Unburned Interspaces Research Articles

Copper Ion-Inspired Dual Controllable Drug Release Hydrogels for Wound Management: Driven by Hydrogen Bonds.

Bacterial infections and inflammation progression yield huge trouble for the management of serious skin wounds and burns. However, some hydrogel dressing exhibit poor wound-healing capabilities. Additionally, little information is given on the molecular theory of hydrogel gelation mechanisms and drug release performance from drug-polymer network in the water environment. Herein, cationic guar gum (CG) is first mixed with dipotassium glycyrrhizinate (DG), and then crosslinked Cu2+ to strengthen the mechanical strength followed by encapsulating mussel adhesive protein (MAP) as composite dressings. Intriguingly, CG-Cu2+ 0.5-DG10 possessed proper rheological properties and mechanical strength predominantly driven by strong CG-H2O-Cu2+ and Cu2+-CG hydrogen bonding interaction. Weak DG-CG hydrogen bonding only controlled DG release in the initial 4 h, while strong hydrogen bonding is the main force regulating the sustained release of Cu2+ within 48 h. The incorporation of MAP further loosened the tight crosslinking of CG-Cu2+ 0.5-DG10. The screened CG-Cu2+ 0.5-DG10/MAP possessed excellent self-healing, injectability, antibacterial, anti-inflammatory, cell proliferation-promotion activities with high biocompatibility. Therefore, CG-Cu2+ 0.5-DG10/MAP hydrogel expedited wound closure on S. aureus-infected full-thickness skin wound model and lowered necrosis progression to the unburned interspaces on a rat burn model. The results highlight the promising translational potential of Cu2+-inspired hydrogels for the management of burns and infected wounds.

Oral glutamine dipeptide or oral glutamine free amino acid reduces burned injury progression in rats.

This study was carried out to evaluate the effect of Glutamine, as a dipeptide or a free amino acid form, on the progression of burn injuries in rats. Thirty male Wistar rats were burned with a comb metal plate heated in boiling water (98 °C) for three minutes, creating four rectangular full-thickness burn areas separated by three unburned interspaces (zone of stasis) in both dorsum sides. The animals were randomized into three groups (n=10): saline solution (G1-Control) and treated groups that orally received Glutamine as dipeptide (G2-Dip) or free amino acid (G3-FreeAA). Two and seven days after burn injury, lesions were photographed for unburned interspaces necrosis evolution assessment. Seven days after injury, glutathione seric was measured and histopathological analysis was performed. By photographs, there was a significant reduction in necrosis progression in G3-Free-AA between days two and seven. Histopathological analysis at day 7 showed a significantly higher stasis zone without necrosis and a higher number of fibroblasts in G2-Dip and G3-FreeAA compared with G1-Control. Also, glutathione serum dosage was higher in G2-Dip. The plasmatic glutathione levels were higher in the G2-Dip than the G1-Control, and there was a trend to higher levels in G3-FreeAA. The reduction in histological lesions, greater production of fibroblasts, and greater amounts of glutathione may have benefited the evolution of burn necrosis, which showed greater preservation of interspaces.

