Pulmonary changes in a mouse model of combined burn and smoke inhalation-induced injury

We investigated the pathophysiological alterations seen with combined burn and smoke inhalation injuries by focusing on pulmonary vascular permeability and cardiopulmonary function compared with those seen with either burn or smoke inhalation injury alone. To estimate the effect of factors other than injury, the experiments were also performed with no injury in the same experimental setting. Lung edema was most severe in the combined injury group. Our study revealed that burn injury does not affect protein leakage from the pulmonary microvasculature, even when burn is associated with smoke inhalation injury. The severity of lung edema seen with the combined injury is mainly due to augmentation of pulmonary microvascular permeability to fluid, not to protein. Cardiac dysfunction after the combined injury consisted of at least two phases. An initial depression was mostly related to hypovolemia due to burn injury. It was improved by a large amount of fluid resuscitation. The later phase, which was indicated to be a myocardial contractile dysfunction independent of the Starling equation, seemed to be correlated with smoke inhalation injury.

The Changes of Serum Amino Acids after Major Burn and Smoke Inhalation Injuries in Rats

Bronchial circulation plays a critical role in the pathophysiology of burn and smoke inhalation-induced acute lung injury. A 10-fold increase in bronchial blood flow is associated with excessive production of nitric oxide (NO) following smoke inhalation and cutaneous burn. Because an increased release of neuropeptides from the airway has been implicated in smoke inhalation injury, we hypothesized that direct delivery into the bronchial artery of low-dose 7-nitroindazole (7-NI), a specific neuronal NO synthase inhibitor, would attenuate smoke/burn-induced acute lung injury. Eighteen adult female sheep were instrumented for chronic hemodynamic monitoring 5 to 7 days before the injury. The bronchial artery was cannulated via intercostal thoracotomy, while blood flow was preserved. Acute lung injury was induced by 40% total body surface area third-degree cutaneous burn and smoke inhalation (48 breaths of cotton smoke, <40°C) under deep anesthesia. Following injury, animals (35.4 ± 1.1 kg) were divided into three groups: (a) 7-NI group: 1 h after injury, 7-NI (0.01 mg · kg · h, 2 mL · h) was continuously infused into the bronchial artery, n = 6; (b) control group: 1 h after injury, same amount of saline was injected into the bronchial artery, n = 6; (c) sham group: no injury, no treatment, same operation and anesthesia, n = 6. After injury, all animals were ventilated and fluid resuscitated according to an established protocol. The experiment was conducted for 24 h. Injury induced severe pulmonary dysfunction, which was associated with increases in lung edema formation, airway obstruction, malondialdehyde, and nitrate/nitrite. 7-Nitroindazole injection into the bronchial artery reduced the degree of lung edema formation and improved pulmonary gas exchange. The increase in malondialdehyde and nitrate/nitrite in lung tissue was attenuated by treatment. Our data strongly suggest that local airway production of NO contributes to pulmonary dysfunction following smoke inhalation and burn injury. Most mechanisms that drive this pathophysiology reside in the airway.

We compared the effect of a modest smoke inhalation injury, a burn injury alone, and a smoke inhalation injury plus a body burn, on the degree of lung oxidant-induced lipid peroxidation and lung injury. Prospective animal study with concurrent controls. An animal laboratory. Forty-four adult yearling female sheep (weight range 45 to 50 kg). Forty-four sheep were prepared with lung and prefemoral (soft tissue) lymph fistulas. Twelve breaths of cooled smoke with tidal volume of 10 mL/kg body weight were given to 24 sheep, producing a peak blood carboxyhemoglobin of 25% to 30%. Twelve sheep also received a 15% total body surface third-degree burn. Sheep were killed at 4 or 24 hrs. Circulating lipid peroxidation was monitored as conjugated dienes and tracheobronchial mucosal and lung parenchyma as malondialdehyde. Antioxidant defenses were monitored by catalase activity. Lung physiologic and histologic changes were compared. We noted intense airways inflammation in both smoke inhalation groups and lung parenchymal inflammation in all groups. Lung lymph flow was modestly increased (two-fold) in the smoke inhalation groups. Alveolar water content was not significantly increased after any injury. PaO2 was decreased at 24 hrs after the smoke insult alone. Parenchymal malondialdehyde content did not increase with the smoke insult alone, but did increase from a control value of 110 +/- 20 to 270 +/- 24 nmol/g tissue by 4 hrs in the combined burn and smoke injury group, while catalase activity decreased. Airway mucosal malondialdehyde did not increase in any group. We conclude that alveolar capillary permeability is not increased early after a moderate smoke injury or smoke injury with burn. Lipid peroxidation is not increased in large airway or lung parenchyma with early after-smoke exposure. The addition of a burn significantly increases lung parenchymal lipid peroxidation, but the oxidant changes do not correspond with the degree of early lung dysfunction.

