Inhibition of leukocyte adherence in a rabbit model of major thermal injury

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.

Blockade of IgM-Mediated Inflammation Alters Wound Progression in a Swine Model of Partial-Thickness Burn

In a mouse model, a second-degree burn elicits a severe inflammatory response that is mediated by circulating autoantibody specific for a neoantigen (nonmuscle myosin). Nonmuscle myosin is expressed by injured tissue, leading to amplified ulceration and scarring. We hypothesize that a synthetic peptide (N2) can mimic the neoantigen and competitively inhibit the autoantibody, decreasing inflammation, and reducing the extent of burn injury in a preclinical swine model of burn. Second-degree burns were created on young swine using brass cylinders, warmed to varying temperatures before skin contact. Animals were treated in double-blind fashion with normal saline, control peptide, or blocking peptide. Biopsies were taken at 2 hours, 1, 4, 7, and 14 days after burn injury. Burn wound healing parameters were assessed. Immunohistochemical staining for Ki-67, immunoglobulin (Ig)M, and interleukin (IL)-8 were also performed. N2 blocking peptide administration decreased dermal injury at 4 days with increased reepithelization, indicating more rapid healing. N2 normalized skin histology by 14 days and showed improved epidermal healing. Granulation tissue thickness was decreased, and there was an accompanying decrease in neutrophil infiltration. The basal layer of epidermis in N2-treated animals displayed more cells positive for Ki-67, suggesting a prompter regenerative capacity. Immunohistochemical staining demonstrated decreased deposition of immunoglobulin M and interleukin-8 after thermal injury in animals treated with N2 peptide, in comparison to controls. The findings of this study identify N2 blocking a specific inflammatory pathway, as a novel therapeutic approach, preventing the evolution of cutaneous burn injuries in a preclinical animal model.

Burn injury reduces neutrophil directional migration speed in microfluidic devices

Thermal injury triggers a fulminant inflammatory cascade that heralds shock, end-organ failure, and ultimately sepsis and death. Emerging evidence points to a critical role for the innate immune system, and several studies had documented concurrent impairment in neutrophil chemotaxis with these post-burn inflammatory changes. While a few studies suggest that a link between neutrophil motility and patient mortality might exist, so far, cumbersome assays have prohibited exploration of the prognostic and diagnostic significance of chemotaxis after burn injury. To address this need, we developed a microfluidic device that is simple to operate and allows for precise and robust measurements of chemotaxis speed and persistence characteristics at single-cell resolution. Using this assay, we established a reference set of migration speed values for neutrophils from healthy subjects. Comparisons with samples from burn patients revealed impaired directional migration speed starting as early as 24 hours after burn injury, reaching a minimum at 72–120 hours, correlated to the size of the burn injury and potentially serving as an early indicator for concurrent infections. Further characterization of neutrophil chemotaxis using this new assay may have important diagnostic implications not only for burn patients but also for patients afflicted by other diseases that compromise neutrophil functions.

Innate response to self-antigen significantly exacerbates burn wound depth

A major component of burn injury is caused by additional local damage from acute inflammation. Using a scald burn model in mice, we find that this part of the injury is dependent on recognition of self-antigen by specific natural IgM, leading to activation of the complement system. We propose that the depth of a burn wound is a sum of the thermal energy applied and of the degree of host inflammatory response.

A recombinant anti-ICAM-1 Fab fragment is as effective as the complete IgG antibody in treatment of burns in rabbits

The purpose of this study was to examine the efficiency of an Anti-ICAM-1-Fab fragment in the treatment of burns. Blocking ICAM-1 using murine IgG with the purpose to prevent further damage to the zone of stasis has proven its effectiveness in animal models as well as in humans. The use of murine Antibodies has some disadvantages including allergic reactions and complement activation. For the first time we examined an industry produced Fab-fragment blocking ICAM-1 and compared it to the corresponding IgG antibody. We showed in a standardised rabbit burn model that an Fab-fragment is capable of blocking ICAM-1 and therefore improving the reaction of the skin to trauma in the zone of stasis.

Semapimod Reduces the Depth of Injury Resulting in Enhanced Re-epithelialization of Partial-Thickness Burns in Swine

Studies suggest that tumor necrosis factor alpha (TNF-alpha) plays a role in burn pathogenesis. We conducted a randomized controlled experiment in swine to determine whether a novel macrophage inhibitor, semapimod (formerly known as CNI-1493), would blunt the local production of TNF-alpha, interleukin (IL)-1, and IL-6 in burns leading to less injury extension and faster re-epithelialization. After creating second-degree burns, animals received one or two intravenous boluses of semapimod 1 mg/kg or normal saline, and all burns were treated with silver sulfadiazine. The depth of follicular necrosis and thrombosis was reduced by either one or two doses of semapimod (P=.04 and .02, respectively). However, no differences were noted between groups in cytokine levels. Depth of scarring was similar in all groups. We conclude that Semapimod reduces the depth of follicular necrosis and thrombosis after second-degree burns in swine, indirectly resulting in more rapid re-epithelialization. However, this affect does not appear to be mediated by reduced local TNF-alpha, IL-1, or IL-6 protein levels.