75 Tranexamic Acid Reduces Burn Wound Conversion and Lung Inflammation in a Murine Comb Burn Model

Abstract Introduction Burn wound conversion is a process where superficial partial thickness burns convert into deep partial and even full thickness burn injuries. Unfortunately, the pathophysiology of this phenomenon is poorly understood. A therapeutic intervention that may prevent secondary progression and cell death in burn-injured tissue is desirable. Recent work by our group has established that tranexamic acid (TXA) has significant anti-inflammatory properties in addition to its well-known anti-fibrinolytic effects. This study investigates tranexamic acid as a novel therapeutic treatment to mitigate burn wound conversion and reduce systemic inflammation. Methods Sprague-Dawley rats were subjected to a hot comb burn contact injury using a 150-g brass comb preheated to 100°C, to create four rectangular burns, separated by three unburned interspaces. A subset of animals underwent the comb burn injury with an adjacent 30% TBSA contact injury using solid brass rods. The interspaces represent the ischemic zones simulating the zone of stasis. The treatment group received IP injection of TXA (100mg/kg) immediately after injury and once daily until sacrifice. Sham animals underwent an identical procedure, with application of a room temperature comb. Animals were sacrificed at 6hrs and 7-day time points post-injury. Photo images were obtained of the comb burn injury. Full-thickness biopsies from the ischemic zones and lung tissue were assessed with established histological and immunohistochemical (IHC) techniques. Results At 7-days post injury, the percentage of ischemic zones with necrosis was significantly reduced in the treatment group when compared with untreated burn controls by photographic image analysis. When compared with controls, the treatment groups had significantly less progression of ischemic zones to necrosis when assessed by standard microscopy. These findings were consistent in both the comb burn only and comb burn + 30%TBSA injury models. The TXA treatment group demonstrated significantly more expression of the regeneration marker (CTHRC-1) and a trend toward increased expression of the Ki-67 proliferation marker when compared to untreated burn group. At 6 hours post-injury, TXA significantly decreased infiltration of neutrophils in the lungs for the 30%TBSA burn injury model. Furthermore, systemic levels of mitochondrial DNA, IL-1α and TNFα were significantly lower in TXA treated animals when compared to untreated burn controls. Conclusions Animals treated with tranexamic acid demonstrated reduced burn wound conversion and decreased burn-induced SIRS response. Lung inflammation was also significantly reduced by administration of TXA after injury. Applicability of Research to Practice Tranexamic acid and agents with similar mechanisms of action may provide a treatment to reduce burn wound conversion. This therapy could be easily incorporated into standard acute burn care practices.

611 Progressing necrosis, how to make it stop? Clostridial collagenase debridement salvages the zone of stasis

IntroductionIn burns, conversion of partial thickness to deeper, full-thickness burns is largely attributed accumulation of chemical and mechanical mediators altering physiologic processes of tissue viability. Studies suggest that c. collagenase debridement digest denatured collagen without degrading otherwise intact collagen in granulation and healthy tissue. Moreover, modulating cellular responses to foster an anti-inflammatory milieu. To better understand c. collagenase effects in treatment of burns and salvaging the zone of stasis, we evaluated its ability to effectively debride while minimizing secondary necrosis for translative understanding associated with our clinical algorithmMethodsIn this prospective, controlled animal study, deep-partial thickness burns were created on the caudal dorsa. Following burn injuries, wounds were immediately cleaned and treated with either c. collagenase or a hydrogel. Daily treatment was provided. At selected time points, punch biopsies were obtained from unburned interspaces, fixed and prepared for evaluation. In tandem with pathological and histological assessment, samples were examined for cellular and analyte constituentsResultsGross images and histology revealed, c. collagenase treatment reduced necrosis and apoptosis. In control burns, papillary and reticular dermal collagen was shown to be disorganized and advancing in necrosis as exhibited by significant (p< 0.001) staining of HMGB1. In contrast, the interstices of c. collagenase treated burns demonstrated earlier sloughing of the epidermal layer with a clearly defined basement membrane and significantly (p< 0.001) reduced HMGB1 staining. Moreover, activated caspase 3a staining was significantly (p< 0.05) reduced in c. collagenase treated burn wounds. In assessing the inflammatory response, c. collagenase-treated wounds exhibited significantly (p< 0.05) greater neutrophil influx at day 1, with macrophage recruitment throughout days 1, 2, and 4. In further evaluation, macrophage polarization to MHC II and vascular network maintenance was significantly (p< 0.05) increased in c. collagenase treated woundsConclusionsThese data corroborate our clinical treatment algorithm, supported by presented case studies. Providing further evidence to potential cellular mechanisms to complement the clinical scenario. Thus, warranting inclusion of early treatment of c. collagenase debridement to preserve tissue from progressive necrosis

A Modified Burn Comb Model With a New Dorsal Frame That Allows for Local Treatment in Partial-Thickness Burns in Rats.