One of the detrimental complications of burns is the onset of acute lung injury (ALI). In patients with extensive cutaneous burns in which the burned area exceeds 30% of the total body surface area, capillary hyperpermeability occurs not only at the injured site but also in regions distant from the initial insult [1, 2]. The vascular hyperpermeability leads to a large amount of fluid flux from the circulating plasma to the interstitial spaces. This lung edema formation is even more severe when the thermal injury is associated with smoke inhalation eventually leading to acute respiratory distress syndrome (ARDS) [3]. Previously, we designed an ovine model of combined burn and smoke inhalation injury and described the patho-physiology of ALI [3]. The ALI in combined burn and smoke inhalation injury is characterized by severe deterioration of pulmonary gas exchange (decrease in PaO2/FiO2, and increase in pulmonary shunt fraction), pulmonary microvascular leakage with subsequent formation of interstitial edema which is evidenced by increased pulmonary transvascular fluid flux (increased lung lymph flow), increased lung water content (lung wet-to-dry weight ratio), and increased pulmonary vascular permeability to both fluid and protein. These pathological changes are associated with severe pulmonary hypertension, massive airway obstruction by obstructive cast material, and increased ventilatory (peak and pause airway) pressures. In previous studies, we have also evaluated factors that play a crucial role in patho-genesis of ALI. There are several pathogenic factors, which affect the pulmonary function.

Burn-blast combined injury has a complex pathological process that may cause adverse complications and difficulties in treatment. This study aims to establish a standard animal model of severe burn-blast combined injury in rats and also to investigate early phasic changes of blood coagulation. By using 54 Wistar rats, distance from explosion source (Hexogen) and size of burned body surface area were determined to induce severe burn-blast combined injury. Thereafter, 256 rats were randomly divided into four groups (n = 64): blast injury group, burn injury group, burn-blast combined injury group, and sham injury group. Gross anatomy and pathological changes in lungs were investigated at 3, 24, 72, and 168 h, respectively. Blood was also collected for analyzing coagulation parameters as prothrombin time, activated partial thromboplastin time, and plasma levels of fibrinogen, D-dimer, antithrombin III, and α2-antiplasmin from 0 to 168 h after injury. Severe burn-blast combined injury was induced by inflicting rats with a moderate blast injury when placing rats 75 cm away from explosion source and a full-thickness burn injury of 25% total body surface area. The rats with burn-blast combined injury had more severe lung injuries when compared with the other three groups. Pathological examination in the BBL group showed diffused alveolar hemorrhage, fluid filling, alveolar atelectasis, rupture and hyperplasia of partial alveolar septum, emphysema-like change, reduced capillary bed, and infiltration of extensive polymorphonuclear cells after injury. The blood of combined injured rats was in a hypercoagulable state within 24 h, shortly restored from 24 to 48 h, and rehypercoagulated from 48 to 72 h after injury. A secondary excessively fibrinolytic function was also found thereafter. The rat model of burn-blast combined injury was successfully established by simulating real explosion characteristics. Rats with burn-blast combined injuries suffered from more severe lung injuries and abnormal coagulation and fibrinolytic function than those induced by a burn injury or a blast injury component. Hence, a time-dependent treatment strategy on coagulation function should be emphasized in clinical therapy of burn-blast combined injury.

