Skin 11ß-hydroxysteroid dehydrogenase type 1 enzyme expression regulates burn wound healing and can be targeted to modify scar characteristics.

Background: Excessive scarring and fibrosis are the most severe and common complications of burn injury. Prolonged exposure to high levels of glucocorticoids detrimentally impacts on skin, leading to skin thinning and impaired wound healing. Skin can generate active glucocorticoids locally through expression and activity of the 11ß-hydroxysteroid dehydrogenase type 1 enzyme (11ß-HSD1). We hypothesised that burn injury would induce 11ß-HSD1 expression and local glucocorticoid metabolism, which would have important impacts on wound healing, fibrosis and scarring. We additionally proposed that pharmacological manipulation of this system could improve aspects of post-burn scarring. Methods: Skin 11ß-HSD1 expression in burns patients and mice was examined. The impacts of 11ß-HSD1 mediating glucocorticoid metabolism on burn wound healing, scar formation and scar elasticity and quality were additionally examined using a murine 11ß-HSD1 genetic knockout model. Slow-release scaffolds containing therapeutic agents, including active and inactive glucocorticoids, were developed and pre-clinically tested in mice with burn injury. Results: We demonstrate that 11ß-HSD1 expression levels increased substantially in both human and mouse skin after burn injury. 11ß-HSD1 knockout mice experienced faster wound healing than wild type mice but the healed wounds manifested significantly more collagen deposition, tensile strength and stiffness, features characteristic of excessive scarring. Application of slow-release prednisone, an inactive glucocorticoid, slowed the initial rate of wound closure but significantly reduced post-burn scarring via reductions in inflammation, myofibroblast generation, collagen production and scar stiffness. Conclusions: Skin 11ß-HSD1 expression is a key regulator of wound healing and scarring after burn injury. Application of an inactive glucocorticoid capable of activation by local 11ß-HSD1 in skin slows the initial rate of wound closure but significantlyimproves scar characteristics post burn injury.

Role of wound microbiome, strategies of microbiota delivery system and clinical management.

Delayed wound healing is one of the most global public health threats affecting nearly 100 million people each year, particularly the chronic wounds. Many confounding factors such as aging, diabetic disease, medication, peripheral neuropathy, immunocompromises or arterial and venous insufficiency hyperglycaemia are considered to inhibit wound healing. Therapeutic approaches for slow wound healing include anti-infection, debridement and the use of various wound dressings. However, the current clinical outcomes are still unsatisfied. In this review, we discuss the role of skin and wound commensal microbiota in the different healing stages, including inflammation, cell proliferation, re-epithelialization and remodelling phase, followed by multiple immune cell responses to commensal microbiota. Current clinical management in treating surgical wounds and chronic wounds was also reviewed together with potential controlled delivery systems which may be utilized in the future for the topical administration of probiotics and microbiomes. This review aims to introduce advances, novel strategies, and pioneer ideas in regulating the wound microbiome and the design of controlled delivery systems.

Low-protein diet accelerates wound healing in mice post-acute injury.

BACKGROUND: Wound healing processes are influenced by macronutrient intake (protein, carbohydrate and fat). The most favourable diet for cutaneous wound healing is not known, although high-protein diets are currently favoured clinically. This experimental study investigates the optimal macronutrient balance for cutaneous wound healing using a mouse model and the Geometric Framework, a nutrient modelling method, capable of analyzing the individual and interactive effects of a wide spectrum of macronutrient intake. METHODS: Two adjacent and identical full-thickness skin excisions (1 cm2) were surgically created on the dorsal area of male C57BL/6 mice. Mice were then allocated to one of 12 high-energy diets that varied in protein, carbohydrate and fat content. In select diets, wound healing processes, cytokine expression, energy expenditure, body composition, muscle and fat reserves were assessed. RESULTS: Using the Geometric Framework, we show that a low-protein intake, coupled with a balanced intake of carbohydrate and fat is optimal for wound healing. Mice fed a low-protein diet progressed quickly through wound healing stages with favourable wound inflammatory cytokine expression and significantly accelerated collagen production. These local processes were associated with an increased early systemic inflammatory response and a higher overall energy expenditure, related to metabolic changes occurring in key macronutrient reserves in lean body mass and fat depots. CONCLUSIONS: The results suggest that a low-protein diet may have a greater potential to accelerate wound healing than the current clinically used high-protein diets.