Burn wound progression (BWP) leads to vertical and horizontal injury extension. The "burn comb model" is commonly used, in which a full-thickness burn with intercalated unburned interspaces is induced. We aimed to establish an injury progressing to the intermediate dermis, allowing repeated wound evaluation. Furthermore, we present a new dorsal frame that enables topical drug application. Eight burn fields and six interspaces were induced on each of 17 rats' dorsa with a 10-second burn comb application. A developed 8-panel aluminum frame was sutured onto 12 animals and combined with an Elizabethan collar. Over 14 days, macroscopic and histologic wound assessment and laser speckle contrast imaging (LSCI) were performed besides evaluation of frame durability. The 10-second group was compared with nine animals injured with a full-thickness 60-second model. Frame durability was sufficient up to day 4 with 8 of the 12 frames (67%) still mounted. The 60-second burn led to an increased extent of interspace necrosis (P = .002). The extent of necrosis increased between days 1 and 2 (P = .001), following the 10-second burn (24% ± SEM 8% to 40% ± SEM 6%) and the 60-second burn (57% ± SEM 6% to 76% ± SEM 4%). Interspace LSCI perfusion was higher than burn field perfusion. It earlier reached baseline levels in the 10-second group (on day 1: 142% ± SEM 9% vs 60% ± SEM 5%; P &lt; .001). Within day 1, the 10-second burn showed histological progression to the intermediate dermis, both in interspaces and burn fields. This burn comb model with its newly developed fixed dorsal frame allows investigation of topical agents to treat BWP in partial-thickness burns.

Intradermal methylene blue administration on the progression of burn injuries.

A burn injury has two defined areas: central necrosis and an adjacent area of ischaemia, which may or may not progress to necrosis. The concentration of nitric oxide (NO) increases after burn injury and may originate from potent oxidising agents. Methylene blue (MB) may act as an antioxidant and is supposed to reduce burn progression. This investigation was carried out to evaluate the effects of intradermal MB on necrosis progression in burns. Full-thickness burn injuries were performed by applying a heated metal comb on the shaved back of male Wistar rats. The animals were divided into three groups: Control (C, n=7); MB (2mg/kg) one hour after burn injury (MB1h, n=11); and MB (2mg/kg) six hours after burn injury (MB6h, n=8). After seven days the lesions were photographed for visual assessment of burn necrosis; full-thickness cuts of lesions were dyed with Masson and Giemsa for microscopic histopathology; and tissue fragments of unburned interspaces were processed for chemiluminescence with nitrite/nitrate (NOX) and malondialdehyde (MDA) as oxidative stress markers. No statistically significant differences between groups were observed during visual analysis and NOX dosage. However, in microscopic analysis, the MB1h and MB6h groups showed smaller areas of necrosis, less inflammatory infiltration, and a more significant extension of interspaces. Furthermore, the dosage of MDA revealed that the MB1h group showed lower values when compared with the control group (p=0.001). The study provided good evidence that MB intradermal injection can reduce necrosis progression in ischaemic perilesional areas and suggests an alternative to treating burns.

Secondary Burn Progression Mitigated by an Adenosine 2A Receptor Agonist.

Current burn therapy is largely supportive with limited therapies to curb secondary burn progression. Adenosine 2A receptor (A2AR) agonists have anti-inflammatory effects with decreased inflammatory cell infiltrate and release of proinflammatory mediators. Using a porcine comb burn model, we examined whether A2AR agonists could mitigate burn progression. Eight full-thickness comb burns (four prongs with three spaces per comb) per pig were generated with the following specifications: temperature 115°C, 3-kg force, and 30-second application time. In a randomized fashion, animals (four per group) were then treated with A2AR agonist (ATL-1223, 3 ng/kg/min, intravenous infusion over 6 hours) or vehicle control. Necrotic interspace development was the primary outcome and additional histologic assessments were conducted. Analysis of unburned interspaces (72 per group) revealed that ATL-1223 treatment decreased the rate of necrotic interspace development over the first 4 days following injury (p < .05). Treatment significantly decreased dermal neutrophil infiltration at 48 hours following burn (14.63 ± 4.30 vs 29.71 ± 10.76 neutrophils/high-power field, p = .029). Additionally, ATL-1223 treatment was associated with fewer interspaces with evidence of microvascular thrombi through postburn day 4 (18.8% vs 56.3%, p = .002). Two weeks following insult, the depth of injury at distinct burn sites (adjacent to interspaces) was significantly reduced by ATL-1223 treatment (2.91 ± 0.47 vs 3.28 ± 0.58 mm, p = .038). This work demonstrates the ability of an A2AR agonist to mitigate burn progression through dampening local inflammatory processes. Extended dosing strategies may yield additional benefit and improve cosmetic outcome in those with severe injury.