Objective: To explore the effects of vitamin D3 on intestinal mucosal barrier of mice with severe burns. Methods: Forty-two C57BL/6C male mice aged eight to twelve weeks were divided into vitamin D3 vehicle+ sham injury group of seven mice, vitamin D3 vehicle+ burn injury group of fourteen mice, vitamin D3+ sham injury group of seven mice, and vitamin D3+ burn injury group of fourteen mice according to random number table. Mice in vitamin D3 vehicle+ sham injury group and vitamin D3 vehicle+ burn injury group were injected with vehicle of vitamin D3 at a dose of 0.1 mL intraperitoneally at 1, 24, and 48 h before burn experiment. Mice in vitamin D3+ sham injury group and vitamin D3+ burn injury group were injected with vitamin D3 at a dose of 100 ng/kg dissolved in 0.1 mL vehicle intraperitoneally at the same time points. Mice in vitamin D3 vehicle+ burn injury group and vitamin D3+ burn injury group were inflicted with 30% total body surface area full-thickness dermal scald (hereinafter referred to as burn) on the back by 98 ℃ hot water for 3 to 4 seconds. And mice in vitamin D3 vehicle+ sham injury group and vitamin D3+ sham injury were treated with 37 ℃ water on the back for 3 to 4 seconds to simulate injury. Seven mice in vitamin D3 vehicle+ sham injury group and seven mice in vitamin D3+ sham injury group at post injury hour (PIH) 24, and seven mice in vitamin D3 vehicle+ burn injury group and seven mice in vitamin D3+ burn injury group at PIH 6 and 24 were sacrificed respectively to collect mesentery lymph nodes, spleens, livers, and intestinal tissue. The mesentery lymph nodes, spleens, and livers of mice in each group were collected to observe growth of bacteria, and number of bacteria was counted. Intestinal tissue of mice in each group was collected to detect protein expressions of zonal occludin 1 (ZO-1) and occludin by immunohistochemistry staining method, distribution of ZO-1 by immunofluorescence staining method, and expression of occludin by Western blotting. Data were processed with Kruskal-Wallis H test, Nemenyi test, one-way analysis of variance, t test, and Bonferroni correction. Results: (1) At PIH 6 and 24, bacterial counts of mesentery lymph nodes, livers, and spleens of mice in vitamin D3 vehicle+ burn injury group were significantly higher than those of mice in vitamin D3 vehicle+ sham injury group (P<0.05). At PIH 6, bacterial counts of livers and spleens of mice in vitamin D3+ burn injury group were significantly lower than those of mice in vitamin D3 vehicle+ burn injury group (P<0.05). At PIH 24, bacterial counts of mesentery lymph nodes and livers of mice in vitamin D3+ burn injury group were significantly lower than those of mice in vitamin D3 vehicle+ burn injury group (P<0.05). (2) At PIH 6 and 24, expressions of ZO-1 and occludin of intestinal tissue of mice in vitamin D3 vehicle+ burn injury group were significantly lower than those of mice in vitamin D3 vehicle+ sham injury group, and expressions of ZO-1 and occludin of intestinal tissue of mice in vitamin D3+ burn injury group were close to those of mice in vitamin D3+ sham injury group. At PIH 6 and 24, expressions of ZO-1 and occludin of intestinal tissue of mice in vitamin D3+ burn injury group were significantly higher than those of mice in vitamin D3 vehicle+ burn injury group. (3) At PIH 6 and 24, compared with that of mice in vitamin D3 vehicle+ sham injury group, distribution of ZO-1 of intestinal mucosal epithelium of mice in vitamin D3 vehicle+ burn injury group was discontinuous. Distribution of ZO-1 of intestinal mucosal epithelium of mice in vitamin D3+ sham injury group was normal, and the distribution of ZO-1 of intestinal mucosal epithelium of mice in vitamin D3+ burn injury group was with good continuity. (4) At PIH 6 and 24, expressions of occludin of intestinal tissue of mice in vitamin D3 vehicle+ burn injury group were 0.720±0.003, 0.638±0.052 respectively, significantly lower than 0.918±0.003 of mice in vitamin D3 vehicle+ sham injury group (t=57.33, 5.36, P<0.05). At PIH 6 and 24, expressions of occludin of intestinal tissue of mice in vitamin D3+ burn injury group were 0.994±0.058, 1.064±0.060, close to 0.938±0.023 of mice in vitamin D3+ sham injury group (t=0.91, 1.96, P>0.05). At PIH 6 and 24, expressions of occludin of intestinal tissue of mice in vitamin D3 vehicle+ burn injury group were significantly lower than those of mice in vitamin D3+ burn injury group (t=4.75, 5.35, P<0.05). Conclusions: Intestinal bacterial translocation can occur in the early stage of severe burn. And vitamin D3 plays a protective role in the intestinal mucosal barrier post severe burn to reduce the bacterial translocation by protecting tight junction proteins of intestinal epithelium.

