Caspase inhibition reduces cardiac myocyte dyshomeostasis and improves cardiac contractile function after major burn injury

Acute kidney injury in patients with burns

Burn injury is associated with a high risk of acute kidney injury (AKI) with a prevalence of AKI among patients with burns of 9-50%. Despite an improvement in burn injury survival in the past decade, AKI in patients with burns is associated with an extremely poor short-term and long-term prognosis, with a mortality of >80% among those with severe AKI. Factors that contribute to the development of AKI in patients with burns include haemodynamic alterations, burn-induced systemic inflammation and apoptosis, haemolysis, rhabdomyolysis, smoke inhalation injury, drug nephrotoxicity and sepsis. Early and late AKI after burn injury differ in their aetiologies and outcomes. Sepsis is the main driver of late AKI in patients with burns and late AKI has been associated with higher mortality than early AKI. Prevention of early AKI involves correction of hypovolaemia and avoidance of nephrotoxic drugs (for example, hydroxocobalamin), whereas prevention of late AKI involves prevention and early recognition of sepsis as well as avoidance of nephrotoxins. Treatment of AKI in patients with burns remains supportive, including prevention of fluid overload, treatment of electrolyte disturbance and use of kidney replacement therapy when indicated.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

Pathological Responses of Cardiac Mitochondria to Burn Trauma

Despite advances in treatment and care, burn trauma remains the fourth most common type of traumatic injury. Burn-induced cardiac failure is a key factor for patient mortality, especially during the initial post-burn period (the first 24 to 48 h). Mitochondria, among the most important subcellular organelles in cardiomyocytes, are a central player in determining the severity of myocardial damage. Defects in mitochondrial function and structure are involved in pathogenesis of numerous myocardial injuries and cardiovascular diseases. In this article, we comprehensively review the current findings on cardiac mitochondrial pathological changes and summarize burn-impaired mitochondrial respiration capacity and energy supply, induced mitochondrial oxidative stress, and increased cell death. The molecular mechanisms underlying these alterations are discussed, along with the possible influence of other biological variables. We hope this review will provide useful information to explore potential therapeutic approaches that target mitochondria for cardiac protection following burn injury.

Burn-induced reductions in mitochondrial abundance and efficiency are more pronounced with small volumes of colloids in swine

Severe burn injury results in systemic disruption of metabolic regulations and impaired cardiac function. Restoration of hemodynamic homeostasis utilizing intravenous (IV) fluids is critical for acute care of the burn victim. However, the effects of burns and resuscitation on cardiomyocyte mitochondria are currently unknown. The purpose of this study is to determine cardiac mitochondrial function in a swine burn model with subsequent resuscitation using either crystalloids or colloids. Anesthetized Yorkshire swine (n = 23) sustained 40% total body surface area burns and received IV crystalloids (n = 11) or colloids (n = 12) after recovery from anesthesia. Non-burned swine served as controls (n = 9). After euthanasia at 48 h, heart tissues were harvested, permeabilized, and analyzed by high-resolution respirometry. Citrate synthase (CS) activity was measured, and Western blots were performed to quantify proteins associated with mitochondrial fusion (OPA1), fission (FIS1), and mitophagy (PINK1). There were no differences in state 2 respiration or maximal oxidative phosphorylation. Coupled complex 1 respiration decreased, while uncoupled state 4_O and complex II increased significantly due to burn injury, particularly in animals receiving colloids (P < 0.05). CS activity and electron transfer coupling efficiency were significantly lower in burned animals, particularly with colloid treatment (P < 0.05). Protein analysis revealed increased FIS1 but no differences in mitophagy in cardiac tissue from colloid-treated compared with crystalloid-treated swine. Taken together, severe burns alter mitochondrial respiration in heart tissue, which may be exacerbated by early IV resuscitation with colloids. Early IV burn resuscitation with colloids may require close hemodynamic observation. Mitochondrial stabilizing agents incorporated into resuscitation fluids may help the hemodynamic response to burn injury.