Comparison of a topical surfactant and a topical antibiotic in the rat comb burn model

BackgroundBurn injury progression in the secondary zone of ischemia is common leading to delayed healing and increased scarring. We hypothesized that a topical surfactant, would reduce burn injury progression in a validated rat comb burn model compared with topical antibiotic ointment. MethodsWe created 40 comb burns on 20 rats which were randomized to daily topical application of the surfactant or a triple antibiotic ointment. The comb burns consisted of 4 full thickness burns with 3 unburned interspaces between the 4 burns. These unburned interspaces represented the zone of ischemia, and when left untreated, generally progress to full thickness necrosis within several days. Comb burns were assessed daily for the presence of gross necrosis of the interspaces. At 7 days the comb burns were excised and blindly evaluated for the presence of histological evidence of necrosis. The study had 80% power to detect a 25% difference in the percentages of necrotic interspaces on day 7. ResultsThere were no differences in the percentages of histologically necrotic interspaces at 7 days in burns treated with the surfactant or antibiotic ointment (85% [95%CI, 74 to 92] vs. 75% [95%CI, 63 to 84]; mean difference 10% [95%CI −4 to 24]). There were also no between group differences in the percentages of grossly necrotic interspaces on any of the seven days of the experiment. The surfactant remained intact and adherent while the antibiotic had been absorbed at each daily dressing change. ConclusionsA topical surfactant did not reduce injury progression in the rat comb burn model when compared with antibiotic ointment. The surfactant was more durable than the antibiotic ointment.

1EMF Oral Tadalafil Speeds Reepithelialization and Reduces Depth of Partial Thickness Porcine Burns

Burns, unlike mechanical wounds, are characterized by secondary injury progression due to reduced dermal microcirculation, inflammation, and oxidative stress. The vertical progression of injury delays healing or reepithelialization and increases scar formation. There are no current FDA-approved therapies to reduce burn injury vertical progression. Previous study in a rat comb model demonstrated that tadalafil, a phosphodiesterase 5 inhibitor used as a vasodilator to treat erectile dysfunction, reduces necrosis in the unburned interspaces compared with naproxen, NAC, or their combination.

Therapeutic efficacy of early photobiomodulation therapy on the zones of stasis in burns: An experimental rat model study.

This study aimed to investigate the role of photobiomodulation therapy in preventing zones of stasis in burn wounds. We hypothesized that photobiomodulation therapy could promote tissue formation and release of nitric oxide (NO), and reduce inflammatory responses, thereby dilating local microvessels, reducing necrosis and apoptosis. Thirty rats were randomly divided into control group (CG) and laser group (LG). The zone of stasis was formed by applying a brass comb to the skin resulting in four rectangular burns separated by three unburned interspaces. The left side was laser wound (LW), while the right side was shielded wound (SW). The LW of LG was immediately subjected to photobiomodulation therapy, followed by once-daily 30-minutes photobiomodulation therapy sessions. Skin ultrasound and Doppler angiography analyses were used to evaluate the statuses of the zones of stasis at 1, 24, and 96 hours after injury. Harvested burn wound tissue was subjected to hematoxylin-eosin staining and HMGB1, caspase 3, and thrombomodulin immunohistochemistry, and the contents of NO and TNF-α were measured in stasis tissue. Thrombomodulin, HMGB1, and caspase 3 immunohistochemistry revealed significantly lower positive staining rates in the LW of LG rats relative to the others at 96 hours (p < 0.05), as well as a significantly higher skin blood flow relative to the others (p < 0.05). The NO content was significantly higher in the LW of LG, compared with other wounds, at 24 and 96 hours after injury (p < 0.05). The TNF-α level was significantly lower in the LW of LG than in other wounds at 96 hours (p < 0.05). Early, local photobiomodulation therapy can effectively ameliorate injury progression in the zone of stasis. However, these beneficial effects are limited to the directly irradiated sites.

