Thermal injury model in the rabbit ear with quantifiable burn progression and hypertrophic scar.

Hypertrophic scar is a major clinical outcome of deep-partial thickness to full thickness thermal burn injury. Appropriate animal models are a limitation to burn research due to the lack of, or access to, animal models which address the endpoint of hypertrophic scar. Lower species, such as rodents, heal mainly by contracture, which limits the duration of study. Higher species, such as pigs, heal more similarly to humans, but are associated with high cost, long duration for scar development, challenges in quantifying scar hypertrophy, and poor manageability. Here, we present a quantifiable deep-partial thickness burn model in the rabbit ear. Burns were created using a dry-heated brass rod for 10 and 20 seconds at 90 °C. At the time of eschar excision on day 3, excisional wounds were made on the contralateral ear for comparison. Burn wound progression, in which the wound size expands over time is a major distinction between excisional and thermal injuries, was quantified at 1 hour and 3 days after the injuries using calibrated photographs and histology and the size of the wounds was found to be unchanged from the initial wound size at 1 hour, but 10% in the 20 seconds burn wounds at 3 days. A quantifiable hypertrophic scar, measured by histology as the scar elevation index, was present in both 20 seconds burn wounds and excisional wounds at day 35. ImageJ measurements revealed that the 20 seconds burn wound scars were 22% larger than the excisional wound scars and the 20 seconds burn scar area measurements from histology were 26% greater than in the excisional wound scar. The ability to measure both burn progression and scar hypertrophy over a 35-day time frame suits this model to screening early intervention burn wound therapeutics or scar treatments in a burn-specific scar model.

Topically delivered adipose derived stem cells show an activated-fibroblast phenotype and enhance granulation tissue formation in skin wounds.

Multipotent mesenchymal stem cells (MSCs) are found in various tissues and can proliferate extensively in vitro. MSCs have been used in preclinical animal studies and clinical trials in many fields. Adipose derived stem cells (ASCs) have several advantages compared to other MSCs for use in cell-based treatments because they are easy to isolate with relative abundance. However, quantitative approaches for wound repair using ASCs have been limited because of lack of animal models which allow for quantification. Here, we addressed the effect of topically delivered ASCs in wound repair by quantitative analysis using the rabbit ear model. We characterized rabbit ASCs, and analyzed their multipotency in comparison to bone marrow derived-MSCs (BM-MSCs) and dermal fibroblasts (DFs) in vitro. Topically delivered ASCs increased granulation tissue formation in wounds when compared to saline controls, whereas BM-MSCs or DFs did not. These studies suggest that ASCs and BM-MSCs are not identical, though they have similar surface markers. We found that topically delivered ASCs are engrafted and proliferate in the wounds. We showed that transplanted ASCs exhibited activated fibroblast phenotype, increased endothelial cell recruitment, and enhanced macrophage recruitment in vivo.

Alteration of Smad3 signaling in ischemic rabbit dermal ulcer wounds.

Impaired reepithelialization is a hallmark of chronic, ischemic wounds; however, the pathogenesis of the delayed reepithelialization in these wounds remains poorly understood. Transforming growth factor beta is involved in both the normal and hypoxic wound-healing response and exogenous overexpression of Smad3, which has been known to accelerate reepithelialization. Recently, it was shown in the rabbit ear dermal ulcer model that Ad-Smad3 injection enhanced reepithelialization and granulation tissue formation suggesting a positive effect of Smad3 on wound healing. However, little is known about the role of Smad3 in the ischemic wound healing process. In this study, we examined the effect of Smad3 in an ischemic wound model. Ad-Smad3 or Ad-LacZ (10(8) pfu/wound) was injected into either ear of white New Zealand rabbits. Twenty-four hours later, these ears were rendered ischemic using an established model, and four 7 mm full-thickness punch wounds were made on each ear. Histological evaluation showed a significant increase in reepithelialization parameters in Ad-Smad3-transfected wounds (p<0.01). In contrast, granulation tissue parameters were not affected by Smad3 in ischemia. Smad4 and Smad7 mRNA-expression was not affected by Smad3 overexpression. Connective tissue growth factor protein was up-regulated under ischemic conditions but was unaffected by Smad3 transfection in both ischemic and nonischemic wounds. Our results suggest an enhancing effect of Smad3 on reepithelialization in an ischemic wound model that, in turn, might provide novel therapeutic options. Furthermore, the lack of alteration of Smad-dependent intermediates by Smad3 overexpression suggests the activation of Smad-independent pathways in ischemia.

[The expression of laminin in the intermingled skin transplantation of allograft and autograft].

OBJECTIVE: To explore the healing mechanism of full-thickness wound treating by the intermingled skin transplantation of large sheet allograft with autograft through studying the expression of laminin (LN). METHODS: Thirty-six SD rats with 10% to 15% of total body surface area (TBSA) full-thickness were made. After 3 days, the devitalized tissue were excised and transplanted a large sheet of allograft from Wistar rats and islets of autografts were implanted 3 days later. On day 3, 5, 7, 14, 21 after allografting, the expression of LN in the grafts were detected by immunohistochemistry. RESULTS: On the 7th day postallografting, LN, which played positive action of epidermal cell adhesion, still retained in the allodermis after the rejection of alloepidermis occurred. On the 14th day postallografting, there appeared scattered LN underneath the epidermal cells migrating from islets of autografts. On the 21st day postallografting, LN in the basement membrane of skin grafts had completely formed. CONCLUSION: The intermingled transplantation of large sheet allograft with autograft may provide components of basement membrane for wound healing, which may help to improve the appearance and function of skin.

[Establishment of an animal model with hypertrophic scar].

OBJECTIVE: To establish an animal model of hypertrophic scar on the rabbit ears and to observe the dynamic process of scar formation on the ventral side of the rabbit ears. METHODS: Full skin defect (2 cm x 5 cm in diameter) was created on the ventral side of 60 ears in 32 New Zealand white rabbits. 1% silver sulfadiazine cream was applied to the wounds, and the dressing was changed once a week till wound healing. Four ears without operation were taken as control. Wound healing under natural condition was observed continuously for 12 months after the operation. The scar proliferation on the rabbit ears was observed by light microscope and transmission electron microscope, and the scar index was determined by computer image analyzing system. RESULTS: The color, thickness and texture of the wounds on the rabbit ears after epithelization underwent a process of scar overgrowth, maturation and degeneration. The change in scar index was in accordance with the wax and wane of scar proliferation. CONCLUSION: The hypertrophic scar formed on the ventral side of rabbit ears after natural healing of full thickness skin wounds was similar to that in humans. The results indicated that this animal model was ideal for the study of the developmental mechanism of hypertrophic scars and for the evaluation of the efficacy of the prevention and treatment of hypertrophic scars.