Serum Level of Musclin Is Elevated Following Severe Burn

Muscle wasting induced by severe burn worsens clinical outcomes is associated with hyperglycemia. A novel muscle-specific secretory factor, musclin, was reported to regulate glucose metabolism with a homologous sequence of natriuretic peptides. The purpose of the study was to investigate musclin expression in response to burn injury in both human and animal models. Serum was collected from 13 adult burn patients and circulating levels of musclin protein were measured via elisa. The cytokine profile was measured by Bio-Plex multiple immunoassay. Following the clinical study, we used a burn rat model with 40% TBSA to study the time course of musclin expression till day 14. Rat serum and muscle tissue sample were harvested. Finally, an in vitro study was applied to investigate whether the muscle cell C2C12 myoblast expressed musclin under 10% burn serum stimulation. Pearson analysis showed that there was a significant positive correlation of musclin expression to total body surface area of burn in patients (P &= .038). Musclin expression was significantly positively correlated with IL-4, IL-7, IL-12, and IL-13 in burn patients’ serum (P < .05). In the animal study, we found that the musclin level evaluated at 6 hours and 1 day in burn rat serum (P < .05). In vitro, musclin mRNA expression significantly increased with burn serum stimulation at 24 hours (P < .05). In conclusion, serum level of musclin elevated both in human patients and burn animals; musclin was correlated with the severity of burn injury as well as with an elevated cytokine profile in patients; burn serum-stimulated musclin expression in vitro further identified the resource of musclin expression after burn.

The independence of and associations among apoptosis, autophagy, and necrosis

Cell death is an essential biological process for physiological growth and development. Three classical forms of cell death-apoptosis, autophagy, and necrosis-display distinct morphological features by activating specific signaling pathways. With recent research advances, we have started to appreciate that these cell death processes can cross-talk through interconnecting, even overlapping, signaling pathways, and the final cell fate is the result of the interplay of different cell death programs. This review provides an insight into the independence of and associations among these three types of cell death and explores the significance of cell death under the specific conditions of human diseases, particularly neurodegenerative diseases and cancer.

Burn Serum Stimulates Myoblast Cell Death Associated with IL-6-Induced Mitochondrial Fragmentation

BACKGROUND

Burn patients suffer muscle mass loss associated with hyperinflammation and hypercatabolism. The mitochondria are affected by this metabolic alteration. Mitochondrial fission activates a caspase cascade that ultimately leads to cell death. We postulate that burn-induced muscle loss is associated with increased mitochondrial fission and subsequent functional impairment. Further, we investigated whether the cytokine IL-6 plays a major role in mitochondrial fission-associated cell death after burn.

METHODS

Murine myoblast C2C12 cells were treated with 10% serum isolated either from control rats or 40% total body surface area burned rats. Mitochondria were labeled with MitoTracker Green for live cell images. Mitochondrial function was assessed with an Enzo Mito-ID membrane potential cytotoxicity kit. Protein signals were detected by Western blot analysis. Moreover, recombinant IL-6 was applied to stimulate C2C12 to differentiate the role of cytokine IL-6; lastly, we treated burn serum-stimulated cells with IL-6 antibodies.

RESULTS

Caspase 3 activity increased in C2C12 cells with burn serum stimulation, suggesting increased cell death in skeletal muscle after burn. Mitochondrial morphology shortened and mitochondrial membrane potential decreased in cells treated with burn serum. Western blot data showed that mitofusion-1 expression significantly decreased in burn serum-treated cells, supporting the morphologic observation of mitochondrial fission. Mitochondrial fragmentation increased with IL-6 stimulation, and IL-6 antibody decreased caspase 3 activity and mitochondrial membrane potential improved in burn serum-stimulated cells.

CONCLUSION

Burn serum caused muscle cell death associated with increased mitochondrial fission and functional impairment. This alteration was alleviated with IL-6 antibody treatment, suggesting the cytokine plays a role in mitochondrial changes in muscle after systemic injury.

Association of soluble apoptotic markers with impaired left ventricular deformation in patients with rheumatoid arthritis. Effects of inhibition of interleukin-1 activity by anakinra