Effect of tadalafil on reduction of necrosis in the ischemic zone in a rat comb burn model

ObjectivesA major goal of burn management is to reduce the progression of necrosis in the zone of ischemia surrounding the central zone of necrosis. A rat comb burn model is often used to assess the progression of necrosis in the zone of ischemia. We compared various combinations of naproxen [NPX], N-acetyl cysteine [NAC], and tadalafil [TD] (a phosphodiesterase-5 inhibitor used as a vasodilator to treat erectile dysfunction) in a rat comb burn model to determine their effects on injury progression. MethodsWe created two comb burns on the backs of 40 anesthetized Sprague-Dawley rats using a brass comb with four rectangular prongs preheated in boiling water and applied for 30s, resulting in four rectangular 10×20mm full-thickness burns separated by three 5×20mm unburned interspaces, representing the ischemic zones. We randomized five animals each to daily oral gavage with TD (1mg/kg), NPX (10mg/kg), NAC (500mg/kg), NAC+NPX, TD+NPX, TD+NAC, TD+NPX+NAC, or normal saline [NS]. Wounds were observed daily for gross evidence of necrosis in the unburned interspaces and full-thickness biopsies from the interspaces were evaluated with Hematoxylin & Eosin seven days after injury for histological evidence of necrosis. ResultsThe percentages of interspaces with histological evidence of necrosis at day seven were TD-40%, NPX-93%, NAC-97%, NS-87%, TD+NPX-50%, TD+NAC-40%, TD+NPX+NAC-33%, and NPX+NAC-60% (P<0.001). Repeated measures ANOVA demonstrated reduced gross percentage of interspace area undergoing necrosis in all groups that included TD, compared with all groups not including TD (P<0.001). There were no differences among the various treatments within the groups that did or did not include TD. ConclusionsDaily oral therapy with tadalafil reduces necrosis in the unburned interspaces compared with naproxen, NAC, or their combination in a rat comb burn model. Addition of naproxen or NAC to tadalafil does not further reduce injury progression.

Resolvin D2 Limits Secondary Tissue Necrosis After Burn Wounds in Rats.

Secondary burn necrosis is the expansion and deepening of the original burn injury several days after injury. Limiting the extent of secondary burn necrosis may improve outcomes. In this study, we examined the ability of the lipid mediator of inflammation-resolution resolvin D2 (RvD2) and chromatin-lysing enzyme (DNase) to reduce secondary burn necrosis. Male Wistar rats were injured using a brass comb with 4 prongs heated in boiling water. This method created 2 parallel rows of 4 rectangular burned areas separated by 3 unburned interspaces. Starting at 2 hours after the burn injury, rats received either 25 ng/kg RvD2 intravenously daily for 7 days or 200 U/kg DNase every 12 hours for 3 days. We documented the necrosis around the initial wounds by digital photography. We used laser Doppler to assess the total blood flux in the burn area. We evaluated the functionality of the capillary network in the interspaces by optical coherence tomography angiography. We performed histological examination of wound skin tissue samples collected at 14 days postburn. We found that the interspace areas were preserved and had higher blood flow in the RvD2-treated group, while the burn areas expanded into the interspace areas, which were confluent by 7 days postburn, in the control-untreated group. We found a larger monocyte-to-neutrophil ratio in the RvD2-treated group compared with the DNase-treated and control groups (P < .05). Overall, RvD2 suppresses secondary necrosis and starts regeneration, highlighting the role of inflammation resolution as a potential therapeutic target in burn care.

Methylene blue reduces progression of burn and increases skin survival in an experimental rat model

Following burn, increased nitric oxide (NO) combine with superoxide anion forming peroxynitrite. Methylene blue (MB) has NO blocking and antioxidant effects. Male Wistar rats (250g) were burned bilaterally in dorsum with a comb metal plate heated inside boiling water and applied during 30s, creating four rectangular 10×20mm full-thickness burned areas separated by three 5×20mm unburned interspaces (stasis zone). 30 rats were randomized into three groups (n=10): treated groups received one dose of intraperitoneal (IP) MB injections (2mg/kg), one or six hours after injury, and control group received saline. Seven days after injury, wounds were visually analyzed for interspaces necrosis; full-thickness sections were evaluated with Masson staining; tissue fragments were processed for nitrite/nitrate (NOx) and malondialdehyde (MDA) dosages. Photographic analysis: interspaces progression to necrosis were higher in control (64.8%) than in one (44.7%) and six (13.3%) hours MB groups (P=0.0060). Histopathology showed lower necrosis percentage in one (34.85%) and six (41.62%) hours MB groups than control (77.03%) (P=0.0034) and higher normal skin percentage in one (25.33%) and six (26.85%) hours MB groups than control (8.32%) (P=0.0037). Re-epithelialization skin areas were higher in both MB groups (39.94% for one and 31.89% for six hours) than control (14.63%) (P=0.0210). Interspace’s NOx increased in both MB groups (P=0.0130) with no difference in burned areas. No MDA difference was observed. IP MB injection one or six hours after injury reduced necrosis progression in stasis area in the rat comb burn model suggesting an antioxidant effect reducing oxidative stress.

