Impact of burn injury on hepatic TGF-beta1 expression and plasma TGF-beta1 levels

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.

The function of miRNAs and their potential as therapeutic targets in burn-induced insulin resistance (review)

Burns are common accidental injuries. The main clinical manifestations of severe burn injury are insulin resistance and high metabolism. Insulin resistance results in hyperglycemia, which may lead to skeletal muscle wasting and suspended wound healing. It also elevates the risk of infection and sepsis. Studies have indicated that insulin receptor (IR) and insulin receptor substrate 1 (IRS1) are essential factors involved in the regulation of blood glucose levels. Moreover, the suppression of the IR/IRS1 signaling pathway results in insulin resistance. Recent studies have also indicated that miRNAs, which are small non-coding RNAs consisting of 20-23 nucleotides, target the 3'-untranslated region (3'-UTR) of IRS1 mRNA and attenuate protein translation. miRNAs also play an important role in the development of type II diabetes (T2D) and obesity-induced insulin resistance. In the present review, we discuss the involvement of miRNAs in burn-induced insulin resistance through the targeting of the IR/IRS1 signaling pathway. We also discuss the possibility of miRNAs a novel therapeutic target in insulin resistance in burn patients.

Burn injury differentially alters whole-blood and organ glutathione synthesis rates: An experimental model

Previous studies from our laboratories revealed a reduced rate of whole-blood (WB) glutathione (GSH) synthesis in severely burned patients. To determine whether WB GSH metabolism is an indicator of the status of GSH metabolism in one or more of the major organs, we used a burn rabbit model to determine GSH concentrations and rates of synthesis in WB, liver, lungs, kidney, and skeletal muscle. L-[1-¹³C]-cysteine was infused intravenously for 6 h in rabbits at 3 days post-burn and in sham burn controls. WB and organ ¹³C-enrichment of cysteine and GSH was determined by gas chromatography/mass spectrometry. Plasma cysteine metabolic flux was increased significantly (P < 0.01) following burn injury. WB, liver, and lung GSH concentrations (P = 0.054, P < 0.05, and P < 0.05, respectively) and fractional rates of GSH synthesis (P < 0.05, P < 0.01, and P < 0.05, respectively) were reduced at 3 days post-burn. Kidney was unaffected. There also appears to be an increased rate of GSH transport out of the liver after burn injury. Hence, there is a differential impact of burn injury on tissue and organ GSH status, with WB qualitatively reflecting the changes in lung and liver. It will be important to determine whether these changes are due to alterations in the intrinsic capacity for GSH synthesis and/or availability of amino acid precursors of GSH.

Longitudinal changes in plasma Transforming growth factor beta-1 and post-burn scarring in children

Transforming growth factor beta1, a multifunctional growth factor, plays a pivotal role in wound healing and has been shown to accelerate impaired wound healing. However, high systemic levels of Transforming growth factor beta1 have generally been associated with fibrotic disease processes such as myelofibrosis and pulmonary fibrosis. Hypertrophic scarring occurring during childhood interferes with growth, impairs the function and causes immense psychological and aesthetic problems. Burns is the leading cause of hypertrophic scarring. We studied the longitudinal relationship between plasma Transforming growth factor beta-1 and post-burn wound healing and scarring in children. We discovered that the plasma levels of Transforming growth factor beta-1 rapidly increased to significantly higher levels in the first two weeks post-injury and fell thereafter, in patients who healed with good quality scars post-burn. By contrast, the increase in plasma TGFbeta1 levels in the early stages after-burn, was noticeably absent in patients who developed hypertrophic scarring. We propose that this change in the systemic levels of TGFbeta1 early after the burn may be used as an indicator of patients at risk of developing hypertrophic burn scars. This group of patients could then be targeted for early pharmacological/physical interventions to reduce/prevent scar-related morbidity in burn survivors.

“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.

The effects of transforming growth factor-beta neutralization on postburn humoral immunity

BACKGROUND

Burn injury induces immunosuppression, which is associated with an increased susceptibility to infection. Our laboratory has demonstrated that burn injury also impairs humoral immunity. We reported that burn injury enhanced expression of transforming growth factor-beta (TGF-beta) mRNA and that exogenous TGF-beta further impaired humoral immunity. The objective of this study was to clarify the role of TGF-beta on humoral immunity after burn injury with a neutralizing experiment.

METHODS

Twelve BALB/c mice were randomly divided into two groups: sham and burn. Anesthetized mice received a 20% full-thickness burn or sham injury. The murine splenocytes containing 1.5 x 10 cells/mL were cultured with 2.5 microg/mL of lipopolysaccharide with or without 0.5 ng/mL of TGF-beta or 1 microg/mL of anti-TGF-beta neutralizing antibody, if necessary. Concentrations of immunoglobulin (Ig) M in the cell culture supernatant were determined by enzyme-linked immunosorbent assay and the number of IgM-secreting cells in the culture was measured by enzyme-linked immunospot assay.