Endothelial thrombomodulin (CD 141) in a rabbit burn model

Thrombomodulin (CD 141) is an endothelial surface transmembrane glycoprotein. It is involved in the activation of protein C in the inactivation of thrombin. In severe sepsis CD 141 is shed from the endothelial surface. This leads to disseminated intravascular coagulation (DIC), disturbed organ functions and multi organ failure (MOF). In this study, we investigated if endothelial bound thrombomodulin is shed in thermal injuries.

MATERIAL AND METHODS

In 10 New Zealand white rabbits full thickness and superficial partial thickness burns were produced. Dermal blood flow was analyzed by measuring the fluorescence of intravenously injected indocyanine green. Skin-biopsies were taken from the burn wounds from the zones of stasis between full thickness burns and from unburned skin 72 h post burn. Specimens were processed for immunoperoxidase staining using a specific monoclonal antibody against CD 141.

RESULTS

Dermal blood flow was reduced in burned skin areas and in the zones of stasis. Thrombomodulin was only detectable on the surface of capillary endothelial cells in specimens taken from unburned skin areas. No thrombomodulin was detectable in specimens taken from burn wounds or from the zones of stasis. Thus, shedding of thrombomodulin was detectable in areas with reduced dermal blood flow.

CONCLUSION

Thermal injuries affect the dermal endothelial surfaces resulting in a shedding of thrombomodulin. This mechanism might be involved in the development of progressive skin damage in the zone of stasis. Disseminated intravascular coagulation following inactivation of thrombomodulin might lead to multiple organ dysfunctions in severe burn injuries.

Clinical effects of inhibiting leukocyte adhesion with monoclonal antibody to intercellular adhesion molecule-1 (enlimomab) in the treatment of partial-thickness burn injury

BACKGROUND

A randomized, prospective, multicenter, double-blind, placebo-controlled, phase II clinical trial was performed to determine whether inhibition of leukocyte adherence by administration of monoclonal antibody directed against intercellular adhesion molecule-1 would improve burn wound healing.

METHODS

One hundred ten patients with burn injury ranging from 10% to 30% total body surface area were enrolled. Fifty-six patients received placebo (saline) and 54 patients received murine monoclonal antibody to the human intercellular adhesion molecule-1 (enlimomab). Treatment was initiated within 6 hours of injury. Patients had three distinct partial-thickness wound sites assessed. Laser Doppler flowmetry was used to stratify wounds on the day of injury. Wounds were assessed for healing status on day 21 postburn and categorized as healed, nonhealed, or grafted.

RESULTS

Patients treated with enlimomab had a significantly increased percentage of wounds that healed spontaneously in less than 21 days overall and when stratified by burn wound laser Doppler blood flow readings for those wounds at greatest risk for nonhealing.

CONCLUSION

These results support the concept that leukocyte adherence is involved in the pathogenesis of burn wound necrosis and suggest a therapeutic mechanism for modulating the inflammatory response after the burn injury that may improve wound healing.

Effect of thermal injury with Pseudomonas aeruginosa infection on pulmonary and systemic bacterial clearance

BACKGROUND

Despite improvements in burn wound care, infections, particularly pneumonia, remain a major hurdle to recovery from thermal injury. After burns, a variety of systemic immune and inflammatory changes contribute to the risk of infection. Clinically, infection coupled with burn injury seems to adversely affect susceptibility to subsequent infection.

METHODS

Using a mouse model of 10% total body surface area, full-thickness, third-degree burns with quantitative bacterial cultures of multiple tissues, the effect of graded intratracheal and intraperitoneal infections with Pseudomonas aeruginosa on the development of infection was assessed.

RESULTS

P. aeruginosa infection of blood and lung were demonstrated in burned mice 4 hours after they received 1 to 7.2x10(5) P. aeruginosa intratracheally but not in unburned control mice. Disseminated infection from endogenous bacterial species (Proteus, Enterococcus, Streptococcus) involving the lungs, liver, blood, and subeschar space was observed in mice that received both burns and infection with P. aeruginosa (intraperitoneally and intratracheally) but not with infection or burn alone (p<0.01). After burns, pulmonary bacterial clearance was delayed in association with both pulmonary infection (7.2x10(5) P. aeruginosa intratracheally) and intraperitoneal infection (10(7) P. aeruginosa intraperitoneally). Histologically, diffuse pneumonitis was observed in mice that received burns and infection but not in mice with either infection or burns alone.

