Burn injury-induced alterations in wound inflammation and healing are associated with suppressed hypoxia inducible factor-1alpha expression

The Complexity of the Post-Burn Immune Response: An Overview of the Associated Local and Systemic Complications

Burn injury induces a complex inflammatory response, both locally and systemically, and is not yet completely unravelled and understood. In order to enable the development of accurate treatment options, it is of paramount importance to fully understand post-burn immunology. Research in the last decades describes insights into the prolonged and excessive inflammatory response that could exist after both severe and milder burn trauma and that this response differs from that of none-burn acute trauma. Persistent activity of complement, acute phase proteins and pro- and anti-inflammatory mediators, changes in lymphocyte activity, activation of the stress response and infiltration of immune cells have all been related to post-burn local and systemic pathology. This "narrative" review explores the current state of knowledge, focusing on both the local and systemic immunology post-burn, and further questions how it is linked to the clinical outcome. Moreover, it illustrates the complexity of post-burn immunology and the existing gaps in knowledge on underlying mechanisms of burn pathology.

Inflammatory response: The target for treating hyperpigmentation during the repair of a burn wound

Hyperpigmentation is a common complication in patients with burn injuries during wound healing; however, the mechanisms underlying its occurrence and development remain unclear. Recently, postinflammatory hyperpigmentation (PIH) was found to result from overproduction of melanin. Local or systemic inflammatory responses are often observed in patients who develop hyperpigmentation. However, we lack studies on the relationship between PIH and burn injury. Therefore, we comprehensively reviewed the existing literature on the melanogenesis of the skin, inflammatory mechanisms in pigmentation, and local or systemic alteration in inflammatory cytokines in patients suffering from burn trauma to elucidate the relationship between PIH and burn injury. We believe that this review will guide further research on regulating melanin production in the burn management process.

AB569, a non-toxic combination of acidified nitrite and EDTA, is effective at killing the notorious Iraq/Afghanistan combat wound pathogens, multi-drug resistant Acinetobacter baumannii and Acinetobacter spp

Multi-drug resistant (MDR) Acinetobacter baumannii (Ab) and Acinetobacter spp. present monumental global health challenges. These organisms represent model Gram-negative pathogens with known antibiotic resistance and biofilm-forming properties. Herein, a novel, nontoxic biocide, AB569, consisting of acidified nitrite (A-NO₂^-) and ethylenediaminetetraacetic acid (EDTA), demonstrated bactericidal activity against all Ab and Acinetobacter spp. strains, respectively. Average fractional inhibitory concentrations (FICs) of 0.25 mM EDTA plus 4 mM A-NO₂^- were observed across several clinical reference and multiple combat wound isolates from the Iraq/Afghanistan wars. Importantly, toxicity testing on human dermal fibroblasts (HDFa) revealed an upper toxicity limit of 3 mM EDTA plus 64 mM A-NO₂^-, and thus are in the therapeutic range for effective Ab and Acinetobacter spp. treatment. Following treatment of Ab strain ATCC 19606 with AB569, quantitative PCR analysis of selected genes products to be responsive to AB569 revealed up-regulation of iron regulated genes involved in siderophore production, siderophore biosynthesis non-ribosomal peptide synthetase module (SBNRPSM), and siderophore biosynthesis protein monooxygenase (SBPM) when compared to untreated organisms. Taken together, treating Ab infections with AB569 at inhibitory concentrations reveals the potential clinical application of preventing Ab from gaining an early growth advantage during infection followed by extensive bactericidal activity upon subsequent exposures.

Effective administration of cranial drilling therapy in the treatment of fourth degree temporal, facial and upper limb burns at high altitude: A case report

BACKGROUND

Fourth degree burns damage the full thickness of the skin and affect underlying tissues. Skin grafting after debridement is often used to cover the wounds of salvageable severe burns. A granulation wound can be formed by drilling the skull to the barrier layer to solve the problem of skull exposure. Low oxygen levels present at high altitudes aggravate ischemia and hypoxia which can negatively impact wound healing. The impaired healing in such cases can be ameliorated by hyperbaric oxygen therapy.

CASE SUMMARY

We describe a patient who presented with fourth degree burns to the left temporal and facial regions upon admission in December 2018. The periosteum of the skull and the deep fascia of the face were exposed. After the first stage of debridement and skin grafting, the temporal skin did not survive well. Granulation was induced by cranial drilling, and then a local flap was transferred to cover the wound. The left temporal and facial wounds were completely covered and the patient recovered well.

