a single population of stem cells and both slowly and rapidly cycling progenitors within the epidermal basal layer and the mapping of their location in relation to rete ridges and hair follicles. Furthermore, we have traced the dynamics of the proliferation pattern reorganization that occurs during epidermal regeneration, underlining the role of YAP activity in epidermal relief formation.

Recent advances in the development of hydrogel dressings for the treatment of pressure ulcers/injuries

Pressure ulcers, also known as pressure injuries, are common conditions that result from chronic bedrest. These ulcers significantly affect quality of life and substantially burden individuals and society with health costs. The prevention and treatment of pressure ulcers is a primary concern for health care professionals. Dressings play a crucial role in the treatment of pressure ulcers. Hydrogels are innovative safe materials that show great promise for clinical applications. Recent research has demonstrated the potential of hydrogel dressings to promote the healing of pressure ulcers and chronic wounds. This review aims to summarize the mechanisms and effects of hydrogel dressings and to discuss considerations for their use in patients with pressure injuries under different circumstances. Hydrogel dressings, especially loaded with unique cargo, may represent promising new options for the treatment of pressure ulcers. However, additional clinical studies are urgently needed to validate the efficacy and accessibility of hydrogels in clinical practice.

Pressure injuries and biofilms: Microbiome, model systems and therapies

Chronic wounds have emerged as significant clinical problems owing to their increasing incidence and greater recognition of associated morbidity and socio-economic burden. They are defined as wounds that do not progress normally through the stages of healing in a timely and/or orderly manner. Pressure injuries, in particular, represent a serious problem for patients who are elderly or have limited mobility, such as wheelchair users or those who spend most of the day in bed. These injuries often result from prolonged pressure exerted on the skin over the bone. Treatment of pressure injuries is complex and costly. Emerging evidence suggests that the pressure injury microbiome plays a vital role in chronic wound formation and delaying wound healing. Additionally, antibiotics often fail due to the formation of resistant biofilms and the emergence of antimicrobial-resistant bacteria. In this review, we will summarise the current knowledge on: (a) biofilms and microbiomes in pressure injuries; (b) in vitro and in vivo model systems to study pressure injuries, and (c) current therapies and novel treatment approaches. Understanding the complex interactions between microbes and the host immune system in pressure injuries will provide valuable insights to improve patient outcomes.

Establishing a Xenograft Model with CD-1 Nude Mice to Study Human Skin Wound Repair

BACKGROUND

A significant gap exists in the translatability of small-animal models to human subjects. One important factor is poor laboratory models involving human tissue. Thus, the authors have created a viable postnatal human skin xenograft model using athymic mice.

METHODS

Discarded human foreskins were collected following circumcision. All subcutaneous tissue was removed from these samples sterilely. Host CD-1 nude mice were then anesthetized, and dorsal skin was sterilized. A 1.2-cm-diameter, full-thickness section of dorsal skin was excised. The foreskin sample was then placed into the full-thickness defect in the host mice and sutured into place. Xenografts underwent dermal wounding using a 4-mm punch biopsy after engraftment. Xenografts were monitored for 14 days after wounding and then harvested.

RESULTS

At 14 days postoperatively, all mice survived the procedure. Grossly, the xenograft wounds showed formation of a human scar at postoperative day 14. Hematoxylin and eosin and Masson trichome staining confirmed scar formation in the wounded human skin. Using a novel artificial intelligence algorithm using picrosirius red staining, scar formation was confirmed in human wounded skin compared with the unwounded skin. Histologically, CD31 + immunostaining confirmed vascularization of the xenograft. The xenograft exclusively showed human collagen type I, CD26 + , and human nuclear antigen in the human scar without any staining of these human markers in the murine skin.

CONCLUSION

The proposed model demonstrates wound healing to be a local response from tissue resident human fibroblasts and allows for reproducible evaluation of human skin wound repair in a preclinical model.