The contradictory role of androgens in cutaneous and major burn wound healing.

Wound healing is a complex process involving four overlapping phases: haemostasis, inflammation, cell recruitment and matrix remodeling. In mouse models, surgical, pharmacological and genetic approaches targeting androgen actions in skin have shown that androgens increase interleukin-6 and tumor necrosis factor-α production and reduce wound re-epithelization and matrix deposition, retarding cutaneous wound healing. Similarly, clinical studies have shown that cutaneous wound healing is slower in men compared to women. However, in major burn injury, which triggers not only local wound-healing processes but also systemic hypermetabolism, the role of androgens is poorly understood. Recent studies have claimed that a synthetic androgen, oxandrolone, increases protein synthesis, improves lean body mass and shortens length of hospital stay. However, the possible mechanisms by which oxandrolone regulates major burn injury have not been reported. In this review, we summarize the current findings on the roles of androgens in cutaneous and major burn wound healing, as well as androgens as a potential therapeutic treatment option for patients with major burn injuries.

Geometric framework reveals that a moderate protein, high carbohydrate intake is optimal for severe burn injury in mice.

Nutritional therapy is a cornerstone of burns management. The optimal macronutrient intake for wound healing after burn injury has not been identified, although high-energy, high-protein diets are favoured. The present study aimed to identify the optimal macronutrient intake for burn wound healing. The geometric framework (GF) was used to analyse wound healing after a 10 % total body surface area contact burn in mice ad libitum fed one of the eleven high-energy diets, varying in macronutrient composition with protein (P5-60 %), carbohydrate (C20-75 %) and fat (F20-75 %). In the GF study, the optimal ratio for wound healing was identified as a moderate-protein, high-carbohydrate diet with a protein:carbohydrate:fat (P:C:F) ratio of 1:4:2. High carbohydrate intake was associated with lower mortality, improved body weight and a beneficial pattern of body fat reserves. Protein intake was essential to prevent weight loss and mortality, but a protein intake target of about 7 kJ/d (about 15 % of energy intake) was identified, above which no further benefit was gained. High protein intake was associated with delayed wound healing and increased liver and spleen weight. As the GF study demonstrated that an initial very high protein intake prevented mortality, a very high-protein, moderate-carbohydrate diet (P40:C42:F18) was specifically designed. The dynamic diet study was also designed to combine and validate the benefits of an initial very high protein intake for mortality, and subsequent moderate protein, high carbohydrate intake for optimal wound healing. The dynamic feeding experiment showed switching from an initial very high-protein diet to the optimal moderate-protein, high-carbohydrate diet accelerated wound healing whilst preventing mortality and liver enlargement.

Mouse models in burns research: Characterisation of the hypermetabolic response to burn injury.

OBJECTIVE: The aim of the study is to characterise burn induced hypermetabolism in a mouse model. SUMMARY BACKGROUND DATA: There are many mouse models of burn injury currently available however, their use in burns research is limited by the general assumption that post-burn hypermetabolism is difficult to study in these models. METHODS: Male Balb/c mice were subjected to either a small (1 cm2) or large (4 cm2) contact burn. The hypermetabolic response to burn injury was determined by measuring changes in basal energy expenditure. The hormonal and inflammatory mediators of hypermetabolism, and the catabolic alterations secondary to hypermetabolism were also examined. RESULTS: Post-burn hypermetabolism was induced in both models of small and large burn. However, large burns resulted in prolonged wound healing, a more pronounced and sustained increase in basal energy expenditure, and a greater stress and systemic inflammatory response with profound catabolic consequences. CONCLUSIONS: In the present study, we have successfully characterised the burn induced systemic hypermetabolic response in a mouse model of small and large burn. These models may prove useful for researchers studying the complex aetiology of hypermetabolism and interventions.