CONCLUSION

Skin grafting and flap transfer after early debridement to cover the wound and control infection were of great significance. In the later stages of the patient’s treatment, survival of the skin graft and skin flap was observed. The second stage repair was performed to achieve successful skin grafting by cranial granulation. Granulation was formed by drilling the skull, and then the wound was closed, which is suitable for cases with skull exposure and wounds with poor blood supply. We consider that hyperbaric oxygen treatment and improving tissue oxygen supply were beneficial in this patient.

Recombinant Treponema pallidum protein Tp0136 promotes fibroblast migration by modulating MCP-1/CCR2 through TLR4

BACKGROUND

Chancre self-healing is an important clinical feature in the early stages of syphilis infection. Wound healing may involve an important mechanism by the migration of fibroblasts filling the injured lesion. However, the specific mechanism underlying this process is still unknown.

OBJECTIVES

We aimed to analyse the role of Tp0136 in the migration of fibroblasts and the related mechanism.

METHODS

The migration ability of fibroblasts was detected by a wound-healing assay. RT-PCR and ELISA detected the expression of MCP-1, IL-6 and MMP-9. TLR4 expression was detected by RT-PCR. The protein levels of CCR2 and relevant signalling pathway molecules were measured by Western blotting.

RESULTS

Tp0136 significantly promoted fibroblast migration. Subsequently, the levels of MCP-1 and its receptor CCR2 were increased in this process. The migration of fibroblasts was significantly inhibited by an anti-MCP-1 neutralizing antibody or CCR2 inhibitors. Furthermore, studies demonstrated that Tp0136 could activate the ERK/JNK/PI3K/NF-κB signalling pathways through TLR4 activity and that signalling pathways inhibitors could weaken MCP-1 secretion and fibroblast migration.

CONCLUSIONS

These findings demonstrate that Tp0136 promotes the migration of fibroblasts by inducing MCP-1/CCR2 expression through signalling involving the TLR4, ERK, JNK, PI3K and NF-κB signalling pathways, which could contribute to the mechanism of chancre self-healing in syphilis.

Topical Insulin Modulates Inflammatory and Proliferative Phases of Burn-Wound Healing in Diabetes-Induced Rats

The healing time of burn wounds depends on surface area and depth of the burn and associated comorbidities. Diabetes mellitus (DM) causes delays in the healing process by extending the inflammatory phase. Treatment with topical insulin can improve the inflammatory phase, restore metabolic dysregulation, and modulate impaired cellular signaling in burn wounds. The objective of this study was to evaluate markers of the inflammatory and proliferative phases of second-degree burns after topical insulin treatment in diabetic rats. Type I DM was induced with streptozotocin in male Wistar rats. The animals' backs were shaved and subjected to thermal burning. Rats were randomized into two groups: control diabetic (DC) and insulin diabetic (DI). At Days 7 and 14 postburn, rats were euthanized, and wound-tissue sections were evaluated by hematoxylin and eosin, Weigert, and Verhöeff staining, immunohistochemistry-paraffin, and enzyme-linked immunosorbent assay. A significant increase in reepithelialization was seen on Days 7 and 14 in DI versus DC rats. On Day 7, interleukin (IL)-1β, IL-6, monocyte chemotactic protein (MCP)-1, and F4/80 expression were increased in DI versus DC rats. On Day 14, MCP-1 expression was decreased and F4/80 increased in DI versus DC rats. On Days 7 and 14, Ki-67, transforming growth factor-β1, vascular endothelial growth factor expression, and formation of elastic fibers were increased in DI versus DC rats. Topical insulin modulates burn-wound healing in diabetic animals by balancing inflammation and promoting angiogenesis and formation of elastic fibers.

The Dynamics of the Skin's Immune System

The skin is a complex organ that has devised numerous strategies, such as physical, chemical, and microbiological barriers, to protect the host from external insults. In addition, the skin contains an intricate network of immune cells resident to the tissue, crucial for host defense as well as tissue homeostasis. In the event of an insult, the skin-resident immune cells are crucial not only for prevention of infection but also for tissue reconstruction. Deregulation of immune responses often leads to impaired healing and poor tissue restoration and function. In this review, we will discuss the defensive components of the skin and focus on the function of skin-resident immune cells in homeostasis and their role in wound healing.