Inhalation injury contributes to the morbidity and mortality of burn victims. In humans and in an ovine model of combined smoke inhalation and burn injury, bronchospasm and acute airway obstruction contribute to progressive pulmonary insufficiency. This study tests the hypothesis that muscarinic receptor antagonist therapy with tiotropium bromide, an M1 and M3 muscarinic receptor antagonist, will decrease the airway constrictive response and acute bronchial obstruction to improve pulmonary function compared to injured animals without treatment. Randomized, prospective study involving 32 sheep. Large-animal intensive care research laboratory. The study consisted of six groups: a sham group (n=4, instrumented noninjured), a control group (n=6, injured and not treated), and tiotropium bromide-treated groups, including both preinjury and postinjury nebulization protocols. Treatments for these groups included nebulization with 36 μg of tiotropium bromide 1 hr before injury (n=6) and postinjury nebulization protocols of 18 μg (n=6), 36 μg (n=6), and 72 μg (n=4) administered 1 hr after injury. All treated groups received an additional 14.4 μg every 4 hrs for the 24-hr study period. Pretreatment with tiotropium bromide significantly attenuated the increases in ventilatory pressures, pulmonary dysfunction, and upper airway obstruction that occur after combined smoke inhalation and burn injury. Postinjury treatments with tiotropium bromide were as effective as pretreatment in preventing pulmonary insufficiency, although a trend toward decreased obstruction was present only in all post-treatment conditions. There was no improvement noted in pulmonary function in animals that received a higher dose of tiotropium bromide. This study describes a contribution of acetylcholine to the airway constrictive and lumenal obstructive response after inhalation injury and identifies low-dose nebulization of tiotropium bromide as a potentially efficacious therapy for burn patients with severe inhalation injury.

Development of a long-term ovine model of cutaneous burn and smoke inhalation injury and the effects of early excision and skin autografting

Reactive nitrogen species such as peroxynitrite play a significant role in burn and smoke inhalation injury. The bronchial circulation increases more than 10-fold in response to this combination injury. We hypothesized that direct delivery of low-dose WW-85, a peroxynitrite decomposition catalyst, into the bronchial artery would attenuate burn- and smoke inhalation-induced acute lung injury. In adult female sheep (n = 17), the bronchial artery was cannulated in preparation surgery. After a 5- to 7-day recovery period, sheep were subjected to a burn (40% total body surface area, third degree) and inhalation injury (48 breaths of cotton smoke, <40°C). The animals were divided into three groups following the injury: (i) WW-85 group: 1 h after injury, WW-85 (0.002 mg/kg per hour) was continuously infused into the bronchial artery, n = 5; (ii) control group: 1 h after injury, an equivalent amount of saline was injected into the bronchial artery, n = 6; (iii) sham group: no injury, no treatment, same operation and anesthesia, n = 6. All animals were mechanically ventilated and fluid resuscitated equally. In the control group, the injury induced a severe deterioration of pulmonary oxygenation and shunting and an increase in pulmonary microvascular permeability toward sham. The injury was further associated with an increase in reactive nitrogen species in lung tissues of the control group. All these alterations were significantly attenuated in the WW-85 group. We demonstrated that a low dosage of WW-85 directly administered into the bronchial artery attenuated pulmonary dysfunction to the same extent as higher systemically administered doses in previous experiments. Our data strongly suggest that local airway production of peroxynitrite contributes to pulmonary dysfunction following smoke inhalation and burn injury.