Myocardial function is impaired in rheumatoid arthritis (RA). Inhibition of interleukin (IL)-1 activity reduces experimental myocardial infarction by limiting apoptosis. We investigated whether a) soluble apoptotic markers are related with impaired left ventricular (LV) performance and b) treatment with anakinra, an IL-1 receptor antagonist, reduces apoptotic markers leading to improved LV performance in RA. We studied 46 RA patients. In an acute, double-blind cross-over trial, 23 patients were randomised to a single injection of anakinra or placebo and after 48 hours (h) to the alternative treatment. In a chronic trial, 23 patients who received anakinra for 30 days were compared with 23 patients who received prednisolone. At baseline, 3 h and 30 days after treatment, we measured circulating IL-1β, tumour necrosis factor (TNF)-α, Fas, Fas-ligand and caspase-9 to assess apoptosis. At baseline and 30 days after treatment, we assessed LV longitudinal strain, strain rate and E/Em ratio using 2D-speckle tracking and tissue Doppler echocardiography. At baseline, increased apoptotic markers were related with reduced LongSRS and increased E/Em (p<0.05). After 3 h and 30 days of anakinra, there was a reduction in Fas (median 481 vs. 364 vs. 301 pg/ml), Fasligand (median 289 vs. 221 vs. 190 pg/ml), caspase-9 (median 1.90 vs. 1.40 vs. 1.07 ng/ml), TNF-α and IL-1β (p<0.05 for all comparisons). E/Em, LongS and LongSRS were improved after anakinra (p<0.01) and their percent changes were related with the corresponding changes of Fas and caspase-9 (p<0.05). No changes of the examined parameters were observed after prednisolone. In conclusion, inhibition of IL-1 activity by anakinra reduces apoptotic markers leading to improved LV performance in RA.

Cardiovascular Dysfunction Following Burn Injury: What We Have Learned from Rat and Mouse Models

Severe burn profoundly affects organs both proximal and distal to the actual burn site. Cardiovascular dysfunction is a well-documented phenomenon that increases morbidity and mortality following a massive thermal trauma. Beginning immediately post-burn, during the ebb phase, cardiac function is severely depressed. By 48 h post-injury, cardiac function rebounds and the post-burn myocardium becomes tachycardic and hyperinflammatory. While current clinical trials are investigating a variety of drugs targeted at reducing aspects of the post-burn hypermetabolic response such as heart rate and cardiac work, there is still a paucity of knowledge regarding the underlying mechanisms that induce cardiac dysfunction in the severely burned. There are many animal models of burn injury, from rodents, to sheep or swine, but the majority of burn related cardiovascular investigations have occurred in rat and mouse models. This literature review consolidates the data supporting the prevalent role that β-adrenergic receptors play in mediating post-burn cardiac dysfunction and the idea that pharmacological modulation of this receptor family is a viable therapeutic target for resolving burn-induced cardiac deficits.

Inhibition of Apoptosis and Efficacy of Pan Caspase Inhibitor, Q-VD-OPh, in Models of Human Disease

Apoptosis is physiological cell death required for the cellular maintenance of homeostasis, and caspases play a major role in the execution of this process. Numerous disorders occur when levels of apoptosis within an organism are excessive, and several studies have explored the possibility of using caspase inhibitors to prevent these disorders. Q-VD-OPh (quinolyl-valyl-O-methylaspartyl-[2,6-difluorophenoxy]-methyl ketone), a novel pan caspase inhibitor, has been used because of its efficacy to inhibit apoptosis at low concentrations, its ability to cross the blood-brain barrier, as well as being nontoxic in vivo. This review examines Q-VD-OPh's ability to inhibit apoptosis in several animal models of human disease.

Severe burn injury, burn shock, and smoke inhalation injury in small animals. Part 1: burn classification and pathophysiology

OBJECTIVE

To review the literature related to severe burn injury (SBI), burn shock, and smoke inhalation injury in domestic animals. Current animal- and human-based research and literature were evaluated to provide an overview of thermal burn classification and the pathophysiology of burn shock and smoke inhalation injury.

ETIOLOGY

Severe burn injury, burn shock, and smoke inhalation injury may be encountered as a result of thermal injury, radiation injury, chemical injury, or electrical injury.

DIAGNOSIS

Burns can be subdivided based on the amount of total body surface area (TBSA) involved and the depth of the burn. Local burn injuries involve <20% of the TBSA whereas SBI involves >20-30% of the TBSA. The modern burn classification system classifies burns by increasing depth: superficial, superficial partial-thickness, deep partial-thickness, and full-thickness.

SUMMARY

Local burn injury rarely leads to systemic illness whereas SBI leads to significant metabolic derangements that require immediate and intensive management. SBI results in a unique derangement of cardiovascular dysfunction known as "burn shock." The physiologic changes that occur with SBI can be divided into 2 distinct phases; the resuscitation phase and the hyperdynamic hypermetabolic phase. The resuscitation phase occurs immediately following SBI and lasts for approximately 24-72 hours. This period of hemodynamic instability is characterized by the release of inflammatory mediators, increased vascular permeability, reduced cardiac output, and edema formation. The hyperdynamic hypermetabolic phase begins approximately 3-5 days after injury. This phase is characterized by hyperdynamic circulation and an increased metabolic rate that can persist up to 24 months post burn injury in people.

