The dynamics of the early inflammatory response in double-hit burn and sepsis animal models

Kinetics of Inflammatory Mediators in the Immune Response to Burn Injury: Systematic Review and Meta-Analysis of Animal Studies

Burns are often accompanied by a dysfunctional immune response, which can lead to systemic inflammation, shock, and excessive scarring. The objective of this study was to provide insight into inflammatory pathways associated with burn-related complications. Because detailed information on the various inflammatory mediators is scattered over individual studies, we systematically reviewed animal experimental data for all reported inflammatory mediators. Meta-analyses of 352 studies revealed a strong increase in cytokines, chemokines, and growth factors, particularly 19 mediators in blood and 12 in burn tissue. Temporal kinetics showed long-lasting surges of proinflammatory cytokines in blood and burn tissue. Significant time-dependent effects were seen for IL-1β, IL-6, TGF-β1, and CCL2. The response of anti-inflammatory mediators was limited. Burn technique had a profound impact on systemic response levels. Large burn size and scalds further increased systemic, but not local inflammation. Animal characteristics greatly affected inflammation, for example, IL-1β, IL-6, and TNF-α levels were highest in young, male rats. Time-dependent effects and dissimilarities in response demonstrate the importance of appropriate study design. Collectively, this review presents a general overview of the burn-induced immune response exposing inflammatory pathways that could be targeted through immunotherapy for burn patients and provides guidance for experimental set-ups to advance burn research.

Acute and Chronic Molecular Signatures and Associated Symptoms of Blast Exposure in Military Breachers

Injuries from exposure to explosions rose dramatically during the Iraq and Afghanistan wars, which motivated investigations of blast-related neurotrauma and operational breaching. In this study, military “breachers” were exposed to controlled, low-level blast during a 10-day explosive breaching course. Using an omics approach, we assessed epigenetic, transcriptional, and inflammatory profile changes in blood from operational breaching trainees, with varying levels of lifetime blast exposure, along with daily self-reported symptoms (with tinnitus, headaches, and sleep disturbances as the most frequently reported). Although acute exposure to blast did not confer epigenetic changes, specifically in DNA methylation, differentially methylated regions (DMRs) with coordinated gene expression changes associated with lifetime cumulative blast exposures were identified. The accumulative effect of blast showed increased methylation of PAX8 antisense transcript with coordinated repression of gene expression, which has been associated with sleep disturbance. DNA methylation analyses conducted in conjunction with reported symptoms of tinnitus in the low versus high blast incidents groups identified DMRS in KCNE1 and CYP2E1 genes. KCNE1 and CYP2E1 showed the expected inverse correlation between DNA methylation and gene expression, which have been previously implicated in noise-related hearing loss. Although no significant transcriptional changes were observed in samples obtained at the onset of the training course relative to chronic cumulative blast, we identified a large number of transcriptional perturbations acutely pre- versus post-blast exposure. Acutely, 67 robustly differentially expressed genes (fold change ≥1.5), including UFC1 and YOD1 ubiquitin-related proteins, were identified. Inflammatory analyses of cytokines and chemokines revealed dysregulation of MCP-1, GCSF, HGF, MCSF, and RANTES acutely after blast exposure. These data show the importance of an omics approach, revealing that transcriptional and inflammatory biomarkers capture acute low-level blast overpressure exposure, whereas DNA methylation marks encapsulate chronic long-term symptoms.

Endogenous Uteroglobin as Intrinsic Anti-inflammatory Signal Modulates Monocyte and Macrophage Subsets Distribution Upon Sepsis Induced Lung Injury