Topically applied metal chelator reduces thermal injury progression in a rat model of brass comb burn

Oxidative stress may be involved in the cellular damage and tissue destruction as burn wounds continues to progress after abatement of the initial insult. Since iron and calcium ions play key roles in oxidative stress, this study tested whether topical application of Livionex formulation (LF) lotion, that contains disodium EDTA as a metal chelator and methyl sulfonyl methane (MSM) as a permeability enhancer, would prevent or reduce burns. MethodsWe used an established brass comb burn model with some modifications. Topical application of LF lotion was started 5min post-burn, and repeated every 8h for 3 consecutive days. Rats were euthanized and skin harvested for histochemistry and immunohistochemistry. Formation of protein adducts of 4-hydroxynonenal (HNE), malonadialdehyde (MDA) and acrolein (ACR) and expression of aldehyde dehydrogenase (ALDH) isozymes, ALDH1 and ALDH2 were assessed. ResultsLF lotion-treated burn sites and interspaces showed mild morphological improvement compared to untreated burn sites. Furthermore, the lotion significantly decreased the immunostaining of lipid aldehyde–protein adducts including protein -HNE, -MDA and -ACR adducts, and restored the expression of aldehyde dehydrogenase isozymes in the unburned interspaces. ConclusionThis data, for the first time, demonstrates that a topically applied EDTA-containing lotion protects burns progression with a concomitant decrease in the accumulation of reactive lipid aldehydes and protection of aldehyde dehydrogenase isozymes. Present studies are suggestive of therapeutic intervention of burns by this novel lotion.

The Role of Necroptosis in Burn Injury Progression in a Rat Comb Burn Model.

Progression of cell death after burn injury may occur by one of three mechanisms: passive necrosis, apoptosis, and programmed necroptosis that requires the receptor-interacting protein kinase-3 (RIP-3). The hypothesis was that RIP-3 is present in normal and burned skin; that necroptosis plays a role in burn injury progression; and that treatment with necrostatin-1, an inhibitor of necroptosis, would reduce burn progression. Skin specimens from rats were examined for the presence of RIP-3. Using a 150-g brass comb preheated to 100°C, we created two comb burns (one on each side) consisting of four rectangular burns, separated by three unburned interspaces, on both sides of the backs of anesthetized male Sprague-Dawley rats (240 to 300 g). The interspaces represent the ischemic zones surrounding the central necrotic core. Left untreated, these areas undergo necrosis. In the first experiment, 10 rats each were randomized to 1.65 mg/kg necrostatin-1 or control given by intraperitoneal injection 1 hour after injury. In the second experiment, 10 rats each were randomized to two intravenous injections of 1.65 mg/kg necrostatin-1 or its vehicle at 1 and 4 hours after injury. The primary outcome was the percentage of interspaces undergoing necrosis within 7 days of injury. Binary data were compared with chi-square or Fishers' exact tests. All normal and burned skin specimens from rats stained positive for RIP-3. In the first experiment, nearly all unburned interspaces in both the experimental and the control rats underwent necrosis (47 of 48, 97.9% vs. 48 of 48, 100%; p = not significant [NS]). Similarly, in the second experiment, there was no difference in the percentage of unburned interspaces undergoing necrosis within 7 days of injury in rats treated with two doses of necrostatin-1 or the control vehicle (46 of 48, 95.8% vs. 48 of 48, 100%; p = NS). There were no wound infections noted in rats injected with necrostatin-1. The skin of rats contains RIP-3 necessary for necroptosis. Injection of rats with either a single intraperitoneal dose or two intravenous doses of necrostatin-1 failed to reduce burn injury progression in a rat comb burn model. This may be due to inactivity of necrostatin-1 or the lack of a role of necroptosis in burn injury progression in the rat comb burn model.