Protective effect of a hydrogen sulfide donor on balloon injury-induced restenosis via the Nrf2/HIF-1α signaling pathway

Restenosis is liable to occur following treatment with endovascular interventional therapy. Increasing evidence indicates that hydrogen sulfide (H₂S) exhibits numerous physiological properties, including antioxidative and cardioprotective disease properties. Thus, the present study aimed to investigate the anti-restenosis effects of H₂S and its protective mechanisms. A balloon dilatation restenosis model was used, in which model Sprague-Dawley rats were treated with sodium hydrosulfide (NaHS: A donor of H₂S, 30 µmol/kg) by intraperitoneal injection for 4 weeks. Histological observations of the carotid artery were performed, and H₂S production and the expression of Nuclear factor-E2-related factor 2 (Nrf2)/hypoxia-inducible factor (HIF)-1α signaling pathway proteins were measured. In addition, human umbilical vein endothelial cells (HUVECs) were treated with NaHS following the inhibition of Nrf2 or HIF-1α expression. The expression of Nrf2/HIF-1α signaling pathway proteins, tube formation and cell migration were evaluated thereafter. The results demonstrated that NaHS treatment significantly increased H₂S production in rats with restenosis, and that neointimal thickness decreased significantly in arteries with restenosis. Furthermore, an increase in H₂S production enhanced the nuclear accumulation of Nrf2 and expression of its downstream targets, heme oxygenase-1 and superoxide dismutase, as well as HIF-1α. Similar effects of NaHS on the expression of these proteins were observed in HUVECs. Additionally, these findings indicated that NaHS-induced HIF-1α expression was dependent on Nrf2 expression. NaHS treatment also markedly increased tube formation by upregulating vascular endothelial growth factor expression and cell migration, both of which were mediated by the Nrf2/HIF-1α signaling pathway, and suppressed the migration and proliferation of human vascular smooth muscle cells. Thus, NaHS-mediated H₂S production was observed to prevent neointimal hyperplasia, promote activation of the Nrf2/HIF-1α signal pathway, and enhance HUVEC tube formation and migration, thereby exerting protective effects on balloon injury-induced restenosis.

Restoration of skin pigmentation after deep partial or full-thickness burn injury

Significant skin pigmentation changes occur when patients suffer deep burn injuries. These pigmentation disorders may cause not only cosmetic and psychological issues, but more importantly it increases the risk of skin cancer or photoaging. Severe burns significantly effect on the process of repigmentation as the pigmentation is tightly regulated by cell proliferation and differentiation of melanocytes and melanocyte stem cells which are housing in the epidermis and hair follicles of the skin. In the present review, we discuss the possible mechanisms to replenish the melanocytes from the healthy epidermis and hair follicles surrounding burn wounds. The molecular mechanisms of skin repigmentation following healing of burn injuries includes the differentiation of melanoblasts into melanocytes, the distribution and responses of melanocytes and melanocyte stem cells after burn injury, and the regulation of melanin production. We also reviewed advanced therapeutic strategies to treat pigmentation disorders, such as convectional surgery, laser, UV treatment and emerging concepts in skin tissue-engineering.

Differential expression of microRNA let-7b-5p regulates burn-induced hyperglycemia

One of the classical features observed in patients with burn injury is hyperglycemia. There have been previous reports that a cohort of microRNAs (miRNAs) is differentially expressed in the dermis of patients with burn injury. More specifically, it has been shown that the miR-194 can target the insulin-like growth factor receptor 1 (IGF1R) and silence its protein expression resulting in hyperglycemia. The objective of the current study was to discover if additional miRNA-mediated post-transcriptional mechanism exists that lead to suppression of IGF1R protein expression post-burn injury. Using the 30% total body surface area (TBSA) model of burn injury in rats we found that the miRNA let-7b can target IGF1R and downregulate its protein expression, in turn attenuating PI3K/Akt and Gsk3β activation leading to hyperglycemia. Increased let-7b expression was significantly more than the previously reported miR-194 both in the burn rats compared to sham and in patients with burn injury compared to healthy subjects. Serum from burn rats also resulted in decreased IGF1R protein expression in rat L6 myotubes. In vivo targeting of let-7b by antagomir mitigated the effect of increased let-7b expression on IGF1R protein expression and hyperglycemia. Thus targeting let-7b might be a promising approach to treat hyperglycemia in patients with burn injury.

[Effects of rapamycin and deferoxamin on wound healing after ischemia and hypoxia]

Objective

To explore the effect and mechanism of rapamycin and deferoxamin on wound healing after ischemia and hypoxia.

Methods

The model of ischemia and hypoxia wound was made on the back of 40 SPF male adult Sprague Dawley rats, weight (300±20) g; they were randomly divided into 4 groups ( n=10): the control group (group A), deferoxamine intervention group (group B), rapamycin intervention group (group C), and deferoxamine+rapamycin intervention group (group D). At 3, 6, and 9 days after model preparation, rats of groups A, B, C, and D were intra-peritoneally injected with normal saline, deferoxamin (10 mg/kg), rapamycin (3 mg/kg), deferoxamin (10 mg/kg)+rapamycin (3 mg/kg) respectively. The wound healing was observed and the healing time was recorded in each group; the wound healing tissue was harvested to test the mRNA and protein expressions of mammalian target of rapamycin (mTOR), hypoxia inducible factor 1α (HIF-1α), and vascular endothelial growth factor (VEGF) by real-time fluorescence quantitative PCR and Western blot at 2 days after wound healing.

