Burn-Induced Gut Mucosal Homeostasis in TCR ?? Receptor-Deficient Mice

A comparative study of pentoxifylline effects in adult and aged rats submitted to lung dysfunction by thermal injury

PURPOSE

To investigate the protective effects of pentoxifylline against lung injury observed after dorsal scald in aged animals.

METHODS

Adult (eight months old) and aged (20 months old) rats were subjected to thermal injury or sham procedure. The six hours post-trauma animals received pentoxifylline and after 24 hours were euthanatized and lung tissue samples collected. The bronchoalveolar lavage fluid was evaluated for total protein content and tumor necrosis factor-alpha cytokine. Malondialdehyde and myeloperoxidase activity in the lung homogenate were measured and a histological lung examination was undertaken.

RESULTS

Burn injury induced oxidative stress in lung homogenate was higher in elderly-burned rats compared to adult-burned rats (p<0.001). Total protein and cytokine in bronchoalveolar lavage increased in the elderly-burned group when compared to the adult-burned group (p<0.001). All parameters decreased in both groups treated with pentoxifylline (p<0.05).

CONCLUSIONS

The injury was augmented in elderly rats when compared to adult rats. Damage was reduced with the use of pentoxifylline, however further studies are needed to evaluate the dose-response of the drug.

Vagal nerve stimulation blocks peritoneal macrophage inflammatory responsiveness after severe burn injury

Large surface area burn injuries lead to activation of the innate immune system, which can be blocked by parasympathetic inputs mediated by the vagus nerve. We hypothesized that vagal nerve stimulation (VNS) would alter the inflammatory response of peritoneal macrophages after severe burn injury. Male BALB/c mice underwent right cervical VNS before 30% total body surface area steam burn and were compared with animals subjected to burn alone. Peritoneal macrophages were harvested at several time points following injury and exposed to lipopolysaccharide (LPS) in culture conditions. The inflammatory response of peritoneal macrophages was measured by analyzing changes in nuclear factor κB p65 phosphorylation using flow cytometry. We found that peritoneal macrophages isolated from mice subjected to burn injury were hyperresponsive to LPS challenge, suggesting burn-induced macrophage activation. We identified a protective role for VNS in blocking peritoneal macrophage activation. Analysis of the phosphorylation state of nuclear factor κB pathway mediator, p65 Rel A, revealed a VNS-mediated reduction in p65 phosphorylation levels after exposure to LPS compared with burn alone. In combination, these studies suggest VNS mediates the inflammatory response in peritoneal macrophages by affecting the set point of LPS responsiveness.

Skeletal muscle satellite cell activation following cutaneous burn in rats

BACKGROUND

Cutaneous burn distant from skeletal muscles induces atrophy; however, its effect on muscle stem cells resident in skeletal muscle (satellite cells) distal to burn is not known.

METHODS

Satellite cell activation was measured in predominantly fast-twitch [tibialis anterior, extensor digitorum longus (EDL), plantaris, and gastrocnemius] and slow-twitch (soleus) muscles of rats that received either 40% total body surface area full-thickness scald burn or sham burn to the trunk area by determining bromodeoxyuridine incorporation, MyoD, and Pax7 immunohistochemistry in vivo ≤48 h after burn. To determine the effects of circulating factors on satellite cell activation, satellite cell cultures were treated with serum from sham or burn rats.

RESULTS

In vivo activation of satellite cells was increased in fast muscles isolated from burn as compared to sham animals, whereas a significant response was not seen in slow muscles. Serum taken from animals in the burn group increased the activation of satellite cells isolated from both sham and burn animals in vitro, suggesting that circulating factors have the potential to increase satellite cell activation following burn.

CONCLUSIONS

Increases in satellite cell activation in muscles distal to burn are fiber-type-dependent, and circulating factors may play a role in the activation of satellite cells following burn. A better understanding of the impact of burn on satellite cell functionality will allow us to identify the cellular mechanisms of long-term muscle atrophy.

The biology of burn injury

Burn injury is a complex traumatic event with various local and systemic effects, affecting several organ systems beyond the skin. The pathophysiology of the burn patient shows the full spectrum of the complexity of inflammatory response reactions. In the acute phase, inflammation mechanism may have negative effects because of capillary leak, the propagation of inhalation injury and the development of multiple organ failure. Attempts to mediate these processes remain a central subject of burn care research. Conversely, inflammation is a necessary prologue and component in the later-stage processes of wound healing. In this review, we are attempting to present the current science of burn wound pathophysiology and wound healing. We also describe the evolution of innovative strategies for burn management.