RESULTS

After 2-day culture, neutralization of TGF-beta dramatically restored IgM synthesis after burn injury. After 5-day culture, however, it restored IgM concentration but failed to restore a number of IgM-secreting cells.

CONCLUSION

This neutralizing experiment demonstrated that TGF-beta is one of the inhibitors of IgM synthesis after burn injury. However, neutralization of TGF-beta was not enough to completely restore humoral immunity after burn injury. Investigation of the mechanism of impaired IgM synthesis after burn injury should be continued.

Reduced Hepatic Expression of Glutathione S-Transferases in Burned Mice

BACKGROUND

Glutathione S-transferases (GSTs) contribute to liver homeostasis and are released into plasma after liver injury. This study investigates the hepatic expression of key GST enzyme subtypes after burn injury.

METHODS

Mice were subjected to an 18% total body surface area burn. Expression of mGSTalpha3 and mGSTmu1 was analyzed by reverse-transcriptase polymerase chain reaction and Western blots on liver preparations from burned and control mice. GST catalytic activity was measured by conjugation assays.

RESULTS

: In burned animals, mGSTalpha3 mRNA was only reduced at 1 day, whereas mGSTmu1 mRNA decreased at 1 day and at 3 days after injury. Total mGSTmu protein levels decreased at the same time points, whereas total mGSTalpha protein levels did not change. Also, by 3 days, total GST conjugation activity was reduced by 25% (p=0.05).

CONCLUSION

Reduced expression of specific alpha and mu GST enzymes after burns correlates functionally with reduced GST activity. Altered GST expression may contribute to liver damage after systemic injury.

Altered serum transforming growth factor-beta1 and monocyte chemoattractant protein-1 levels in obstructive jaundice

Impaired immune function has long been documented in patients with obstructive jaundice, and those with jaundice due to extrahepatic biliary obstruction still experience a high rate of postoperative complications and death. Transforming growth factor-beta1 (TGFbeta1) appears to be an important regulator of both normal and pathologic conditions in the liver. Monocyte chemoattractant protein-1 (MCP-1) is an important mediator of monocyte recruitment to inflammatory sites. We hypothesize that obstructive jaundice may alter serum TGFbeta1 and MCP-1 expressions in the rat and that oral bile acid or glutamine (or both) can restore the altered serum TGFbeta1 and MCP-1 expression in rats with obstructive jaundice. Male Sprague-Dawley rats weighing 250 to 300 g were randomized to four groups (n = 10 in each group). Group 1 underwent a sham operation with oral normal saline administration. Group 2 underwent common bile duct ligation (CBDL) with oral normal saline administration. Group 3 underwent CBDL with oral bile acid replacement. Group 4 underwent CBDL with oral glutamine administration. Animals were sacrificed after 3 days (n = 5) and 7 days (n = 5), and blood samples were collected. Serum was obtained after centrifugation for measurement of TGFbeta1 and MCP-1 levels by an enzyme-linked immunosorbent assay. The serum TGFbeta1 level was significantly elevated (p = 0.006) 3 days after CBDL. Oral glutamine administration prevented this elevation, but oral bile acid replacement did not. The serum MCP-1 level showed similar changes. After 3 days of obstructive jaundice, the TGFbeta1 and MCP-1 levels were altered in the rat. Oral glutamine administration, not oral bile acid replacement, was able to prevent these alterations.

Transforming growth factor-beta1 and major trauma: time-dependent association with hepatic and renal insufficiency

Dysbalance in the immune system is perceived as a major factor for adverse outcome after trauma. Transforming growth factor-beta1 (TGF-beta1) is a multifunctional cytokine that regulates proliferation, differentiation of cells, wound healing, and angiogenesis. The influence of TGF-beta1 on trauma patients outcome is still unclear. Injury patterns and clinical outcome parameters of 99 consecutive patients with life-threatening injury and an injury severity score (ISS) > 15 were assessed in a prospective, single-center study at a Level I trauma center. Levels of TGF-beta1 in plasma were measured over a 5-day period by an enzyme-linked immunoabsorbant assay (ELISA). TGF-beta1 plasma levels rise shortly after trauma and gradually drop as the 5th day approaches. Mean and maximal TGF-beta1 plasma levels were significantly higher in patients who developed sepsis and were significantly lower in patients with renal or hepatic failure. Receiver operating characteristics-curve analysis of liver failure shows an area under the curve (AUC) of 0.68 (95%: 0.55-0.81, P = 0.02) and of an AUC of 0.63 (95%: 0.52-0.75, P = 0.03) for renal failure for maximal TGF-beta1 plasma (initial until day 2) levels if lower values represent a more positive test. The data indicate that the increase and decrease of TGF-beta1 plasma levels may contribute to clinical outcome after severe injury. Lower TGF-beta1 levels are associated with liver and renal insufficiency. Higher TGF-beta1 levels 6 h after ICU admission increase the risk of sepsis. TGF-beta1 seems to be an early onset reactant and not a second-line responsive cytokine.