Results

All rats survived to the end of the experiment, and wounds healed; the healing time of groups A, B, and D was significantly shorter than that of group C ( P<0.05), but there was no significant difference between groups A, B, and D ( P>0.05). Real-time fluorescence quantitative PCR showed that the expression of mTOR mRNA in groups C and D was significantly decreased when compared with the expressions in groups A and B ( P<0.05); there was significant difference between groups A and B ( P<0.05), but no significant difference between groups C and D ( P>0.05). The expressions of HIF-1α mRNA and VEGF mRNA were signi-ficantly higher in groups B and D than groups A and C, and in group A than group C ( P<0.05), but there was no signifi-cant difference between groups B and D ( P>0.05). Western blot showed that the relative expressions of mTOR protein in groups C and D were significantly decreased when compared with the expressions in groups A and B ( P<0.05), but there was no significant difference between groups C and D ( P>0.05). The relative expressions of HIF-1α protein in groups A, B, and C were significantly increased when compared with expression in group D ( P<0.05), but there was no significant difference between groups A, B, and C ( P>0.05). The relative expression of VEGF protein were significantly lower in groups B, C, and D than group A, in group D than groups B and C, and in group C than group B ( P<0.05).

Conclusion

Defe-roxamin can promote the wound healing of rats after ischemia and hypoxia, and the effect of rapamycin is opposite. It may be related to the existence of mTOR and HIF-1 signaling pathway in chronic ischemia-hypoxia wound.

Wound Healing Effects of Prunus yedoensis Matsumura Bark in Scalded Rats

Pruni Cortex has been used to treat asthma, measles, cough, urticaria, pruritus, and dermatitis in traditional Korean medicine. The objective of this study was to investigate the effects of Prunus yedoensis Matsumura bark methanol extract (PYE) on scald-induced dorsal skin wounds in rats. Scalds were produced in Sprague-Dawley rats with 100°C water and treated with 5% and 20% PYE (using Vaseline as a base), silver sulfadiazine (SSD), and Vaseline once a day for 21 days, beginning 24 hours after scald by treatment group allocation. The PYE-treated groups showed accelerated healing from 12 days after scald, demonstrated by rapid eschar exfoliation compared to the control and SSD groups. PYE-treated groups showed higher wound contraction rates and better tissue regeneration in comparison with the control group. Serum analysis showed that transforming growth factor beta 1 and vascular endothelial growth factor levels remained high or gradually increased up to day 14 in both PYE groups and then showed a sharp decline by day 21, implying successful completion of the inflammatory phase and initiation of tissue regeneration. These findings suggested that PYE is effective in promoting scald wound healing in the inflammation and tissue proliferation stages.

Nutrition and anabolic pharmacotherapies in the care of burn patients

Thermal injury is a devastating injury that results in a number of pathological alterations in almost every system in the body. Hypermetabolism, muscle wasting, depressed immunity, and impaired wound healing are all clinical features of burns. Failure to address each of these specific pathological alterations can lead to increased mortality. Nutrition supplementation has been recommended as a therapeutic tool to help attenuate the hypermetabolism and devastating catabolism evident following burn. Despite the wide consensus on the need of nutrition supplementation in burn patients, controversy exists with regard to the type and amount of nutrition recommended. Nutrition alone is also not enough in these patients to halt and reverse some of the damage done by the catabolic pathways activated following severe burn injury. This has led to the use of anabolic pharmacologic agents in conjunction with nutrition to help improve patient outcome following burn injury. In this review, we examine the relevant literature on nutrition after burn injury and its contribution to the attenuation of the postburn hypermetabolic response, impaired wound healing, and suppressed immunological responses. We also review the commonly used anabolic agents clinically in the care of burn patients. Finally, we provide nutrition and pharmacological recommendations gained from prospective trials, retrospective analyses, and expert opinions based on our practice at the Ross Tilley Burn Center in Toronto, Canada.