Sepsis is a serious clinical condition which can cause life-threatening organ dysfunction, and has limited therapeutic options. The paradigm of limiting excessive inflammation and promoting anti-inflammatory responses is a simplified concept. Yet, the absence of intrinsic anti-inflammatory signaling at the early stage of an infection can lead to an exaggerated activation of immune cells, including monocytes and macrophages. There is emerging evidence that endogenous molecules control those mechanisms. Here we aimed to identify and describe the dynamic changes in monocyte and macrophage subsets and lung damage in CL57BL/6N mice undergoing blunt chest trauma with subsequent cecal ligation and puncture. We showed that early an increase in systemic and activated Ly6C⁺CD11b⁺CD45⁺Ly6G^- monocytes was paralleled by their increased emigration into lungs. The ratio of pro-inflammatory Ly6C^highCD11b⁺CD45⁺Ly6G^- to patrolling Ly6C^lowCD11b⁺CD45⁺Ly6G^- monocytes significantly increased in blood, lungs and bronchoalveolar lavage fluid (BALF) suggesting an early transition to inflammatory phenotypes during early sepsis development. Similar to monocytes, the level of pro-inflammatory Ly6C^highCD45⁺F4/80⁺ macrophages increased in lungs and BALF, while tissue repairing Ly6C^lowCD45⁺F4/80⁺ macrophages declined in BALF. Levels of inflammatory mediators TNF-α and MCP-1 in blood and RAGE in lungs and BALF were elevated, and besides their boosting of inflammation via the recruitment of cells, they may promote monocyte and macrophage polarization, respectively, toward the pro-inflammatory phenotype. Neutralization of uteroglobin increased pro-inflammatory cytokine levels, activation of inflammatory phenotypes and their recruitment to lungs; concurrent with increased pulmonary damage in septic mice. In in vitro experiments, the influence of uteroglobin on monocyte functions including migratory behavior, TGF-β1 expression, cytotoxicity and viability were proven. These results highlight an important role of endogenous uteroglobin as intrinsic anti-inflammatory signal upon sepsis-induced early lung injury, which modules the early monocyte/macrophages driven inflammation.

Short Summary

Blunt chest injury is the third largest cause of death following major trauma, and ongoing excessive pro-inflammatory immune response entails high risk for the development of secondary complications, such as sepsis, with limited therapeutic options. In murine double hit trauma consisting of thoracic trauma and subsequent cecal ligation and puncture, we investigated the cytokine profile, pulmonary epithelial integrity and phenotypic shift of patrolling Ly6C^lowCD11b⁺CD45⁺Ly6G^- monocytes and Ly6C^lowCD45⁺F4/80⁺ macrophages to pro-inflammatory Ly6C^highCD11b⁺CD45⁺Ly6G^- monocytes and Ly6C^highCD45⁺F4/80⁺ cells in blood, lungs and bronchoalveolar lavage fluid (BALF). Pro-inflammatory mediators and phenotypes were elevated and uteroglobin neutralization led to further increase. Enhanced total protein levels in BALF suggests leakage of respiratory epithelium. In vitro, uteroglobin inhibited the migratory capacity of monocytes and the TGF-β1 expression without affecting the viability. These results highlight an important role of endogenous uteroglobin as an intrinsic anti-inflammatory signal upon sepsis-induced early lung injury, which modulates the early monocyte/macrophages driven inflammation.

Real-time dynamics of neutrophil clustering in response to phototoxicity-induced cell death and tissue damage in mouse ear dermis

Neutrophils are highly motile innate immune cells; they actively migrate in response to inflammatory signals. Using two-photon intravital microscopy, we discovered that neutrophils form stable clusters upon phototoxicity at a certain threshold. Without significant damage to the collagen structure of mouse dermis, neutrophils aggregated together with nearby neutrophils. Surprisingly, this in situ neutrophil clustering resulted in rigorous changes of migratory direction. The density of residing neutrophils was also a critical factor affecting clustering. Additionally, we found that the triggering point of neutrophil aggregation was correlated with the structure of the extracellular matrix in the ear dermis, where autofluorescence was strongly observed. This swarming behavior of neutrophils may reflect an unknown communication mechanism of neutrophils during migration under sterile injury.

To Treat or Not to Treat: The Effects of Pain on Experimental Parameters

A common dilemma faced by all animal bioethics committees arises when exceptions are proposed to the use of analgesics in painful procedures. The committee and researcher must weigh the possible confounding effects of including additional drugs (analgesics) in their treatment regimen against the moral obligation to perform humane research. Often neglected in these considerations are the potential confounding effects of unrelieved pain and consistency with pain-relieving practices in human medicine. In this review, we summarize what is currently known regarding the molecular and physiologic effects of pain and analgesics in common animal models used across several therapeutic areas. This work is intended to help provide guidance and assurance that a comprehensive approach has been taken when contemplating how pain relief will be applied in animal research protocols.