CLINICAL RELEVANCE STATEMENT

Radiation-induced fibrosis is a widely prevalent clinical phenomenon without a well-defined treatment at this time. This study will help establish a small-animal model to better understand and develop novel therapeutics to treat irradiated human skin.

Blank Spots in the Map of Human Skin: The Challenge for Xenotransplantation

Most of the knowledge about human skin homeostasis, development, wound healing, and diseases has been accumulated from human skin biopsy analysis by transferring from animal models and using different culture systems. Human-to-mouse xenografting is one of the fundamental approaches that allows the skin to be studied in vivo and evaluate the ongoing physiological processes in real time. Humanized animals permit the actual techniques for tracing cell fate, clonal analysis, genetic modifications, and drug discovery that could never be employed in humans. This review recapitulates the novel facts about mouse skin self-renewing, regeneration, and pathology, raises issues regarding the gaps in our understanding of the same options in human skin, and postulates the challenges for human skin xenografting.

Protocol for xenotransplantation of human skin and streptozotocin diabetes induction in immunodeficient mice to study impaired wound healing

Here, we present a protocol for the integration of human skin onto the backs of diabetic immunodeficient mice, providing a versatile in vivo model for mimicking and studying mechanisms involved in impaired cutaneous wound healing. This protocol includes instructions for the grafting of human skin, induction of diabetes using streptozotocin and wounding/post-wounding care of immunodeficient mice, as well as suggested downstream tissue analyses. This preclinical mouse model can be used to validate the efficacy of newly developed wound dressings. For complete details on the use and execution of this protocol, please refer to Theocharidis et al. (2022).1.

A fabric-based multifunctional sensor for the early detection of skin decubitus ulcers

Monitoring biosignals at the skin interface is necessary to suppress the potential for decubitus ulcers in immobile patients confined to bed. We develop conformally contacted, disposable, and breathable fabric-based electronic devices to detect skin impedance, applied pressure, and temperature, simultaneously. Based on the experimental evaluation of the multifunctional sensors, a combination of robust AgNW electrodes, soft ionogel capacitive pressure sensor, and resistive temperature sensor on fabric provides alarmed the initiation of early-stage decubitus ulcers without signal distortion under the external stimulus. For clinical verification, an animal model is established with a pair of magnets to mimic a human decubitus ulcers model in murine in vivo. The evidence of pressure-induced ischemic injury is confirmed with the naked eye and histological and molecular biomarker analyses. Our multifunctional integrated sensor detects the critical time for early-stage decubitus ulcer, establishing a robust correlation with the biophysical parameters of skin ischemia and integrity, including temperature and impedance.

Novel therapeutic targets for diabetes-related wounds or ulcers: an update on preclinical and clinical research

INTRODUCTION

Diabetes-related wounds, particularly diabetes-related foot ulcers, are mainly caused by lack of foot sensation and high plantar tissue stress secondary to peripheral neuropathy, ischemia secondary to peripheral artery disease, and dysfunctional wound healing. Current management of diabetes-related wounds involves the offloading of high foot pressures and the treatment of ischemia through revascularization. Despite these treatments, the global burden of diabetes-related wounds is growing, and thus, novel therapies are needed. The normal wound healing process is a coordinated remodeling process orchestrated by fibroblasts, endothelial cells, phagocytes, and platelets, controlled by an array of growth factors. In diabetes-related wounds, these coordinated processes are dysfunctional. The past animal model and human research suggest that prolonged wound inflammation, failure to adequately correct ischemia, and impaired wound maturation are key therapeutic targets to improve diabetes-related wound healing.

AREAS COVERED

This review summarizes recent preclinical and clinical research on novel diabetes-related wound treatments. Animal models of diabetes-related wounds and recent studies testing novel therapeutic agents in these models are described. Findings from clinical trials are also discussed. Finally, challenges to identifying and implementing novel therapies are described.