Short-Term Effects of Tree Removal on Infiltration, Runoff, and Erosion in Woodland-Encroached Sagebrush Steppe

Land owners and managers across the western United States are increasingly searching for methods to evaluate and mitigate the effects of woodland encroachment on sagebrush steppe ecosystems. We used small-plot scale (0.5 m2) rainfall simulations and measures of vegetation, ground cover, and soils to investigate woodland response to tree removal (prescribed fire and mastication) at two late-succession woodlands. We also evaluated the effects of burning on soil water repellency and effectiveness of aggregate stability indices to detect changes in erosion potential. Plots were located in interspaces between tree and shrub canopies and on undercanopy tree and shrub microsites. Erosion from untreated interspaces in the two woodlands differed more than 6-fold, and erosion responses to prescribed burning differed by woodland site. High-intensity rainfall (102 mm · h-1) on the less erodible woodland generated amplified runoff and erosion from tree microsites postfire, but erosion (45–75 g · m-2) was minor relative to the 3–13-fold fire-induced increase in erosion on tree microsites at the highly erodible site (240–295 g · m-2). Burning the highly erodible woodland also generated a 7-fold increase in erosion from shrub microsites (220–230 g · m-2) and 280–350 g · m-2 erosion from interspaces. High levels of runoff (40–45 mm) and soil erosion (230–275 g · m-2) on unburned interspaces at the more erodible site were reduced 4–5-fold (10 mm and 50 g · m-2) by masticated tree material. The results demonstrate that similarly degraded conditions at woodland-encroached sites may elicit differing hydrologic and erosion responses to treatment and that treatment decisions should consider inherent site-specific erodibility when evaluating tree-removal alternatives. Strong soil water repellency was detected from 0 cm to 3 cm soil depth underneath unburned tree canopies at both woodlands and its strength was not altered by burning. However, fire removal of litter exacerbated repellency effects on infiltration, runoff generation, and erosion. The aggregate stability index method detected differences in relative soil stability between areas underneath trees and in the intercanopy at both sites, but failed to provide any indication of between-site differences in erodibility or the effects of burning on soil erosion potential.

Indocyanine green dye angiography accurately predicts survival in the zone of ischemia in a burn comb model

IntroductionSurgical evaluation of burn depth is performed via clinical observation, with only moderate reliability. While perfusion analysis has been proposed to enhance accuracy, no perfusion study has attempted to predict burn extension into the area of ischemia surrounding the original insult. We examined whether laser Doppler imaging (LDI) and indocyanine green (ICG) angiography predicted survival in the zone of ischemia in a porcine hot comb burn model. MethodologySix full-thickness wounds were created on 5 female Yorkshire swine using a validated porcine hot comb burn model. 4 full-thickness burns were created separated by 3 unburned interspaces that represent the zone of ischemia. The interspaces between each comb burn were monitored using LDI and ICG Angiography at 1, 4, 24, and 48h after burn. Interspace survival was assessed via gross observation and blinded histological readings 7 days after injury. ResultsICG Angiographic assessments of burn perfusion were significantly different in viable vs. non-viable interspace perfusion at 1h, 4h, and 48h. Temporal plotting of a trend-line derived from quantitative perfusion measurements rendered two distinct graphs, allowing for the derivation of a predictive algorithm to separate viable and non-viable interspaces. LDI revealed no such prognostic trend. ConclusionResults from a validated porcine burn comb model suggest that ICG angiography has significant potential in the prediction of burn progression early after burn. However, the full potential of this technology cannot be determined until completion of clinical trials.