The protective effects of bone marrow-derived mesenchymal stem cell (BMSC) on LPS-induced acute lung injury via TLR3-mediated IFNs, MAPK and NF-κB signaling pathways

The study attempted to clarify the protective role of bone marrow-derived mesenchymal stem cell (BMSC) transplantation on LPS-induced acute lung injury (ALI) of rats. BMSC were obtained from bone marrow of rat, cultured and proliferated in vitro. Rats of ALI were established through lipopolysaccharide (LPS) administration. Male rats were allocated to control group, ALI group and BMSC, transplantation group. Rats were sacrificed after BMSC injection after 12h, 24h and 48h. Here we investigated the role of BMSC in LPS-induced alveolar macrophages to further demonstrate the mechanism of BMSC to lung injury. TLR3, a member of Toll-like receptor family, has been found in macrophages and the cell surface. In our study, first BMSC successfully reversed LPS-induced lung injury by hematoxylin-eosin (H&E) staining, ameliorated apoptosis via TUNEL and flow cytometer analysis, as well as improved cell structure. And then, western blot, quantitative real-time PCR, immunohistochemistry and immunofluorescence analysis were used to confirm that TLR3 was significantly down-regulated for BMSC treatment. Subsequently, TRIF and RIP1, down-streaming signals of TLR3, were inhibited greatly, leading to TRAF3, MAPK as well as NF-κB inactivity. Our results indicated that BMSC transplantation group displayed inhibitory effects on interferon (IFNs) levels via TLR3 in LPS-induced ALI and preventive effects on inflammation response via TLR3-regualted MAPK and NF-κB signaling pathway in LPS-induced lung injury. The present study indicated that BMSC could display protective effects on LPS-induced ALI and provide an experimental basis for clinical therapy.

ROS-Mediated NLRP3 Inflammasome Activity Is Essential for Burn-Induced Acute Lung Injury

The NLRP3 inflammasome is necessary for initiating acute sterile inflammation. However, its role in the pathogenesis of burn-induced acute lung injury (ALI) is unknown. This study aimed to determine the role of the NLRP3 inflammasome and the signaling pathways involved in burn-induced ALI. We observed that the rat lungs exhibited enhanced inflammasome activity after burn, as evidenced by increased levels of NLRP3 expression and Caspase-1 activity and augmented inflammatory cytokines. Inhibition of NLRP3 inflammasome by BAY11-7082 attenuated burn-induced ALI, as demonstrated by the concomitant remission of histopathologic changes and the reduction of myeloperoxidase (MPO) activity, inflammatory cytokines in rat lung tissue, and protein concentrations in the bronchoalveolar lavage fluid (BALF). In the in vitro experiments, we used AMs (alveolar macrophages) challenged with burn serum to mimic the postburn microenvironment and noted that the serum significantly upregulated NLRP3 inflammasome signaling and reactive oxygen species (ROS) production. The use of ROS scavenger N-acetylcysteine (NAC) partially reversed NLRP3 inflammasome activity in cells exposed to burn serum. These results indicate that the NLRP3 inflammasome plays an essential role in burn-induced ALI and that burn-induced NLRP3 inflammasome activity is a partly ROS-dependent process. Targeting this axis may represent a promising therapeutic strategy for the treatment of burn-induced ALI.

ROS-Mediated NLRP3 Inflammasome Activity Is Essential for Burn-Induced Acute Lung Injury

The NLRP3 inflammasome is necessary for initiating acute sterile inflammation. However, its role in the pathogenesis of burn-induced acute lung injury (ALI) is unknown. This study aimed to determine the role of the NLRP3 inflammasome and the signaling pathways involved in burn-induced ALI. We observed that the rat lungs exhibited enhanced inflammasome activity after burn, as evidenced by increased levels of NLRP3 expression and Caspase-1 activity and augmented inflammatory cytokines. Inhibition of NLRP3 inflammasome by BAY11-7082 attenuated burn-induced ALI, as demonstrated by the concomitant remission of histopathologic changes and the reduction of myeloperoxidase (MPO) activity, inflammatory cytokines in rat lung tissue, and protein concentrations in the bronchoalveolar lavage fluid (BALF). In the in vitro experiments, we used AMs (alveolar macrophages) challenged with burn serum to mimic the postburn microenvironment and noted that the serum significantly upregulated NLRP3 inflammasome signaling and reactive oxygen species (ROS) production. The use of ROS scavenger N-acetylcysteine (NAC) partially reversed NLRP3 inflammasome activity in cells exposed to burn serum. These results indicate that the NLRP3 inflammasome plays an essential role in burn-induced ALI and that burn-induced NLRP3 inflammasome activity is a partly ROS-dependent process. Targeting this axis may represent a promising therapeutic strategy for the treatment of burn-induced ALI.

