In vivo rabbit hindquarter model for assessment of regional burn hypermetabolism

Large animal models of thermal injury

Burn injury results in a triad of inter-related adaptive responses: a systemic inflammatory response, a stress response, and a consequent hypermetabolic state which supports the former two. These pathological responses extend beyond the site of injury to affect distant organs and influence long-term outcomes in the patient. Animal models have proven valuable in advancing our understanding of mechanisms underlying the multifactorial manifestations of burn injury. While rodent models have been unprecedented in providing insights into signaling pathways, metabolic responses, protein turnover, cellular and molecular changes; small animal models do not replicate hypermetabolism, hyperinflammation, and wound healing after a burn injury as seen in humans. Herein, we provide a concise review of preferred large animal models utilized to understand burn pathophysiology based on organ systems and associated dysfunction. Additionally, we present a detailed protocol of contact burn injury in the Yorkshire pig model with a focus on preoperative care, anesthesia, analgesia, wound excision and grafting, dressing application, and frequency of dressing changes.

Comparative wound healing--are the small animal veterinarian's clinical patients an improved translational model for human wound healing research?

Despite intensive research efforts into understanding the pathophysiology of both chronic wounds and scar formation, and the development of wound care strategies to target both healing extremes, problematic wounds in human health care remain a formidable challenge. Although valuable fundamental information regarding the pathophysiology of problematic wounds can be gained from in vitro investigations and in vivo studies performed in laboratory animal models, the lack of concordance with human pathophysiology has been cited as a major impediment to translational research in human wound care. Therefore, the identification of superior clinical models for both chronic wounds and scarring disorders should be a high priority for scientists who work in the field of human wound healing research. To be successful, translational wound healing research should function as an intellectual ecosystem in which information flows from basic science researchers using in vitro and in vivo models to clinicians and back again from the clinical investigators to the basic scientists. Integral to the efficiency of this process is the incorporation of models which can accurately predict clinical success. The aim of this review is to describe the potential advantages and limitations of using clinical companion animals (primarily dogs and cats) as translational models for cutaneous wound healing research by describing comparative aspects of wound healing in these species, common acute and chronic cutaneous wounds in clinical canine and feline patients, and the infrastructure that currently exists in veterinary medicine which may facilitate translational studies and simultaneously benefit both veterinary and human wound care patients.

Burn-induced increase in atrogin-1 and MuRF-1 in skeletal muscle is glucocorticoid independent but downregulated by IGF-I

The present study determined whether thermal injury increases the expression of the ubiquitin (Ub) E3 ligases referred to as muscle ring finger (MuRF)-1 and muscle atrophy F-box (MAFbx; aka atrogin-1), which are muscle specific and responsible for the increased protein breakdown observed in other catabolic conditions. After 48 h of burn injury (40% total body surface area full-thickness scald burn) gastrocnemius weight was reduced, and this change was associated with an increased mRNA abundance for atrogin-1 and MuRF-1 (3.1- to 8-fold, respectively). Similarly, burn increased polyUb mRNA content in the gastrocnemius twofold. In contrast, there was no burn-induced atrophy of the soleus and no significant change in atrogin-1, MuRF-1, or polyUb mRNA. Burns also did not alter E3 ligase expression in heart. Four hours after administration of the anabolic agent insulin-like growth factor (IGF)-I to burned rats, the mRNA content of atrogin-1 and polyUb in gastrocnemius had returned to control values and the elevation in MuRF-1 was reduced 50%. In contrast, leucine did not alter E3 ligase expression. In a separate study, in vivo administration of the proteasome inhibitor Velcade prevented burn-induced loss of muscle mass determined at 48 h. Finally, administration of the glucocorticoid receptor antagonist RU-486 did not prevent burn-induced atrophy of the gastrocnemius or the associated elevation in atrogin-1, MuRF-1, or polyUb. In summary, the acute muscle wasting accompanying thermal injury is associated with a glucocorticoid-independent increase in the expression of several Ub E3 ligases that can be downregulated by IGF-I.

Quantitative effects of thermal injury and insulin on the metabolism of the skeletal muscle using the perfused rat hindquarter preparation

Injury from a severe burn or trauma can propel the body into a hypermetabolic state that can lead to the significant erosion of lean muscle mass. Investigations describing this process have been somewhat limited due to the lack of adequate experimental models. Here we report the use of a perfused rat hindquarter preparation to study the consequences of a moderate burn injury (approximately 20% total body surface area), with or without the addition of exogenous insulin (12.5 mU/mL), on the fluxes of major metabolites across the isolated skeletal muscle. The metabolic flux data was further analyzed using metabolic flux analysis (MFA), which allows for the estimation of the impact of these conditions on the intracellular muscle metabolism. Results indicate that this model is able to capture the increased rate of proteolysis, glutamine formation, and the negative nitrogen balance associated with the burn-induced hypermetabolic state. The inclusion of exogenous insulin resulted in significant changes in several fluxes, including an increase in the metabolism of glucose and the flux through the pentose phosphate pathway, as well as a reduction in the metabolism of glutamine, alanine, and leucine. However, insulin administration did not affect the nitrogen balance or the rate of proteolysis in the muscle, as has been suggested using other techniques. The use of the perfused hindquarter model coupled with MFA is a physiologically relevant and experimentally flexible platform for the exploration of skeletal muscle metabolism under catabolic conditions, and it will be useful in quantifying the specific metabolic consequences of other therapeutic advances.

Thermal injury impairs cardiac protein synthesis and is associated with alterations in translation initiation

The purpose of the present study was to determine whether burn injury decreases myocardial protein synthesis and potential contributing mechanisms for this impairment. To address this aim, thermal injury was produced by a 40% total body surface area full-thickness scald burn in anesthetized rats, and the animals were studied 24 h late. Burn decreased the in vivo-determined rate of myocardial protein synthesis and translation efficiency by 25% but did not alter the protein synthetic rate in skeletal muscle. To identify potential mechanisms responsible for regulating mRNA translation in cardiac muscle, we examined several eukaryotic initiation factors (eIFs) and elongation factors (eEFs). Burn failed to alter eIF2B activity or the total amount or phosphorylation status of either eIF2 alpha or eIF2B epsilon in heart. In contrast, hearts from burned rats demonstrated 1) an increased binding of the translational repressor 4E-BP1 with eIF4E, 2) a decreased amount of eIF4E associated with eIF4G, and 3) a decreased amount of the hyperphosphorylated gamma-form of 4E-BP1. These changes in eIF4E availability were not seen in gastrocnemius muscle where burn injury did not decrease protein synthesis. Furthermore, constitutive phosphorylation of mTOR, S6K1, the ribosomal protein S6, and eIF4G were also decreased in hearts from burned rats. Burn did not appear to adversely affect elongation because there was no significant difference in the myocardial content of eEF1 alpha or eEF2 or the phosphorylation state of eEF2. The above-mentioned burn-induced changes in mRNA translation were associated with an impairment of in vitro myocardial performance. Finally, 24 h postburn, the cardiac mRNA content of IL-1 beta, IL-6, and high-mobility group protein B1 (but not TNF-alpha) was increased. In summary, these data suggest that thermal injury specifically decreases cardiac protein synthesis in part by decreasing mRNA translation efficiency resulting from an impairment in translation initiation associated with alterations in eIF4E availability and S6K1 activity.