Effects of full-thickness burns on nociceptor sensitization in anesthetized rats

Burn-induced pain is often inadequately managed and its mechanisms, both peripheral and central, are poorly understood. To examine peripheral mechanisms, the effects of full-thickness burns on individual nociceptive fibers in sural nerve of anesthetized rats were studied. Additionally, the study investigated whether topical post-burn treatment with the mu-opioid receptor agonist loperamide ameliorated burn-induced pathologies. Receptive field (RF) properties of C-fibers were determined for 4h before and after producing burns. Burns caused profound tissue damage with edema extending beyond the injury site. Injury located within or proximal to RFs of nociceptors caused rapid decreases in mechanical responsiveness or complete desensitization at the original test site. However, post-burn, RF size frequently grew to include areas of newly sensitized skin. Transient or prolonged periods of ectopic activity was recorded from some nociceptors; this was most prevalent in fibers with RFs proximal to the injury site where burn induced background firing in 60% of the population. In most cases, loperamide significantly increased mechanical thresholds, prevented sensitization of uninjured skin, and reduced discharge.These data indicate that full-thickness burns activate and/or sensitize C-nociceptors, thus probably leading to pain. As loperamide ameliorates nociceptor activation and sensitization, it is an appropriate candidate for burn pain management.

Deficient transforming growth factor beta and interleukin-10 responses contribute to the septic death of burned patients

In order to understand the roles of pro-inflammatory and anti-inflammatory cytokines in burn injury and sepsis post-burn, serial changes in serum levels of transforming growth factor beta-1 (TGF-beta-1) were determined and compared to those of IL-6 and IL-10 in 15 burned patients. Among these 15 patients, 8 recovered without sepsis. The other seven, who were septic, expired. Our results showed that an initial peak serum TGF-beta-1 response was detected within 1 day post-burn. Peak serum IL-6 and IL-10 responses were also detected within 4 days after the burn injury of these patients. Significant differences in peak serum IL-6, IL-10 and TGF-beta-1 levels were not found between patients with total body surface area (TBSA) of greater or less than 50% and between patients who survived or expired from burn injury. Afterwards, levels of circulating IL-6 and IL-10 remained low in the survivors. However, a second peak response in serum TGF-beta-1 levels was observed in all burned patients analyzed. The second peak serum TGF-beta-1 levels post-burn of the eight survivors and the seven non-survivors were from 28,542 to 76,554 pg/ml (a mean value of 51,256+/-14,264 pg/ml) and from 8616 to 40,851 pg/ml (a mean value of 24,079+/-10,399 pg/ml), respectively. A significant difference (P<0.01) in mean values of the second peak TGF-beta-1 responses between groups of survivors and non-survivors was detected. Levels of circulating IL-6 in the septic non-surviving patients showed a tendency to increase 1-2 weeks post-burn and reached high levels before the expiration of these patients. After an initial peak response, the serum IL-10 level remained low in one of the seven non-survivors, while it increased in the other six non-survivors. However, marked increases in circulating IL-10 levels were observed only just before the death of these non-survivors. In conclusion, an initial increase in serum levels of IL-6, IL-10 and TGF-beta-1 was detected post-burn. A marked increase in serum levels of IL-6 before death suggests its role in the pathophysiology of sepsis in burned patients. In addition, a low secondary TGF-beta-1 response and a lack and/or delay in the increase of circulating IL-10 in the non-survivors may all contribute to the pathophysiology of septic death in burned patients.

Impairment of splenic B and T lymphocytes in the early period after severe thermal injury: immunohistochemical and electron microscopic analysis

Immunocompetent cells, such as lymphocytes and macrophages are easily damaged after severe thermal injury. In the present study, we investigated structural changes in splenic lymphocytes in the early period after a full skin thickness burn of 30% of the body surface area in rats. At 2h after thermal injury, numerous B lymphocytes had accumulated in the markedly expanded marginal zone of the splenic white pulp. Electron microscopy showed a small number of apoptotic cells in the marginal zone of the white pulp. After 5h, B lymphocytes in the marginal zone as well as in the lymphoid sheath and follicles were markedly decreased in number with an increase of tingible bodies and tingible body macrophages. The number of apoptotic cells had increased not only in the marginal zone, but also in the lymphoid sheath and follicles. After 12h, the splenic white pulp became atrophic with the appearance of a small number of large blastic cells and mitotic figures. After 24h, the splenic white pulp was still atrophic with a decrease in the number of lymphocytes, especially B lymphocytes. On the other hand, the large blastic cells and mitotic figures increased in number. Apoptotic cells decreased in number in the white pulp. After 48h, the lymph follicles were slightly enlarged and a small germinal centre occasionally appeared. A small number of T lymphocytes were observed in the splenic white pulp of the normal rats. However, the T lymphocytes almost disappeared shortly after thermal injury. A recovery in T cell number was observed only after 48h. These findings indicate that severe impairment of both B and T lymphocytes, circulating and in the lymphoid organs, occurs shortly after thermal injury and continues for several days. This severe damage to the lymphocytes is considered to be closely related to severe immune suppression after thermal injury.