ROS-Mediated NLRP3 Inflammasome Activity Is Essential for Burn-Induced Acute Lung Injury

The NLRP3 inflammasome is necessary for initiating acute sterile inflammation. However, its role in the pathogenesis of burn-induced acute lung injury (ALI) is unknown. This study aimed to determine the role of the NLRP3 inflammasome and the signaling pathways involved in burn-induced ALI. We observed that the rat lungs exhibited enhanced inflammasome activity after burn, as evidenced by increased levels of NLRP3 expression and Caspase-1 activity and augmented inflammatory cytokines. Inhibition of NLRP3 inflammasome by BAY11-7082 attenuated burn-induced ALI, as demonstrated by the concomitant remission of histopathologic changes and the reduction of myeloperoxidase (MPO) activity, inflammatory cytokines in rat lung tissue, and protein concentrations in the bronchoalveolar lavage fluid (BALF). In the in vitro experiments, we used AMs (alveolar macrophages) challenged with burn serum to mimic the postburn microenvironment and noted that the serum significantly upregulated NLRP3 inflammasome signaling and reactive oxygen species (ROS) production. The use of ROS scavenger N-acetylcysteine (NAC) partially reversed NLRP3 inflammasome activity in cells exposed to burn serum. These results indicate that the NLRP3 inflammasome plays an essential role in burn-induced ALI and that burn-induced NLRP3 inflammasome activity is a partly ROS-dependent process. Targeting this axis may represent a promising therapeutic strategy for the treatment of burn-induced ALI.

Dynamics of hepatic gene expression and serum cytokine profiles in single and double-hit burn and sepsis animal models

We simulate the pathophysiology of severe burn trauma and burn-induced sepsis, using rat models of experimental burn injury and cecal ligation and puncture (CLP) either individually (singe-hit model) or in combination (double-hit model). The experimental burn injury simulates a systemic but sterile pro-inflammatory response, while the CLP simulates the effect of polymicrobial sepsis. Given the liver׳s central role in mediating the host immune response and onset of hypermetabolism after burn injury, elucidating the alterations in hepatic gene expression in response to injury can lead to a better understanding of the regulation of the inflammatory response, whereas circulating cytokine protein expression, reflects key systemic inflammatory mediators. In this article, we present both the hepatic gene expression and circulating cytokine/chemokine protein expression data for the above-mentioned experimental model to gain insights into the temporal dynamics of the inflammatory and hypermetabolic response following burn and septic injury. This data article supports results discussed in research articles (Yang et al., 2012 [1,4]; Mattick et al. 2012, 2013 [2,3]; Nguyen et al., 2014 [5]; Orman et al., 2011, 2012 [6–8]).

Systemic inflammatory responses and multiple organ dysfunction syndrome following skin burn wound and Pseudomonas aeruginosa infection in mice

Burn wound-related sepsis is associated with the development of systemic inflammatory response syndrome and multiple organ dysfunction syndrome (MODS). This study is aimed at investigating the development and progression of SIS and MODS in a mouse model of skin burn sepsis. C57BL/6J mice were randomly divided into the sham, burn, Pseudomonas, and burn/Pseudomonas groups. The back skin of the sham, burn, and burn/Pseudomonas groups was burned about 10% of total area with using 37°C or 98°C water for 8 s, respectively, followed by inoculating with Pseudomonas aeruginosa. The Pseudomonas group was infected with P. aeruginosa without burn injury. Their body weights, mortality, organ histology, and function as well as systemic inflammation were measured longitudinally. The burn/Pseudomonas mice lost more body weights than did mice from the other groups and had a significantly higher mortality rate (P < 0.05). The burn/Pseudomonas mice exhibited significantly higher levels of bacterial loads in different organs and serum endotoxin, interleukin 1β, interleukin 6, tumor necrosis factor α, and C-reactive protein than those in mice from the other groups (P < 0.05). The burn/Pseudomonas mice also displayed more severe liver, lung, and kidney tissue damage and impaired organ functions, particularly at 72 h after inoculation than did the burn and Pseudomonas groups of mice. Our data indicate that burn and P. aeruginosa infection induced severe sepsis and rapidly progressed into systemic inflammatory response syndrome and MODS in mice.