Treatment with gelsolin reduces brain inflammation and apoptotic signaling in mice following thermal injury

Background

Burn survivors develop long-term cognitive impairment with increased inflammation and apoptosis in the brain. Gelsolin, an actin-binding protein with capping and severing activities, plays a crucial role in the septic response. We investigated if gelsolin infusion could attenuate neural damage in burned mice.

Methods

Mice with 15% total body surface area burns were injected intravenously with bovine serum albumin as placebo (2 mg/kg), or with low (2 mg/kg) or high doses (20 mg/kg) of gelsolin. Samples were harvested at 8, 24, 48 and 72 hours postburn. The immune function of splenic T cells was analyzed. Cerebral pathology was examined by hematoxylin/eosin staining, while activated glial cells and infiltrating leukocytes were detected by immunohistochemistry. Cerebral cytokine mRNAs were further assessed by quantitative real-time PCR, while apoptosis was evaluated by caspase-3. Neural damage was determined using enzyme-linked immunosorbent assay of neuron-specific enolase (NSE) and soluble protein-100 (S-100). Finally, cerebral phospho-ERK expression was measured by western blot.

Results

Gelsolin significantly improved the outcomes of mice following major burns in a dose-dependent manner. The survival rate was improved by high dose gelsolin treatment compared with the placebo group (56.67% vs. 30%). Although there was no significant improvement in outcome in mice receiving low dose gelsolin (30%), survival time was prolonged against the placebo control (43.1 ± 4.5 h vs. 35.5 ± 5.0 h; P < 0.05). Burn-induced T cell suppression was greatly alleviated by high dose gelsolin treatment. Concurrently, cerebral abnormalities were greatly ameliorated as shown by reduced NSE and S-100 content of brain, decreased cytokine mRNA expressions, suppressed microglial activation, and enhanced infiltration of CD11b+ and CD45+ cells into the brain. Furthermore, the elevated caspase-3 activity seen following burn injury was remarkably reduced by high dose gelsolin treatment along with down-regulation of phospho-ERK expression.

Conclusion

Exogenous gelsolin infusion improves survival of mice following major burn injury by partially attenuating inflammation and apoptosis in brain, and by enhancing peripheral T lymphocyte function as well. These data suggest a novel and effective strategy to combat excessive neuroinflammation and to preserve cognition in the setting of major burns.

Caspase-dependent protein phosphatase 2A activation contributes to endotoxin-induced cardiomyocyte contractile dysfunction

OBJECTIVE

Several studies report calcium mishandling, sarcomere disarray, and caspase activation during heart failure. Although active caspases have been shown to cleave myofibrillar proteins, little is known regarding their effects on calcium handling proteins. Therefore, we aimed to explore how endotoxin-induced caspase activation disrupts intracellular calcium regulation.

DESIGN

Randomized controlled trial.

SETTING

Small animal research laboratory.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTIONS

Sepsis was induced by injection of endotoxin (10 mg/kg, intravenously). Caspase inhibition was achieved by coinjection with zVAD.fmk (3 mg/kg, intravenously). We first isolated adult rat ventricular myocytes from control, endotoxin, and (endotoxin + zVAD)-treated rats to characterize contractile parameters and cellular calcium homeostasis. Underlying molecular mechanisms responsible for calcium mishandling were explored on sarcoplasmic reticulum vesicles and mitochondria prepared from treated animals. All experiments were performed 4 hrs postendotoxin treatment.

MEASUREMENTS AND MAIN RESULTS

zVAD normalized reductions in fractional cell shortening and relaxation rate triggered by endotoxin treatment. Both sarco-/endoplasmic reticulum Ca-ATPase and mitochondria-dependent calcium uptakes were impaired after endotoxin treatment and prevented when myocytes were isolated from zVAD-treated endotoxinic rat hearts. zVAD blocked endotoxin-induced phospholamban dephosphorylation, protein phosphatase 2A activation, and mitochondrial calcium retention capacity reduction. To strengthen these results, control sarcoplasmic reticulum vesicles and mitochondria were incubated with active recombinant caspase-3. Although no effects were observed on mitochondria, caspase-3 directly exerts detrimental effects on sarcoplasmic reticulum calcium uptake capacity by activating protein phosphatase 2A, leading to phospholamban dephosphorylation.

CONCLUSIONS

Caspase inhibition protects from endotoxin-induced sarcoplasmic reticulum calcium uptake capacity reduction and mitochondrial dysfunction.