EXPERT OPINION

Given the growing volume of promising drug therapies currently under investigation, it is expected within the next decade, that diabetes-related wound treatment will be transformed.

Mouse Models for Human Skin Transplantation: A Systematic Review

Immunodeficient mouse models with human skin xenografts have been developed in the past decades to study different conditions of the skin. Features such as follow-up period and size of the graft are of different relevance depending on the purpose of an investigation. The aim of this study is to analyze the different mouse models grafted with human skin. A systematic review of the literature was performed in line with the PRISMA statement using MEDLINE/PubMed databases from January 1970 to June 2020. Articles describing human skin grafted onto mice were included. Animal models other than mice, skin substitutes, bioengineered skin, postmortem or fetal skin, and duplicated studies were excluded. The mouse strain, origin of human skin, graft dimensions, follow-up of the skin graft, and goals of the study were analyzed. Ninety-one models were included in the final review. Five different applications were found: physiology of the skin (25 models, mean human skin graft size 1.43 cm2 and follow-up 72.92 days), immunology and graft rejection (17 models, mean human skin graft size 1.34 cm2 and follow-up 86 days), carcinogenesis (9 models, mean human skin graft size 1.98 cm2 and follow-up 253 days), skin diseases (25 models, mean human skin graft size 1.55 cm2 and follow-up 86.48 days), and would healing/scars (15 models, mean human skin graft size 2.54 cm2 and follow-up 129 days). The follow-up period was longer in carcinogenesis models (253 ± 233.73 days), and the skin graft size was bigger in wound healing applications (2.54 ± 3.08 cm2). Depending on the research application, different models are suggested. Careful consideration regarding graft size, follow-up, immunosuppression, and costs should be analyzed and compared before choosing any of these mouse models. To our knowledge, this is the first systematic review of mouse models with human skin transplantation.

Histological and clinical evaluation of wound healing in pressure ulcers: a novel animal model

OBJECTIVE

Pressure ulcers (PUs) are a major healthcare problem, commonly associated with older people, patients who are bedbound and patients with diabetes. The impact of PUs can decrease patients' quality of life, and lead to high morbidity and mortality rates. In this study, we aimed to describe a novel PU model that simulates pressure ulcers in humans to provide a research tool for new drug testing.

METHOD

Diabetes was induced using streptozocin in 75 adult Sprague Dawley rats. To create the PU, skin was sandwiched between two magnets, one of them implanted below the panniculus carnosus muscle and the other above the skin. The model was tested on nondiabetic rats and diabetic rats, each with pressure ulcers, compared to nondiabetic rats with excisional wounds.

RESULTS

Results showed that the PU model in diabetic (p-value<0.000001) and non-diabetic rats (p-value<0.05) exhibited significantly delayed healing (no healing over 21 days) compared with the excisional wound that was completely healed by day 21.

CONCLUSION

Diabetic rats showed significant changes in intact skin compared with non-diabetic rats, as well as a significant delay in the healing process compared with the non-diabetic group. By effectively impairing the skin contraction otherwise seen in the rats, and thereby delaying healing and making it similar to that seen in hard-to-heal PUs in humans, this model provides an effective tool for wound healing research.

Histological and clinical evaluation of wound healing in pressure ulcers: a novel animal model

OBJECTIVE

Pressure ulcers (PUs) are a major healthcare problem, commonly associated with older people, patients who are bedbound and patients with diabetes. The impact of PUs can decrease patients' quality of life, and lead to high morbidity and mortality rates. In this study, we aimed to describe a novel PU model that simulates pressure ulcers in humans to provide a research tool for new drug testing.

METHOD

Diabetes was induced using streptozocin in 75 adult Sprague Dawley rats. To create the PU, skin was sandwiched between two magnets, one of them implanted below the panniculus carnosus muscle and the other above the skin. The model was tested on nondiabetic rats and diabetic rats, each with pressure ulcers, compared to nondiabetic rats with excisional wounds.