Severe sepsis facilitates intestinal colonization by extended-spectrum-β-lactamase-producing Klebsiella pneumoniae and transfer of the SHV-18 resistance gene to Escherichia coli during antimicrobial treatment

Infections caused by multidrug-resistant pathogens are frequent and life threatening in critically ill patients. To investigate whether severe sepsis affects gut colonization by resistant pathogens and genetic exchange between opportunistic pathogens, we tested the intestinal-colonization ability of an extended-spectrum beta-lactamase-producing Klebsiella pneumoniae strain carrying the SHV-18 resistance gene and the transfer ability of the resistance gene to endogenous Escherichia coli under ceftriaxone treatment in rats with burn injury only or severe sepsis induced by burns plus endotoxin exposure. Without ceftriaxone treatment, the K. pneumoniae strain colonized the intestine in both septic and burned rats for a short time, with clearance occurring earlier in burn-only rats but never in sham burn rats. In both burned and septic rats, the colonization level of the challenge strain dropped at the beginning and then later increased during ceftriaxone treatment, after which it declined gradually. This pattern coincided with the change in resistance of K. pneumoniae to ceftriaxone during and after ceftriaxone treatment. Compared with burn-only injury, severe sepsis had a more significant effect on the change in antimicrobial resistance to ceftriaxone. Only in septic rats was the resistance gene successfully transferred from the challenge strain to endogenous E. coli during ceftriaxone treatment; the gene persisted for at least 4 weeks after ceftriaxone treatment. We concluded that severe sepsis can facilitate intestinal colonization by an exogenous resistant pathogen and the transfer of the resistance gene to a potential endogenous pathogen during antimicrobial treatment.

Combined radiation and burn injury results in exaggerated early pulmonary inflammation

Events such as a nuclear meltdown accident or nuclear attack have potential for severe radiation injuries. Radiation injury frequently occurs in combination with other forms of trauma, most often burns. Thus far, combined injury studies have focused mainly on skin wound healing and damage to the gut. Since both radiation exposure and remote burn have pulmonary consequences, we examined the early effects of combined injury on the lung. C57BL/6 male mice were irradiated with 5 Gy of total body irradiation followed by a 15% total body surface area scald burn. Lungs from surviving animals were examined for evidence of inflammation and pneumonitis. At 48 h post-injury, pathology of the lungs from combined injury mice showed greater inflammation compared to all other treatment groups, with marked red blood cell and leukocyte congestion of the pulmonary vasculature. There was excessive leukocyte accumulation, primarily neutrophils, in the vasculature and interstitium, with occasional cells in the alveolar space. At 24 and 48 h post-injury, myeloperoxidase levels in lungs of combined injury mice were elevated compared to all other treatment groups (P < 0.01), confirming histological evidence of neutrophil accumulation. Pulmonary levels of the neutrophil chemoattractant KC (CXCL1) were 3 times above that of either injury alone (P < 0.05). Further, monocyte chemotactic protein-1 (MCP-1, CCL2) was increased two- and threefold compared to burn injury or radiation injury, respectively (P < 0.05). Together, these data suggest that combined radiation and burn injury augments early pulmonary congestion and inflammation. Currently, countermeasures for this unique type of injury are extremely limited. Further research is needed to elucidate the mechanisms behind the synergistic effects of combined injury in order to develop appropriate treatments.

Two-hit model of brain damage in the very preterm newborn: small for gestational age and postnatal systemic inflammation

BACKGROUND

We sought to disentangle the contributions of perinatal systemic inflammation and being small for gestational age (SGA) to the occurrence of low Bayley Mental Development Indices (MDIs) at the age of 2 y.