miR-194 Promotes burn-induced hyperglycemia via attenuating IGF-IR expression

Hyperglycemia is one of the most important clinical features of burn patients. Previous reports had demonstrated that miRNA was involved in regulating glucose metabolism in various diseases such as diabetes and obesity. Our current study discovered the relationship between miR-194 and hyperglycemia in burn rats via suppressing insulin-like growth factor 1 receptor (IGF-IR). We found that the fasting blood glucose was significantly increased in rats of the burn group, and protein expression of IGF-IR was attenuated in response to burn injury. Similar to the results of animal experiments, miR-194 expression was significantly elevated and IGF-IR protein level was suppressed in L6 cells treated with serum from burn rats compared with those treated by serum from sham rats. However, IGF-IR mRNA level was comparable between burn and sham rats, suggesting that IGF-IR may be downregulated at the translation level. Further experiments revealed that miR-194 was significantly increased in burn rats compared with sham rats using miRNA array and real-time polymerase chain reaction (PCR) assay. And IGF-IR protein expression was reduced in L6 cells transfected with miR-194 plasmid. Insulin-like growth factor 1 receptor expression was also repressed and fasting blood glucose was increased in rats injected with miR-194 plasmid. In general, we have identified a novel function of miR-194 in modulating burn-induced hyperglycemia via suppressing the expression of IGF-IR.

To cross-link or not to cross-link? Cross-linking associated foreign body response of collagen-based devices

Collagen-based devices, in various physical conformations, are extensively used for tissue engineering and regenerative medicine applications. Given that the natural cross-linking pathway of collagen does not occur in vitro, chemical, physical, and biological cross-linking methods have been assessed over the years to control mechanical stability, degradation rate, and immunogenicity of the device upon implantation. Although in vitro data demonstrate that mechanical properties and degradation rate can be accurately controlled as a function of the cross-linking method utilized, preclinical and clinical data indicate that cross-linking methods employed may have adverse effects on host response, especially when potent cross-linking methods are employed. Experimental data suggest that more suitable cross-linking methods should be developed to achieve a balance between stability and functional remodeling.

Gamma delta T cells regulate wound myeloid cell activity after burn

Major burns induce immune complications, which are associated with myeloid cell activation by ill-defined mechanisms. Although γδ T cells have been shown to be important in postinjury inflammation and wound healing, their role in the regulation of myeloid cells remains unknown. To study this, wild-type (WT) and γδ T cell-deficient (δTCR) mice were subjected to major burn (25% total body surface area, third degree) or sham treatment. At 3 days thereafter, skin samples were assayed for cytokine content or used to isolate single cells that were used for myeloid cell characterization by flow cytometry. The number of CD11b myeloid cells increased by approximately 75% in the wound skin of WT mice. This influx was caused by increased myeloid-derived suppressor cells (CD11b GR1) whose numbers increased 19-fold compared with those of sham skin. In contrast, macrophage (MØ; CD11b F4/80) numbers decreased by approximately 50% after burn. In δTCR mice, burn increased the myeloid cell numbers approximately 5-fold. The increase in myeloid cells at the injury site of δTCR mice was caused by both a myeloid-derived suppressor cell (50-fold) and a MØ (2-fold) influx. Burn increased skin cytokine levels for a number of prototypic inflammatory cytokines (interleukin 1β, interleukin 6, tumor necrosis factor-α, macrophage inflammatory protein [MIP] 1β, etc). Tumor necrosis factor-α, MIP-1α, and MIP-1β levels were further elevated (2- to 3-fold) in the injured skin of δTCR mice compared with those of WT mice. In conclusion, these data show that γδ T cells regulate myeloid cell infiltration of the wound site and act to quell inflammation, thereby promoting the transition to the proliferative phase of wound healing.

[Stimulation of adenosine receptors on myeloid cells enhance leukocyte migration at the site of burn injury]

Adenosine, endogenous purine nucleoside, is an ATP metabolite that also acts as an extracellular signaling molecule. The concentration of extracellular adenosine rises during hypoxia and cell damage leading to numerous pleiotropic effects. Although a high concentration of adenosine was found at burn injury, the effect has not been well elucidated. We have studied human peripheral blood myeloid cell, due to their expression of specific adenosine receptors and capacity to migrate to the site of burn injury. We have shown that myeloid cells after 72 hours of stimulation of adenosine receptors develop altered expression of surface antigens: preserved monocyte's marker CD14 with already expressed dendritic cell markers (CD209, CD1a). Whereas untreated cells have already lost monocyte marker in 72 hours, and express CD1a more abundantly. Adenosine modified myeloid cells express also higher levels of mRNA of proinflammatory cytokines and chemoattractants (IL-6, IL-8, IL-1 b). Using mouse model of the burn injury we have shown, that adenosine modified bone marrow derived myeloid cells injected in the site of the injury promote migration of granulocytes, monocytes, macrophages, and fibroblasts on the 7th day after burn. Thus, stimulation of adenosine receptors alters differentiation and function of myeloid cells. In the site of burn injury adenosine modified myeloid cells augment cell migration due to paracrine factors.