RESULTS

Results showed that the PU model in diabetic (p-value<0.000001) and non-diabetic rats (p-value<0.05) exhibited significantly delayed healing (no healing over 21 days) compared with the excisional wound that was completely healed by day 21.

CONCLUSION

Diabetic rats showed significant changes in intact skin compared with non-diabetic rats, as well as a significant delay in the healing process compared with the non-diabetic group. By effectively impairing the skin contraction otherwise seen in the rats, and thereby delaying healing and making it similar to that seen in hard-to-heal PUs in humans, this model provides an effective tool for wound healing research.

Experimental animal modelling for pressure injury: A systematic review

INTRODUCTION

Pressure injury (PI) is a potentially serious condition that is often a consequence of other medical illnesses. It remains a challenge for the clinicians and the researcher to fully understand and develop a technique for comprehending pathogenicity, prevention and treatment. Several animal models have been created to understand the multifaceted cellular and biochemical processes of PI. There are numerous known intrinsic and extrinsic factors influencing the recovery of PI. Some of the important factors are friction, spinal cord injury, diabetes, nutrition, aging, infection, medication, obesity and vascular diseases. The dearth of optimal, pre-clinical animal models capable of mimicking the human PI remains a major challenge for its cure. An ideal animal model must endeavour the reproducibility, clinical significance, and most importantly effective translation into clinical use.

METHODS

In this current systematic review, a methodological literature review was conducted on the PRISMA guidelines. PubMed/Medline, Research Scholar and Science Direct databases were searched. We conferred the animal models like mice, rats, pigs and dogs used in the PI experiments between January 1980 to January 2021. Typically, methods like Ischemia-reperfusion (IR), monoplegia pressure sore and mechanical non-invasive have been discussed. These were used to generate pressure injuries in small and large animal models.

RESULTS AND CONCLUSION

Different animal models (mouse, rat, pig, dog) were evaluated based on ease of handling, availability for research, their size, skin type and the technical skills required. Studies suggest that mice and rats are the best-suited animals as their skin healing by contraction resembles the skin healing in humans. In most of the studies with mice and rats, the time taken for the recovery was between 1 and 3 weeks. Further, various techniques discussed in the current systematics review, supports the statement that the Ischemia-reperfusion (IR) method is the most suited method to study pressure injury. It is a controlled method that can develop different stages of PI and does not require any specialized setup for the application.

Evolution of ischemia and neovascularization in a murine model of full thickness human wound healing

Translation of wound healing research is limited by the lack of an appropriate animal model, due to the anatomic and wound healing differences in animals and humans. Here, we characterize healing of grafted, full-thickness human skin in an in vivo model of wound healing. Full-thickness human skin, obtained from reconstructive operations, was grafted onto the dorsal flank of NOD.Cg-KitW41J Tyr + Prkdcscid Il2rgtm1Wjl /ThomJ mice. The xenografts were harvested 1 to 12 weeks after grafting, and histologic analyses were completed for viability, neovascularization, and hypoxia. Visual inspection of the xenograft shows drying and sloughing of the epidermis starting at week four. By week 12, the xenograft appears healed but has lost 63.05 ± 0.24% of the initial graft size. There is histologic evidence of epidermolysis as early as 2 weeks, which progresses until week 4, when new epidermis appears from the wound edges. Epidermal regeneration is complete by week 12, although the epidermis appears hypertrophied. An initial increase of infiltrating immune mouse cells into the xenograft normalizes to baseline 6 months after grafting. Neovascularization, as evidenced by positive staining for the proteins human CD31 and alpha smooth muscle actin, is present as early as 2 weeks after grafting at the interface between the xenograft and the mouse tissue. CD31 and alpha smooth muscle actin staining increased throughout the xenograft over the 12 weeks, leading to greater viability of the tissue. Likewise, there is increased Hypoxia Inducible Factor 1-alpha expression at the interface of viable and nonviable tissue, which suggest a hypoxia-driven process causing early graft loss. These findings illustrate human skin wound healing in an ischemic environment, providing a timeline for use of full thickness human skin after grafting in a murine model to study mechanisms underlying human skin wound healing.