METHODS

We measured the concentration of 25 inflammation-related proteins in blood obtained during the first two postnatal weeks from 805 infants who were born before the 28th wk of gestation and who had MDI measurements at the age of 2 y and were able to walk independently.

RESULTS

SGA newborns who did not have systemic inflammation (a concentration of an inflammation-related protein in the top quartile for gestational age on two days a week apart) were at a greater risk of an MDI <55, but not 55-69, than their peers who had neither SGA nor systemic inflammation. SGA infants who had elevated blood concentrations of interleukin (IL)-1β, tumor necrosis factor-α, or IL-8 during the first 2 postnatal weeks were at even higher risk of an MDI <55 than their SGA peers without systemic inflammation and their non-SGA peers with systemic inflammation.

CONCLUSION

SGA appears to place very preterm newborns at an increased risk of a very low MDI. Systemic inflammation adds considerably to the increased risk.

Why the term neonatal encephalopathy should be preferred over neonatal hypoxic-ischemic encephalopathy

The unresponsiveness of the full-term newborn is sometimes attributed to asphyxia, even when no severe physiologic disturbance occurred during labor and delivery. The controversy about whether to use the name "hypoxic-ischemic encephalopathy" or "newborn encephalopathy" has recently flared in publications directed toward pediatricians and neurologists. In this clinic opinion piece, I discuss the importance to obstetricians of this decision and explain why "newborn encephalopathy" should be the default term.

Stoichiometry based steady-state hepatic flux analysis: computational and experimental aspects

: The liver has many complex physiological functions, including lipid, protein and carbohydrate metabolism, as well as bile and urea production. It detoxifies toxic substances and medicinal products. It also plays a key role in the onset and maintenance of abnormal metabolic patterns associated with various disease states, such as burns, infections and major traumas. Liver cells have been commonly used in in vitro experiments to elucidate the toxic effects of drugs and metabolic changes caused by aberrant metabolic conditions, and to improve the functions of existing systems, such as bioartificial liver. More recently, isolated liver perfusion systems have been increasingly used to characterize intrinsic metabolic changes in the liver caused by various perturbations, including systemic injury, hepatotoxin exposure and warm ischemia. Metabolic engineering tools have been widely applied to these systems to identify metabolic flux distributions using metabolic flux analysis or flux balance analysis and to characterize the topology of the networks using metabolic pathway analysis. In this context, hepatic metabolic models, together with experimental methodologies where hepatocytes or perfused livers are mainly investigated, are described in detail in this review. The challenges and opportunities are also discussed extensively.

Long-term dynamic profiling of inflammatory mediators in double-hit burn and sepsis animal models

Burn injuries together with its subsequent complications, mainly bacterial infections originating from gastrointestinal tract, activate the host immune system through stimulation of a series of local and systemic responses, including the release of inflammatory mediators. To gain a more comprehensive understanding of these complex physiological changes and to propose therapeutic approaches to combat the deleterious consequences of burn and septic shocks, it is essential to analyze animal models of burn and sepsis. In this study, we analyzed the long term profiles of cytokines and chemokines in rat models which received burn injury followed 2 days later by cecal ligation and puncture (CLP) to induce sepsis and were sacrificed at different time points within 10 days (0, 1, 2, 3, 4, 7 and 10 days). It was observed that MCP-1 concentrations were elevated in all animal models following the burn injury or CLP treatment. IP-10 concentration was persistently decreased after CLP or sham-CLP treatments. GRO/KC concentration was also increased following the burn injury and CLP. It was elucidated that, in more severe injury model which received both burn and CLP treatments, GMCSF and MIP-1α (chemokines), IL-1α (a pro-inflammatory cytokine) and IL-6 (exhibiting both pro- and anti-inflammatory behaviors) were upregulated on the 7th and 10th days, which might be to protect the host system from the subsequent complications caused by burn and sepsis. In order to elucidate critical regulatory interactions, putative transcription factors of the inflammatory mediators which have been significantly changed following the injuries were further identified by analyzing the conserved regions of the promoters of cytokines and chemokines. In conclusion, the long term profiles of the inflammatory mediators were profoundly characterized in this study to gain a comprehensive understanding of inflammatory mediators' behaviors in various injury models.