Proximal gut mucosal epithelial homeostasis in aged IL-1 type I receptor knockout mice after starvation

BACKGROUND

Previous studies have shown that starvation induces small bowel atrophy, and that atrophy diminishes with aging. In this experiment, we assessed whether starvation-induced atrophy of proximal gut mucosa is associated with the Interleukin-1 receptor (IL-1R) signaling pathway in aged mice.

MATERIALS AND METHODS

Thirty 26-month-old IL-1R knockout mice and age-matched wild-type C57BL/6 mice were randomly divided into two groups: ad libitum fed and fasted. Mice were euthanized 12 or 48 hours after starvation. The proximal small bowel was harvested for morphologic analysis. Gut epithelial cell proliferation was detected using immunohistochemical staining for proliferating cell nuclear antigen (PCNA), and apoptosis was identified using terminal deoxyuridine nick-end labeling (TUNEL) staining.

RESULTS

Aged IL-1R knockout mice were larger than aged-matched wild-type mice (P < 0.05). Proximal gut mucosal height and mucosal cell number were not different between aged IL-1R knockout and wild-type groups. The apoptosis index in gut epithelial cells was higher in fed IL-1R knockout versus wild-type mice (P < 0.05), while there was no significant difference in cell proliferation between both groups. Mucosal atrophy was induced in both aged IL-1R knockout and wild-type groups by starvation (P < 0.05), however, aged IL-1R knockout mice experienced greater loss in proximal gut weight, mucosal length, and corresponding cell number than did wild-type mice at the 12-h time point (P < 0.05). The apoptosis index in gut epithelial cells significantly increased in both groups after starvation (P < 0.05). Starvation decreased cell proliferation in IL-1R knockout mice (P < 0.05), but not in wild-type mice.

CONCLUSIONS

The response in aged IL-1R knockout mice differs from wild-type mice in that starvation increases atrophy and is associated with decreased cell proliferation rather than increased apoptosis.

Burn-induced gut barrier injury is attenuated by phosphodiesterase inhibition: effects on tight junction structural proteins

Loss of intestinal barrier function after burn injury allows movement of intraluminal contents across the mucosa, which can lead to the development of distant organ injury and multiple organ failure. Tight junction function is highly regulated by membrane-associated proteins including occludin and zonula occludens protein 1 (ZO-1), which can be modulated by systemic inflammation. We hypothesized that (1) burn injury leads to gut barrier injury, and (2) phosphodiesterase inhibition will attenuate these burn-induced changes. Male balb/c mice undergoing a 30% steam burn were randomized to resuscitation with normal saline or normal saline + pentoxifylline (PTX; 12.5 mg/kg). Intestinal injury was assessed by histological diagnosis and TNF-alpha levels using enzyme-linked immunosorbent assay. Intestinal permeability was assessed by measuring the plasma concentration of fluorescein isothiocyanate-dextran after intraluminal injection in the distal ileum. Occludin and ZO-1 levels were analyzed by immunoblotting and immunohistochemistry. Thirty percent total body surface area (TBSA) burn results in a significant increase in intestinal permeability. Treatment with PTX after burn attenuates intestinal permeability to sham levels. Burn injury resulted in a marked decrease in the levels of tight junction proteins occludin and ZO-1 at 6 and 24 h. The use of PTX after burn significantly decreases the breakdown of occludin and ZO-1. Pentoxifylline also attenuates the burn-induced increase in plasma and intestinal TNF-alpha. Confocal microscopy demonstrates that PTX attenuates the burn-induced reorganization of occludin and ZO-1 away from the tight junction. Pentoxifylline attenuates burn-induced intestinal permeability and decreases the breakdown and reorganization of intestinal occludin and ZO-1. Therefore, phosphodiesterase inhibition may be a useful adjunct strategy in the attenuation of burn-induced gut barrier injury.

Gammadelta T-cells: potential regulators of the post-burn inflammatory response

Severe burn induces an immunopathological response that contributes to the development of a systemic inflammatory response (SIRS) and subsequent multiple organ failure. While, multiple immune cells type (T-cells, macrophages, neutrophils) are involved in this response, recent evidence suggests that a unique T-cell subset, gammadelta T-cells are central in the response to injury. While gammadelta T-cells represent only a small percentage of the total T-cell population, they display specific functional characteristics that uniquely position them in the immune/inflammatory axis to influence a number of important aspects of the body's response to burn. This review will focus on the potential regulator role of gammadelta T-cells in immunopathological response following burn and thereby their potential as therapeutic targets for affecting inflammation and healing.