To elucidate the effects of low-dose arginine vasopressin on cardiopulmonary functions and nitrosative stress using an established model of acute lung injury. Prospective, randomized, controlled laboratory experiment. Investigational intensive care unit. Eighteen chronically instrumented sheep. Sheep were randomly assigned to a sham group without injury or treatment, an injury group without treatment (40% total body surface area third-degree burn and 48 breaths of cold cotton smoke), or an injured group treated with arginine vasopressin (0.02 IU·min⁻¹) from 1 hr after injury until the end of the 24-hr study period (each n = 6). All sheep were mechanically ventilated and fluid resuscitated using an established protocol. There were no differences among groups at baseline. The injury was characterized by a severe deterioration of cardiopulmonary function (left ventricular stroke work indexes and Pao2/Fio2 ratio; p < .01 each vs. sham). Compared with controls, arginine vasopressin infusion improved myocardial function, as suggested by higher stroke volume indexes and left ventricular stroke work indexes (18-24 hrs and 6-24 hrs, respectively; p < .05 each). In addition to an improved gas exchange (higher Pao2/Fio2 ratios from 6 to 24 hrs, p < .01 each), pulmonary edema (bloodless wet-to-dry-weight ratio; p = .018), bronchial obstruction (p = .01), and pulmonary shunt fraction (12-24 hrs; p ≤ .001 each) were attenuated in arginine vasopressin-treated animals compared with controls. These changes occurred along with reduced nitrosative stress, as indicated by lower plasma levels of nitrate/nitrite (12-24 hrs, p < .01 each), as well as lower myocardial and pulmonary tissue concentrations of 3-nitrotyrosine (p = .041 and p = .042 vs. controls, respectively). At 24 hrs, pulmonary 3-nitrotyrosine concentrations were negatively correlated with Pao2/Fio2 ratio (r = -.882; p < .001) and myocardial 3-nitrotyrosine content with stroke volume indexes (r = -.701; p = .004). Low-dose arginine vasopressin reduced nitrosative stress and improved cardiopulmonary functions in sheep with acute lung injury secondary to combined burn and smoke inhalation injury.

Acute effects of combined burn and smoke inhalation injury on carboxyhemoglobin formation, tissue oxygenation, and cardiac performance

Introduction Despite recent advancements in burn wound management, individuals afflicted with severe burn injuries face heightened susceptibility to opportunistic infections, largely attributed to a hyper pro-inflammatory response followed by a chronic compensatory anti-inflammatory response. Our prior research has identified 1) Nuclear Factor-Erythroid-2-Related Factor (NRF2) as a critical immunomodulatory component, that when activated, induces protective anti-inflammatory pathways after injury, and 2) Mammalian Target of Rapamycin (mTOR) that, when inhibited, reduces pro-inflammatory responses. However, therapeutic use of these targets is limited, as known modulators of these pathways are insoluble in saline and require long-term application. We hypothesized that administering NRF2 agonist (CDDO) in addition to Rapamycin encapsulated in soluble Poly (lactic-co-glycolic acid) (PLGA) microparticles (MP) will reduce the acute hyper-inflammatory response following a burn injury. Methods To assess this, we conducted in vivo experiments using our murine model of burn and smoke inhalation (BI) injury. We utilized female C57BL/6 mice and separated them into four groups (n=6 per group): (1) Sham, (2) BI, (3) BI+CDDO, and (4) BI+CDDO+Rapamycin MP (combo-MP). An hour after the burn, the mice were resuscitated, and MP administered IP. After 48 hours, we collected and isolated total splenic and lung tissue mRNA and analyzed immune gene expression using nanoString. Results We found significant changes in the activation patterns of immune genes and their associated pathways. For example, in mice administered with CDDO-MP, splenic tissue displayed a significant reduction (p &amp;lt; 0.05) in the activation of inflammatory genes when compared to untreated BI, such as CASP1 gene and CD9. Mice treated with combo-MP had a significant reduction in inflammatory genes associated with mTOR pathway, such as CCL9 and C3 when compared to those only treated with CDDO-MP. To examine the molecular pathways influenced by the drugs, we conducted an Ingenuity Pathway Analysis (IPA). The IPA confirmed the significantly (p-value &amp;lt; 0.05) increased anti-inflammatory signaling by downregulation of Pathogen Induced Cytokine Storm Signaling when compared to CDDO mice Conclusions Our findings strongly suggest that the multi-modal MP-based therapy holds considerable promise in reprogramming the immune response after burn injuries, particularly by mitigating the hyper-inflammatory phase. Applicability of Research to Practice This research identifies targets that are likely applicable to therapeutic targeting to reduce patient morbidity and mortality after burn and combined injuries.