Caspase-3 knock-down reverses contractile dysfunction induced by sepsis in adult rat ventricular myocytes

BACKGROUND AND PURPOSE

The present study tested the hypothesis that selective caspase-3 (C-3) knock-out would regulate the contractile actions of noradrenaline (NA) in the dysfunction of adult rat ventricular myocytes (ARVMs) induced by sepsis. Here, we have studied the contractile response of ARVMs, transfected with C-3 small interfering RNA (C-3 siRNA), to NA.

EXPERIMENTAL APPROACH

Single ARVMs were isolated from the hearts of male Sprague-Dawley rats 3 days after induction of sepsis, and from sham-treated rats. The sham and septic ARVMs were treated with NA (10 microM) alone or after transfection with C-3 siRNA or non-silencing RNA (2 microM). Mechanical properties were measured digitally, and immunoblotting and immunocytochemical analyses were carried out.

KEY RESULTS

The NA-induced increase in peak shortening (PS) was less in septic ARVMs and transfection with C-3 siRNA produced a significant increase in this PS. Immunocytochemical and immunoblot analyses revealed that NA exacerbated sepsis-induced up-regulation of C-3. Transfection of septic ARVMs with C-3 siRNA exhibited a decreased expression of C-3 fluorescence after NA. In septic ARVMs, we also observed a down-regulation of contractile proteins (alpha-actin, myosin light chain-1 and tropomyosin) along with DNA damage. Transfection of septic ARVMs with C-3 siRNA produced an increase in the expression of contractile proteins, and a decrease in DNA damage.

CONCLUSIONS AND IMPLICATIONS

These data suggest that C-3 knock-down improved the loss of contractile response to NA in septic ARVMs, suggesting that C-3 regulated contractile dysfunction induced by sepsis in ARVMs.

Estrogen treatment following severe burn injury reduces brain inflammation and apoptotic signaling

Background

Patients with severe burn injury experience a rapid elevation in multiple circulating pro-inflammatory cytokines, with the levels correlating with both injury severity and outcome. Accumulations of these cytokines in animal models have been observed in remote organs, however data are lacking regarding early brain cytokine levels following burn injury, and the effects of estradiol on these levels. Using an experimental animal model, we studied the acute effects of a full-thickness third degree burn on brain levels of TNF-α, IL-1β, and IL-6 and the protective effects of acute estrogen treatment on these levels. Additionally, the acute administration of estrogen on regulation of inflammatory and apoptotic events in the brain following severe burn injury were studied through measuring the levels of phospho-ERK, phospho-Akt, active caspase-3, and PARP cleavage in the placebo and estrogen treated groups.

Methods

In this study, 149 adult Sprague-Dawley male rats received 3rd degree 40% total body surface area (TBSA) burns. Fifteen minutes following burn injury, the animals received a subcutaneous injection of either placebo (n = 72) or 17 beta-estradiol (n = 72). Brains were harvested at 0.5, 1, 2, 4, 6, 8, 12, 18, and 24 hours after injury from the control (n = 5), placebo (n = 8/time point), and estrogen treated animals (n = 8/time point). The brain cytokine levels were measured using the ELISA method. In addition, we assessed the levels of phosphorylated-ERK, phosphorylated-Akt, active caspase-3, and the levels of cleaved PARP at the 24 hour time-point using Western blot analysis.

Results

In burned rats, 17 beta-estradiol significantly decreased the levels of brain tissue TNF-α (~25%), IL-1β (~60%), and IL-6 (~90%) when compared to the placebo group. In addition, we determined that in the estrogen-treated rats there was an increase in the levels of phospho-ERK (p < 0.01) and Akt (p < 0.05) at the 24 hour time-point, and that 17 beta-estradiol blocked the activation of caspase-3 (p < 0.01) and subsequent cleavage of PARP (p < 0.05).

Conclusion

Following severe burn injury, estrogens decrease both brain inflammation and the activation of apoptosis, represented by an increase in the levels of phospho-Akt and inhibition of caspase-3 activation and PARP cleavage. Results from these studies will help further our understanding of how estrogens protect the brain following burn injury, and may provide a novel, safe, and effective clinical treatment to combat remote secondary burn injury in the brain and to preserve cognition.