The burn wound inflammatory response is influenced by midazolam

Burn patients requiring hospitalization are often treated for anxiety with benzodiazepines (BDZs). Benzodiazepines are reported to influence immune system function. Immune system alterations are a major cause of burn-induced mortality. We wanted to determine whether the BDZ, midazolam given daily at an anxiolytic dose, had any influence on the burn injury-induced inflammatory response in the blood and wound. Mice received a 15% total body surface area flame burn and received either midazolam 1 mg/kg i.p. or saline 0.1 ml daily. Blood and skin wounds were harvested 24 h after injection on post-burn day 2, 3, 7, or 8. Mice treated with midazolam had significantly lower serum IL-1β (p=0.002), TNF-α (p=0.002), IL-6 (p=0.016), IL-10 (p=0.009), and TGF-β (p=0.004) than saline-treated mice, with little impact on serum chemokine levels. In the wound, TNF-α and IL-10 were the only cytokines significantly influenced by the drug, being lower (p=0.018) and higher (p=0.006), respectively. The chemokines in the wound influenced significantly by midazolam were MIP-1α, MIP-1β, and MIP-2 while MCP-1 and KC were not. There were more inflammatory cells at the burn wound margin in midazolam-treated mice on post-burn day 3. Although serum nitrate/nitrite was significantly increased by midazolam (p=0.03), both eNOS and iNOS mRNA expression in the wound were similar to the saline group. We found that midazolam given daily after burn injury significantly influenced the inflammatory response. The clinical implications of these findings on wound healing and shock following burn injury, especially larger burns, deserve further investigation.

Gamma delta (γδ) T-cells are critical in the up-regulation of inducible nitric oxide synthase at the burn wound site

BACKGROUND

The high incidence of morbidity and mortality following major burn can in part be attributed to immune derangements and wound healing complications. Inflammation plays an important role in wound healing, of which inducible nitric oxide synthase (iNOS) derived nitric oxide is a central mediator. T-cells of the γδ TCR lineage have also been shown to be important in healing of the burn wound site. Nonetheless, the role of γδ T-cells in the regulation of the burn wound iNOS expression is unknown.

METHODS

Wildtype (WT) and δ TCR(-/-) male C57BL/6 mice were subjected to burn (3rd degree, 12.5% TBSA) or sham treatment. Three days after injury, skin samples from non-injured and the burn wound were collected and analyzed for the expression of iNOS and cytokines and chemokine levels. In a second series of experiments, WT mice were subjected to burn and left untreated or treated with the iNOS inhibitor, L-Nil. Skin cytokine and chemokine levels were assessed 3days thereafter.

RESULTS

Burn induced an 18-fold increase in iNOS expression at the wound site as compared to the uninjured skin of WT sham mice. In δ TCR(-/-) mice iNOS expression at the wound site was significantly lower than that of the WT group. Burn also induced increased levels of IL-1β, IL-6, G-CSF, TNF-α, KC, MCP-1, MIP-1α and MIP-1β at the wound site in WT and δ TCR(-/-) mice, but G-CSF, TNF-α, and MIP-1β levels were greater in δ TCR(-/-) mice. Inhibition of iNOS activity in WT mice with L-Nil suppressed burn wound levels of IL-1β, G-CSF, and MIP-1α, whereas IL-6, TNF-α, KC, MCP-1 and MIP-1β were unaffected.

CONCLUSIONS

T-cells of the γδ TCR lineage significantly contribute to the up-regulation of iNOS expression which contributes to wound inflammation.

Interferon-gamma inhibits healing post scald burn injury

Impaired healing after severe burns remains a reason for prolonged hospitalization, opportunistic infections, and debilitating scarring. Interferon-gamma (IFN-γ) is an important immune regulator that has been shown to inhibit collagen synthesis by fibroblasts, resulting in delayed healing in incision wounds. To determine whether IFN-γ plays similar roles in the healing process after severe burn, we induced scald injury in mice deficient or sufficient in IFN-γ and examined local responses. In the absence of IFN-γ, scalded areas healed faster. This was associated with attenuated local inflammatory responses, enhanced reepithelialization, increased proliferation of keratinocytes in reepithelialized leading edges, and up-regulation of growth factors in burned skin areas. Furthermore, angiogenesis and myofibroblast formation commenced and terminated earlier in IFN-γ(-/-) mice compared with wild type (WT) controls. Our observations demonstrate that inhibition of IFN-γ results in accelerated healing after burn injury by dampening excessive inflammation and facilitating reepithelialization, collagen deposition, and wound contraction.