Effects of burn with and without Escherichia coli infection in rats on intestinal vs. splenic T-cell responses

OBJECTIVE

To evaluate the effect of burn injury with and without an Escherichia coliseptic complication on T-cell proliferation, interleukin-2 production, and Ca(2+) signaling responses in intestinal Peyer's patch and splenic T cells.

DESIGN

Prospective, randomized, sham-controlled animal study.

SETTING

University medical center research laboratory.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTIONS

Rats were subjected to a 30% total body surface area, full skin thickness burn. Infection in rats was induced via intraperitoneal inoculation of E. coli, 10(9) colony forming units/kg, with or without a prior burn.

MEASUREMENTS AND MAIN RESULTS

Rat Peyer's patch and splenic T lymphocytes were isolated by using a nylon wool cell purification protocol. T-cell proliferation, interleukin-2 production, and Ca(2+) signaling responses were measured after stimulation of cells with the mitogen, concanavalin A. T-cell proliferation was determined by measuring incorporation of (3)H-thymidine into T-cell cultures. Interleukin-2 production by T-cell cultures was measured by using enzyme-linked immunosorbent assay. Intracellular T-cell Ca2(+ )concentration, [Ca(2+)](i), was measured by the use of Ca(2+)-specific fluorescent label, fura-2, and its fluorometric quantification. [Ca(2+)](i) was also evaluated by the use of digital video imaging of fura-2 loaded individual T cells. T-cell proliferation and interleukin-2 production were suppressed substantially in both Peyer's patch and splenic T cells 3 days after either the initial burn alone or burn followed by the E. coli inoculation at 24 hrs after the initial burn. There seemed to be no demonstrable additive effects of E. coli infection on the effects produced by burn injury alone. The T-cell proliferation and interleukin-2 production suppressions with burn or burn-plus-infection insults were correlated with attenuated Ca(2+) signaling. E. coli infection alone suppressed T-cell proliferation in Peyer's patch but not in splenic T cells at 2 days postbacterial inoculation; E. coli infection had no effect on Peyer's patch or splenic T cells at 1 day postinjury. On the other hand, burn injury alone caused a substantial T-cell proliferative suppression at 2 days postburn in both Peyer's patch and splenic cells and a significant suppression in T-cell proliferation on day 1 postburn in Peyer's patch but not in the spleen.

CONCLUSION

An initial burn injury suppressed T-cell proliferation at a level that it would not be further affected by a subsequent infection even if the infection by itself has the potential of suppressing T-cell proliferation. An earlier onset of T-cell suppression in Peyer's patch cells than in the spleen with burn could be attributable to an initial hypoperfusion-related intestinal mucosal tissue injury. Overall, our study supports the concept that burn injury per se can significantly suppress T-cell mediated immunity and that the intestine is an early tissue site of such suppression.

Thermal injury effects on intestinal crypt cell proliferation and death are cell position dependent

We examined the effects of thermal injury on intestinal epithelial cell proliferation and death. We recorded histologically identifiable mitotic and apoptotic crypt cells in relation to cell position after a 60% full thickness cutaneous thermal injury in the rat. The injury significantly reduced mitosis (0.53 +/- 0.11 vs. 1. 50 +/- 0.70, P < 0.05) at cell positions 4-6, stem cells, 6 h after injury. A similar reduction in mitosis (1.13 +/- 0.59 vs. 3.50 +/- 0. 80, P < 0.05) was observed at higher cell positions 7-9 12 h after injury, indicating a positional cell shift. In addition, a significant increase in the number of apoptotic bodies occurred at cell positions 7-9 (2.32 +/- 0.87 vs. 0.13 +/- 0.22, P < 0.05) and 10-12 (2.2 +/- 0.12 vs. 0.00, P < 0.05) 6 h after injury. Thermal injury-induced alterations in mitotic and apoptotic activities were transient since crypts recovered with a moderate increase in mitotic activity 24 h after injury. In control and thermal-injury rats 24 h after injury, crypt cell mitosis and apoptosis did not differ significantly. This demonstrates that cutaneous thermal injury causes a transient suppression of mitosis as well as induction of apoptosis in a cell position-dependent manner in the small intestinal crypt.