Chronological changes in rat heel skin following depressurization of pressure ulcer-like dermal lesions

In our previous study, we proposed an animal model in which pressure ulcer-like dermal lesions can be produced by denervation of the sciatic nerve and application of a pressure load to rat heel skin. In the present study, we divided these animals into non-treated and pressure loading groups, and initiated hindlimb unloading (depressurization) by tail suspension at 1, 3, 5, 7, and 14 days after inflicting lesions (1-14d pressurization groups). Chronological changes in heel lesions were examined morphologically in all treatment groups after 1, 3, 7, 14, 28, and 40 days. Open dermal lesions were formed by 14 days in the loading group and numerous macrophages were present. In the 14d pressurization group, numerous macrophages were still distributed in and around lesions and Vascular endothelial cell growth factor (VEGF) expression was strongly detected by 3 days, but a thin germinal layer began to appear and CD68-positive macrophages and VEGF immunoreactions decreased gradually by 7 days later. By 14 days after depressurization, the germinal layer was repaired, and macrophages and immunoreactions of VEGF were similar to those of non-treated skin. These chronological changes were similar to those in human pressure ulcers, but from 5d after depressurization, different chronological changes were observed. Specifically, epidermis was thickened and macrophages were hardly detected at 5 days in the loading group, but the epidermis disappeared by 1 day in the 5d pressurization group. Subsequently, numerous macrophages aggregated and VEGF expression was increased by 3 days, and the remaining healing process was similar to that in the 14d pressurization group. Even when unloading was performed during the early stages (5d pressurization group), the epidermis disappeared and macrophages were then distributed before repair of the lesion was observed. These results suggest that earlier migration of macrophages to skin lesions might be associated with rapid wound healing.

Local Growth Hormone Therapy for Pressure Ulcer Healing on a Human Skin Mouse Model

The growth hormone is involved in skin homeostasis and wound healing. We hypothesize whether it is possible to improve pressure ulcer (PU) healing by locally applying the recombinant human growth hormone (rhGH) in a human skin mouse model. Non-obese diabetic/severe combined immunodeficient mice (n = 10) were engrafted with a full-thickness human skin graft. After 60 days with stable grafts, human skin underwent three cycles of ischemia-reperfusion with a compression device to create a PU. Mice were classified into two groups: rhGH treatment group (n = 5) and control group (n = 5). In the rhGH group for local intradermal injections, each had 0.15 mg (0.5IU) applied to the PU edges, once per week for four weeks. Evaluation of the wound healing was conducted with photographic and visual assessments, and histological analysis was performed after complete wound healing. The results showed a healing rate twice as fast in the rhGH group compared to the control group (1.25 ± 0.33 mm2/day versus 0.61 ± 0.27 mm2/day; p-value < 0.05), with a faster healing rate during the first 30 days. The rhGH group showed thicker skin (1953 ± 457 µm versus 1060 ± 208 µm; p-value < 0.05) in the repaired area, with a significant decrease in collagen type I/III ratio at wound closure (62 days, range 60-70). Local administration of the rhGH accelerates PU healing in our model. The rhGH may have a clinical use in pressure ulcer treatment.

Human Reconstructed Skin in a Mouse Model

Currently, no ideal in vivo skin model, to exactly mimic the native human skin, has been utilized for laboratory and clinical application. Here, we describe a method to in vivo reconstitute a human skin model, so-called hRSK, by using culture-expanded skin cells. We grafted a mixture of dissociated human epidermal and dermal cells onto an excision wound on the back of immunodeficient mouse to generate the hRSK, and the hRSK, containing epidermis, dermis, and subcutis and also appendages such as hair follicles, histologically mirrors in situ human skin.