Hypoxia inducible factor-1α contributes to UV radiation-induced inflammation, epidermal hyperplasia and immunosuppression in mice

Hypoxia inducible factor-1α (HIF-1α), a ubiquitous inducible oxygen-sensing transcription factor, promotes cell survival under hypoxic conditions, including the early pre-angiogenic period of tumorigenesis, and is known to contribute to many malignancies. However HIF-1α can also be activated by inflammatory mediators, and can activate inflammation-modulating proteins itself, including heme oxygenase-1 (HO-1) and the cytokine IL-6. Recently HIF-1α was reported to be induced by UVB (290-320 nm) radiation in cultured human keratinocytes, acting as a stress protein associated with the release of reactive oxygen species. In this in vivo murine study we demonstrate that HIF-1α protein is an early responder to UV radiation in the skin, and its activation can be attenuated by treating mice with its post-translational inhibitor, YC-1. Treatment with YC-1 following UV-irradiation of mice has revealed the involvement of HIF-1α in UV-induced inflammation, IL-6 production, and epidermal hyperplasia. In addition, upregulated cutaneous HIF-1α was found to be an important factor in the UV-suppression of T cell-mediated immunity, measured by contact hypersensitivity (CHS). The mechanism remains unclear, however it did not appear to involve the immunosuppressive cutaneous photoproduct cis-urocanic acid, but HIF-1α induction was inhibited by irradiation with photoimmune protective UVA (320-400 nm), implicating a negative correlation between the two stress proteins, HIF-1α and the photoimmune protective UVA responder HO-1.

Tie2-dependent knockout of HIF-1 impairs burn wound vascularization and homing of bone marrow-derived angiogenic cells

AIMS

Hypoxia-inducible factor 1 (HIF-1) is a heterodimer composed of HIF-1α and HIF-1β subunits. HIF-1 is known to promote tissue vascularization by activating the transcription of genes encoding angiogenic factors, which bind to receptors on endothelial cells (ECs) and bone marrow-derived angiogenic cells (BMDACs). In this study, we analysed whether HIF-1 activity in the responding ECs and BMDACs is also required for cutaneous vascularization during burn wound healing.

METHODS AND RESULTS

We generated mice with floxed alleles at the Hif1a or Arnt locus encoding HIF-1α and HIF-1β, respectively. Expression of Cre recombinase was driven by the Tie2 gene promoter, which is expressed in ECs and bone marrow cells. Tie2Cre(+) and Tie2Cre(-) mice were subjected to burn wounds of reproducible diameter and depth. Deficiency of HIF-1α or HIF-1β in Tie2-lineage cells resulted in delayed wound closure, reduced vascularization, decreased cutaneous blood flow, impaired BMDAC mobilization, and decreased BMDAC homing to burn wounds.

CONCLUSION

HIF-1 activity in Tie2-lineage cells is required for the mobilization and homing of BMDACs to cutaneous burn wounds and for the vascularization of burn wound tissue.

Burn-induced alterations in toll-like receptor-mediated responses by bronchoalveolar lavage cells

Burn is associated with profound inflammation and activation of the innate immune system in multiple organ beds, including the lung. Similarly, toll-like receptors (TLR) are associated with innate immune activation. Nonetheless, it is unclear what impact burn has on TLR-induced inflammatory responses in the lung.

METHODS

Male C57BL/6 mice were subjected to burn (3rd degree, 25% TBSA) or sham procedure and 1, 3 or 7 days thereafter, bronchoalveolar lavage (BAL) fluid was collected and cells were isolated and cultured in vitro with specific TLR agonists as follows: Zymosan (TLR-2), LPS (TLR-4) and CpG-ODN (TLR-9). Supernatants were collected 48 h later and assayed for inflammatory cytokine levels (IL-1β, IL-6, IL-10, IL-17, TNF-α, KC, MCP-1, MIP-1α, MIP-1β and RANTES) by Bioplex.

RESULTS

BAL fluid from sham and burn mice did not contain detectable cytokine levels. BAL cells, irrespective of injury, were responsive to TLR-2 and TLR-4 activation. Seven days after burn, TLR-2 and TLR-4 mediated responses by BAL cells were enhanced as evidenced by increased production of IL-6, IL-17, TNF-α, MCP-1, MIP-1β and RANTES.

CONCLUSIONS

Burn-induced changes in TLR-2 and TLR-4 reactivity may contribute to the development of post-burn complications, such as acute lung injury (ALI) and adult respiratory distress syndrome (ARDS).