Combined radiation and burn injuries are likely to occur after nuclear events, such as a meltdown accident at a nuclear energy plant or a nuclear attack. Little is known about the mechanisms by which combined injuries result in higher mortality than by either insult alone, and few animal models exist for combined radiation and burn injury. Herein, the authors developed a murine model of radiation and scald burn injury. Mice were given a single dose of 0, 2, 4, 5, 6, or 9 Gray (Gy) alone, followed by a 15% TBSA scald burn. All mice receiving ≤4 Gy of radiation with burn survived combined injury. Higher doses of radiation (5, 6, and 9 Gy) followed by scald injury had a dose-dependent increase in mortality (34, 67, and 100%, respectively). Five Gy was determined to be the ideal dose to use in conjunction with burn injury for this model. There was a decrease in circulating white blood cells in burn, irradiated, and combined injury (5 Gy and burn) mice by 48 hours postinjury compared with sham (49.7, 11.6, and 57.3%, respectively). Circulating interleukin-6 and tumor necrosis factor-α were increased in combined injury at 48 hours postinjury compared with all other treatment groups. Prolonged overproduction of proinflammatory cytokines could contribute to subsequent organ damage. Decreased leukocytes might exacerbate immune impairment and susceptibility to infections. Future studies will determine whether there are long lasting consequences of this early proinflammatory response and extended decrease in leukocytes.

IntroductionSevere burn injury leads to many systemic stresses that can seriously impact multiple systems throughout the body. These stresses are further exacerbated if there is a combined burn and inhalation injury, which leads to increased morbidity and mortality for many patients. Combined burn and inhalation injury causes an intense systemic inflammatory response and activation of the innate immune system which can lead to inflammatory complications, such as systemic inflammatory response syndrome and multiple organ failure. Nuclear Factor-Erythroid-2-Related Factor (NRF2) is a transcription factor that acts to downregulate overt damaging pro-inflammatory and oxidative responses and maintain immune homeostasis. This transcription factor remains bound to Kelch-like ECH-associated protein 1 (KEAP1) in the cytoplasm. Under oxidative stress, NRF2 dissociates from KEAP1 and translocates to the nucleus where it facilitates the transcription of anti-inflammatory and antioxidant genes. We hypothesized that NRF2 is a key regulator after burn and inhalation injury, and activation of NRF2 can limit the severity of burn and inhalation injury.MethodsTo test this, we have developed a mouse model of combined cutaneous burn and woodsmoke inhalation injury. After burn and inhalation injury, we found that NRF2-/- knockout mice have higher mortality compared to wild-type (WT) mice and suffer from increased vascular permeability and lung edema, suggesting that this transcription factor is important for controlling morbidity and mortality. In WT mice, NRF2 is activated following burn and inhalation injury, however, based on immunohistochemical staining, it is not sufficiently induced following this insult since it remains in the cytoplasm and is unable to transcribe anti-inflammatory genes. Therefore, we treated WT mice with an intraperitoneal injection of bardoxolone-methyl microparticles, a NRF2 activator that separates KEAP1 from NRF2 in the cytoplasm, immediately after burn and inhalation injury in WT miceResultsWe observed significant decreases in mortality as well as reduced concentrations of certain pro-inflammatory cytokines in the blood and bronchoalveolar-lavage fluid of these mice. In the lungs of these mice, there was an upregulation in numerous pathways involved in the management of inflammation and immune response compared to mice that did not receive bardoxolone-methyl microparticles.ConclusionsIn conclusion, treatment with bardoxolone-methyl microparticles immediately after burn and inhalation injury might be effective for reducing the severity of the inflammatory response and limiting inflammatory complications.