Contractile response of norepinephrine is modulated by caspase-3 in adult rat ventricular myocytes isolated from septic rat heart

Sepsis accounts for 50% of intensive care unit deaths due to cardiac dysfunction. The cellular mechanisms following norepinephrine (NE) during sepsis are undefined. Using a septic adult rat ventricular myocyte (ARVM) paradigm, we examined the molecular mechanism responsible for the blunted contractile response of NE. We tested the hypothesis that NE-induced increases in active caspase-3 contribute to sepsis-induced ARVM contractile dysfunction. Single ARVMs were isolated from hearts harvested from sham and septic male rats. The contractile properties and expression of caspase-3 cascade proteins were determined in ARVMs treated with NE with and without QVD-OPH, prazosin and atenolol to characterize the effect of NE on their mechanical properties. Septic ARVMs exhibited a significant decrease in peak shortening (PS) compared to sham ARVMs. The effect of NE on the PS of the sham ARVMs was more pronounced compared to the septic ARVMs, suggesting a blunted contractile response of NE. NE in the presence of QVD-OPH ameliorated the sepsis-induced decrease in PS at 18h but not at 1h, while the effect of NE on sepsis-induced contractile response remained unaffected at 18h by prazosin and atenolol. An up-regulated expression of caspase-3 in NE-treated septic ARVMs was reversed by QVD-OPH, as seen by the increased number of septic ARVMs exhibiting caspase-3 fluorescence. Transfection of ARVMs using caspase-3 siRNA blocked sepsis-induced up-regulation of caspase-3 and increased PS following NE treatment. These data suggest that caspase-3 inhibition ameliorated sepsis-induced decreased ARVM contractility and blocked the blunted contractile response of NE.

HSP70 inhibits burn serum-induced apoptosis of cardiomyocytes via mitochondrial and membrane death receptor pathways

The objective is to determine if Hsp70 is involved in the mechanism by which serum from burn rats induces apoptosis of cardiomyocytes. Cardiomyocytes in primary culture were assigned to the following groups: normal controls, normal rat serum, burn serum, burn serum plus empty vector control, and burn serum plus Hsp70 transfection. Each group, except normal controls, was cultured with the corresponding serum for 2 hours. The empty vector controls and the Hsp70 groups were transfected, respectively, with the empty vector or pcDNA3.1-Hsp70 recombinant plasmid 36 hours previously. Hsp70 protein levels were assessed by Western blot. Apoptotic cells were counted after Hoechst 33258 staining. Apoptosis of cardiomyocytes was also detected by the presence of "ladder" bands in agarose gels following electrophoresis of extracted DNA. Activation of caspase-3, -8, and -9 and Bid cleavage were assessed by Western blot. Hsp70 overexpression inhibited burn serum-induced apoptosis of cardiomyocytes; and burn serum-induced activation of caspases-3, -8, and -9; and Bid cleavage into tBid. Hsp70 inhibits burn serum-induced apoptosis by interfering with death receptor and mitochondrial pathways.

Apoptosis in cardiac myocytes during the early stage after severe burn

BACKGROUND

Cardiac dysfunction after severe burn is associated with postburn myocardial injury. We hypothesize that myocyte apoptosis is triggered and presented as the pathologic basis of postburn myocardial injury during the early stage after severe burn, and that apoptosis may be related to inflammatory responses in the postburn myocardium.

METHODS

Rats with 40% total body surface area full-thickness burn were used. The following functions were measured at several time points after the burn injury: myocyte apoptosis (TUNEL staining, DNA ladder, and caspase-3 activity assay); mRNA levels of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (reverse transcriptase-polymerase chain reaction [RT-PCR]); activities of myeloperoxidase and p38 mitogen activated protein (MAP) kinase (Western blots); and left cardiac function.

RESULTS

TUNEL positive myocytes appeared as early as 6-hour and their numbers showed further increases at 12-hour and 24-hour postburn; DNA fragmentation was clearly observed, and caspase-3 activity was significantly increased in the myocardium after burn. Infiltration of neutrophils, evidenced by the levels of myeloperoxidase activity, expression of TNF-alpha, and p38 MAP kinase activity in the heart, were all significantly increased within 24-hour after burn. Cardiac function was decreased after burn, which approximately paralleled the increased amount of cardiac apoptosis.

CONCLUSION

These results demonstrate that cardiomyocyte apoptosis progressively develops during the early stage after severe burn, which may in part contribute to burn-induced cardiac dysfunction. Myocardial inflammatory responses, evidenced by the increased infiltration of neutrophils, as well as production of TNF-alpha probably because of the activation of p38 MAP kinase, may be involved in burn-induced cardiomyocyte apoptosis.