The Effects of Rat Mesenchymal Stem Cells on Injury Progression In a Rat Model

Burns are common injuries that can result in significant scarring, leading to poor function and disfigurement. Unlike mechanical injuries, burns often progress both in depth and in size over the first few days after injury, possibly due to inflammation and oxidative stress. A major gap in the field of burns is the lack of an effective therapy that reduces burn injury progression. Because stem cells have been shown to improve healing in several injury models, the authors hypothesized that species-specific mesenchymal stem cells (MSCs) would reduce injury progression in a rat comb-burn model. Using a brass comb preheated to 100°C, the authors created four rectangular burns, separated by three unburned interspaces on both sides of the backs of male Sprague-Dawley rats. The interspaces represented the ischemic zones surrounding the central necrotic core. In an attempt to reduce burn injury progression, 20 rats were randomized to tail vein injections of 1 mL of rat-specific MSCs, 10(6) cells/mL (n = 10), or normal saline (n = 10), 60 minutes after injury. While the authors were unable to identify any quantum dot (Q-dot)-labeled MSCs in the injured skin, at 7 days the mean percentage of the unburned interspaces that became necrotic in the MSC group was significantly less than in the control group (80% vs. 100%, p < 0.0001). Intravenous injection of rat MSCs reduced burn injury progression in a rat comb-burn model.

Immediate Burn Excision Fails to Reduce Injury Progression

The contact thermal injury model in the pig was used to determine whether immediate burn excision could alter the extent of injury progression. It was hypothesized that immediate excision of burns would prevent or reduce tissue necrosis in the uninjured interspaces. Four comb burns were created on the back of each animal, using a brass comb preheated in hot water (100 °C) for 5 minutes. This brass comb produced four distinctive burns sites separated by three "interspaces" of unburned skin, which were to undergo progressive injury. Immediately after burn creation, half of the full-thickness burns were excised leaving the unburned interspaces intact. Two full-thickness excisional wounds per pig with the dimensions identical to the comb burns were included as controls. Burn injury progression was microscopically assessed and reported as the percentage of unburned interspaces that progressed to full-thickness necrosis 7 days after injury. Scar formation was grossly evaluated on day 28 after injury and reported as the total surface area (in square centimeters) of the scar. A total of 24 combs with 72 interspaces were evenly distributed among the three groups. The unburned interspaces of both comb burns and excised comb burns had undergone progressive injury and were 100% dead (24/24; i.e., necrotic and/or apoptotic) 7 days postinjury (95% confidence interval, 86-100%) for both. However, interspaces of the control excisional wounds maintained complete viability, that is, no necrosis or apoptosis (0/24 [0%]; 95% confidence interval, 0-14%; P < .001). There was no significant difference in both surface area and depth of scar resulting from excised and nonexcised comb burns. Immediate burn excision neither prevented nor limited burn injury progression.

Curcumin Reduces Injury Progression in a Rat Comb Burn Model

The oriental spice curcumin has anti-inflammatory and antioxidant effects. When given orally before injury, curcumin reduces burn progression in a rat comb burn model. The authors hypothesized that intravenous administration of curcumin after injury would reduce burn progression and that its effects are mediated through iron chelation. Two comb burns were created on the dorsum of Sprague-Dawley rats (weight, 300 g) using a brass comb with four rectangular prongs preheated in boiling water and applied for 30 seconds resulting in four rectangular 10 × 20 mm full-thickness burns separated by three 5 × 20 mm unburned interspaces (zone of ischemia). Animals were randomized to receive one of four doses of crude curcumin or one of six doses of purified curcumin intravenously 1 and 24 hours after injury. Another set of animals were randomized to deferoxamine or control vehicle. Wounds were observed at 7 days after injury for visual evidence of necrosis in the unburned interspaces. Full-thickness biopsies from the interspaces were evaluated with Hematoxylin and Eosin staining 7 days after injury for evidence of necrosis. The percentage of unburned interspaces undergoing necrosis at 1 week by purified curcumin doses was 0 μg/kg, 74%; 0.3 μg/kg, 58%; 1 μg/kg, 53%; 3 μg/kg, 37%; 10 μg/kg, 63%; 30 μg/kg, 53%; and 100 μg/kg, 26%. The differences among the groups were significant (P = .03). When compared with controls, the 1 and 3 μg/kg curcumin treatment groups had significantly less progression of interspaces to necrosis (P = .04 and .002) as did the 30 and 100 μg/kg treatment groups (P = .03 and <.001). Deferoxamine did not reduce burn progression. When administered intravenously 1 and 24 hours after injury, both crude and purified curcumin reduce the percentage of unburned interspaces that undergo necrosis in a rat hot comb burn model. The effects of purified curcumin appear to be bimodal, suggesting more than one mechanism of action. The effects of curcumin do not appear to be mediated by iron chelation.