Aging impairs the mobilization and homing of bone marrow-derived angiogenic cells to burn wounds

Impaired wound healing in the elderly represents a major clinical problem. Delineating the cellular and molecular mechanisms by which aging impairs wound healing may lead to the development of improved treatment strategies for elderly patients with non-healing wounds. Neovascularization is an essential step in wound healing, and bone marrow-derived angiogenic cells (BMDACs) play an important role in vascularization. Using a mouse full-thickness burn wound model, we demonstrate that perfusion and vascularization of burn wounds were impaired by aging and were associated with dramatically reduced mobilization of BMDACs bearing the cell surface molecules CXCR4 and Sca1. Expression of stromal-derived factor 1 (SDF-1), the cytokine ligand for CXCR4, was significantly decreased in peripheral blood and burn wounds of old mice. Expression of hypoxia-inducible factor (HIF)-1α was detected in burn wounds from young (2-month-old), but not old (2-year-old), mice. When BMDACs from young donor mice were injected intravenously, homing to burn wound tissue was impaired in old recipient mice, whereas the age of the BMDAC donor mice had no effect on homing. Our results indicate that aging impairs burn wound vascularization by impairing the mobilization of BMDACs and their homing to burn wound tissue as a result of impaired HIF-1 induction and SDF-1 signaling.

Wound trauma mediated inflammatory signaling attenuates a tissue regenerative response in MRL/MpJ mice

Background

Severe trauma can induce pathophysiological responses that have marked inflammatory components. The development of systemic inflammation following severe thermal injury has been implicated in immune dysfunction, delayed wound healing, multi-system organ failure and increased mortality.

Methods

In this study, we examined the impact of thermal injury-induced systemic inflammation on the healing response of a secondary wound in the MRL/MpJ mouse model, which was anatomically remote from the primary site of trauma, a wound that typically undergoes scarless healing in this specific strain. Ear-hole wounds in MRL/MpJ mice have previously displayed accelerated healing and tissue regeneration in the absence of a secondary insult.

Results

Severe thermal injury in addition to distal ear-hole wounds induced marked local and systemic inflammatory responses in the lungs and significantly augmented the expression of inflammatory mediators in the ear tissue. By day 14, 61% of the ear-hole wounds from thermally injured mice demonstrated extensive inflammation with marked inflammatory cell infiltration, extensive ulceration, and various level of necrosis to the point where a large percentage (38%) had to be euthanized early during the study due to extensive necrosis, inflammation and ear deformation. By day 35, ear-hole wounds in mice not subjected to thermal injury were completely closed, while the ear-hole wounds in thermally injured mice exhibited less inflammation and necrosis and only closed partially (62%). Thermal injury resulted in marked increases in serum levels of IL-6, TNFα, KC (CXCL1), and MIP-2α (CXCL2). Interestingly, attenuated early ear wound healing in the thermally injured mouse resulted in incomplete tissue regeneration in addition to a marked inflammatory response, as evidenced by the histological appearance of the wound and increased transcription of potent inflammatory mediators.

Conclusion

These findings suggest that the observed systemic inflammatory response of a severe thermal injury undoubtedly has an adverse effect on wound healing and tissue regeneration.

Impaired angiogenesis and mobilization of circulating angiogenic cells in HIF-1alpha heterozygous-null mice after burn wounding

Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that controls vascular responses to hypoxia and ischemia. In this study, mice that were heterozygous (HET) for a null allele at the locus encoding the HIF-1alpha subunit (HET mice) and their wild-type (WT) littermates were subjected to a thermal injury involving 10% of the body surface area. HIF-1alpha protein levels were increased in burn wounds of WT but not of HET mice on day 2. The serum levels of stromal-derived factor 1alpha, which binds to CXCR4, were increased on day 2 in WT but not in HET mice. Circulating angiogenic cells were also increased on day 2 in WT but not in HET mice and included CXCR4(+)Sca1(+) cells. Laser Doppler perfusion imaging demonstrated increased blood flow in burn wounds of WT but not HET mice on day 7. Immunohistochemistry on day 7 revealed a reduced number of CD31(+) vessels at the healing margin of burn wounds in HET as compared with WT mice. Vessel maturation was also impaired in wounds of HET mice as determined by the number of alpha-smooth muscle actin-positive vessels on day 21. The remaining wound area on day 14 was significantly increased in HET mice compared with WT littermates. The percentage of healed wounds on day 14 was significantly decreased in HET mice. These data delineate a signaling pathway by which HIF-1 promotes angiogenesis during burn wound healing.