CONCLUSION

Small thermal injuries coupled with transient infection of the lungs or peritoneum delay the clearance of bacteria from the lungs and contribute to infection of the lungs, liver, burn site, and blood by endogenous organisms. These studies support the synergy of relatively small thermal injuries with infectious exposures in the pathogenesis of pneumonia and systemic infections after burns.

A standard burn model using rats

Experimental burn models are always needed, being essential for burn research. In the present study, we describe a standard Fischer F-344 rat burn model, in which burns are produced with a heated brass bar. The animals were anesthetized with ketamine (90 mg/kg). After the burns, they were resuscitated with saline. Burns ranging from 26% to 30% of total body surface area resulted in a 62.5 % mortality rate after 25 days. This model is an additional option for those interested in burn research.

Role of L-selectin in physiological manifestations after burn and smoke inhalation injury in sheep

The effects of a monoclonal antibody against L-selectin [leukocyte adhesion molecule (LAM)1-3] on microvascular fluid flux were determined in conscious sheep subjected to a combined injury of 40% third-degree burn and smoke inhalation. This combined injury induced a rapid increase in systemic prefemoral lymph flow (sQlymph) from the burned area and a delayed-onset increase in lung lymph flow. The initial increase in sQlymph was associated with an elevation of the lymph-to-plasma oncotic pressure ratio; consequently, it leads to a predominant increase in the systemic soft tissue permeability index (sPI). In an untreated control group, the increased sPI was sustained beyond 24 h after injury. Pretreatment with LAM1-3 resulted in earlier recovery from the increased sPI, although the initial responses in sQlymph and sPI were identical to those in the nontreatment group. The delayed-onset lung permeability changes were significantly attenuated by pretreatment with LAM1-3. These findings indicate that both leukocyte-dependent and -independent mechanisms are involved in the pathogenesis that occurs after combined injury with burn and smoke inhalation.

Modulating the functions of neutrophils and lipid peroxidation by FK506 in a rat model of thermal injury

Neutrophils diffusely invade lung, liver, kidney, intestine, muscle and burned skin following burn injury. To ameliorate this invasion and minimize its effects, neutrophils can be modulated by giving neutrophil inhibitors and modulators. In this study, FK506 was used to decrease neutrophil infiltration and lipid peroxidation in remote organs (lung, liver, kidney and intestine) in a burned rat model. FK506 is a new major immunosuppressive agent that is known to modulate neutrophils during inflammation. Neutrophil infiltration was assessed indirectly by measuring myeloperoxidase (MPO) activity biochemically in remote organs following 30% full thickness burn injury. Malondialdehyde (MDA), the end product of lipid peroxidation, was measured biochemically in remote organs and plasma to determine if there is a relationship between neutrophil infiltration and lipid peroxidation after burn injury. FK506 was given intramuscularly at the dose of 0.5 and 1.0 mg/kg for three days before burn injury. Thermal trauma to the skin caused a statistically significant increase in MPO activity and MDA content in remote organs. FK506 was effective in reducing lipid peroxidation and neutrophil infiltration especially at 24 h postinjury in lung, liver and kidney. FK506 may have some benefit (prophylactic) in reducing systemic neutrophilic injury and related lipid peroxidation in burns.

Effects of allopurinol, ibuprofen and cyclosporin A on local microcirculatory disturbance due to burn injuries

This experiment was designed to study the reactions in the surrounding area of burn injury that may lead to further necrosis in 24 h. To prevent extension of burn size into the tissue adjacent to burn injury, it was attempted to reduce progressive microvascular damage by different drugs (ibuprofen, allopurinol or cyclosporin A (CyA)) in a rat model. The burn model consisted of a row of four 10 x 20 mm burn areas separated by three unburned 5 x 20 mm skin bridges (interspaces). To evaluate microcirculation and perfusion of panniculus carnosus muscle which is beneath the burned area of skin, the radioactive agent, technetium-99m methoxyisobutylisonitrile (99Tc01-MIBI) was used 24 h after the burn. Capillary permeability of injured tissue was assessed by the wet and dry weight technique. In all study groups, interspaces showed higher uptakes of 99Tc01-MIBI between 40 and 95 per cent, in comparison with burn sites in the first 24 h following burn. Among the treated rats better results were obtained by allopurinol and CyA treatment that commenced before burn than ibuprofen. Wet and dry ratios were found to be significantly lower in interspaces in rats pretreated with allopurinol and CyA. Results of this experiment showed that neutrophils and free radical-mediated injury may be involved in the pathogenesis of local response to thermal injury, and allopurinol and CyA have some effects to prevent progressive ischemia, capillary compromise and oedema.