Regulatory T cell populations in sepsis and trauma

Sepsis syndrome remains the leading cause of mortality in intensive care units. It is now believed that along with the body's hyperinflammatory response designated to eliminate the underlying pathogen, mechanisms are initiated to control this initial response, which can become deleterious and result in immune dysfunctions and death. A similar state of immune suppression has been described after numerous forms of severe trauma/injury. Although the evidence for immune dysfunctions after sepsis has grown, much remains to be understood about mechanisms underpinning its development and how it acts to increase the morbid state of the critically ill patient. In this context, although the majority of clinical and basic science conducted so far has focused on the roles of myeloid cell populations, the contribution of T lymphocytes and in particular, of regulatory T cells has been somewhat ignored. The studies presented here support the concept that regulatory T lymphocytes (CD4+CD25+ regulatory, gammadelta, and NK T cells) play a role in the control of immune responses and are affected by injury and sepsis. This may be related to their capacity to interact with components of the innate and adaptive immune responses and to their ability to be activated nonspecifically by bacterial products and/or cytokines and to regulate through direct cell-cell and/or soluble mediators. It is our hope that a better understanding of the mechanism through which those rare lymphocyte subsets exert such a profound effect on the immune response may help in improving our ability not only to diagnose but also to treat the critically ill individual.

Innate Lymphocyte Subsets and Their Immunoregulatory Roles in Burn Injury and Sepsis

The vast majority of clinical and basic science research on the immune consequences of burn injury and sepsis conducted during the last three decades has focused mainly on the roles of macrophages, neutrophils and, to a lesser extent, conventional T lymphocytes. During recent years, however, it has become increasingly clear that minor subsets of innate immune cells, innate regulatory lymphocytes in particular, are central to processes involved in both protective immunity and immunopathology. Recent reports by our laboratory and others have just begun to shed light on the critical roles of innate lymphocyte subsets, including natural killer T cells, natural killer cells, gamma-delta T cells, and naturally occurring CD4+CD25+ regulatory T cells during the immune response to burn injury and sepsis. Given their emerging importance and documented upstream regulatory capacities over macrophage, dendritic cell, and T lymphocyte functions, innate regulatory lymphocytes represent attractive new targets for therapeutic intervention for the overall immune paralysis that occurs with injury and sepsis. Here, we provide an overview of the current state of knowledge of these particular cell subsets in the immune response to burn injury and sepsis.

“Systemic apoptotic response” after thermal burns

The systemic pathophysiologic changes following thermal injuries affect multiple organs and body systems leading to clinical manifestations including shock, intestinal alterations, respiratory and renal failure, immunosuppression and others. Recent advances in the comprehension of mechanisms underlying systemic complications of thermal injuries have contributed to uncover part of the cellular and molecular basis that underlie such changes. Recently, programmed cell death (apoptosis) has been considered playing an important role in the development of such pathological events. Therefore, investigators utilizing animal models and clinical studies involving human primates have produced a large body of information suggesting that apoptosis is associated with most of the tissue damages triggered by severe thermal injuries. In order to draw the attention on the important role of apoptosis on systemic complications of thermal injuries, in this review we describe most of these studies, discuss possible cellular and molecular mechanisms and indicate ways to utilize them for the development of therapeutic strategies by which apoptosis may be prevented or counteracted.

Epithelial and mucosal gamma delta T cells

Although they constitute a small part of the circulating lymphocyte population, gammadelta T cells are found in high abundance on mucosal and epithelial surfaces. These gammadelta T cells are activated in response to stress to the surrounding tissue and perform a number of functions depending upon the location and type of stress that has occurred. Roles elucidated recently for gammadelta T cells include modulation of epithelial homeostasis through insulin-like growth factor-1 and keratinocyte growth factor, lysis of cytomegalovirus-infected cells, and recruitment of inflammatory cells to sites of tissue damage. Recent advances have provided an understanding of the development of mucosal and skin gammadelta T cells and their roles in restoring and maintaining tissue integrity.

Transgenic and gene knock-out techniques and burn research

The development of transgenic technology has given researchers a powerful tool to examine biological effects, and the response to injury is no exception. Techniques such as pronuclear injection, targeted homologous recombination, and Cre/loxP gene excision are being used to construct animals with specific genetic designs; these are exploited to learn the role of genes in the response to severe burn. We review the construction of transgenic animals, pitfalls and benefits of this relatively new technique, and how this technique has been used in burn research.