Cardiac effects of burn injury complicated by aspiration pneumonia-induced sepsis

Cardioprotective Effect of Tangeretin by Inhibiting PTEN/AKT/mTOR Axis in Experimental Sepsis-Induced Myocardial Dysfunction

Sepsis aggregates undesirable immune response causing depression of ventricular myocardium and diastolic dysfunction. This present study examined the effect of a plant-derived flavone tangeretin (TG) on autophagy and reduction in myocardial dysfunction. The sepsis was induced by cecum ligation and puncture (CLP) in male Sprague-Dawley rats. Abnormal changes were seen in the heart after the sepsis induction. These abnormalities were analyzed based on the cardiac markers, namely Cardiac myosin light chain-1 (cMLC1) and Cardiac troponin I (cTnl), echocardiography, and plasma parameters, like Lactate dehydrogenase (LDH) and Creatinine kinase (CK). Microanatomy of the heart was studied using hematoxylin and eosin stained histopathological samples of cardiac tissue. Western blot technique was used to detect the nature and extent of protein with the amount of a specific RNA (gene expression) in the cardiac homogenate. Oxidative damage was analyzed using redox marker, reduced glutathione. This study successfully showed that TG attenuated sepsis-induced myocardial dysfunction by inhibiting myocardial autophagy via silencing the Phosphatase and tensin homolog (PTEN) expression and acting on the AKT/mTOR pathway. The present findings supported that TG is a novel cardioprotective therapeutic target for sepsis induced myocardial dysfunction.

Cardiac Structure and Function in Well-Healed Burn Survivors

Long-term burn survivors have reduced aerobic capacity, placing them at increased risk for cardiovascular disease, morbidity, and mortality. However, the exact mechanism contributing to a reduced aerobic capacity remains incompletely understood, but may be related to adverse cardiovascular remodeling. Therefore, it was hypothesized that well-healed burn survivors would exhibit adverse left ventricular (LV) remodeling and impaired LV function. To test this hypothesis, 22 well-healed moderately burned individuals (age: 41 ± 14 years; BMI: 27.7 ± 5.4 kg/m2; male/female: 12/10; extent of burn: 37 ± 12 %BSA), 11 well-healed severely burned individuals (age: 43 ± 12 years; BMI: 29.5 ± 5.8 kg/m2; male/female: 8/3; extent of burn: 73 ± 11 %BSA), and 12 healthy, age-matched controls (age: 34 ± 9 years; BMI: 28.6 ± 5.2 kg/m2; male/female: 5/7) were enrolled in the study. All subjects were sedentary, performing less than 30 minutes of aerobic exercise per day, 3 days per week. LV morphology and function were assessed via cardiac magnetic resonance imaging. In contrast to the hypothesis, neither the presence nor severity of burn injury adversely affected LV morphology or function, when compared with equally sedentary nonburned controls. However, of note, LV mass of all three groups was in the lowest 5th percentile compared with normative values. Finally, group differences in LV morphology were largely explained by differences in aerobic capacity. Taken together, these data suggest a prior burn injury itself does not result in pathological remodeling of the LV and support a role for aerobic exercise training to improve cardiac function.

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.

Mitochondrial ROS Induces Cardiac Inflammation via a Pathway through mtDNA Damage in a Pneumonia-Related Sepsis Model

We have previously shown that mitochondria-targeted vitamin E (Mito-Vit-E), a mtROS specific antioxidant, improves cardiac performance and attenuates inflammation in a pneumonia-related sepsis model. In this study, we applied the same approaches to decipher the signaling pathway(s) of mtROS-dependent cardiac inflammation after sepsis. Sepsis was induced in Sprague Dawley rats by intratracheal injection of S. pneumoniae. Mito-Vit-E, vitamin E or vehicle was administered 30 minutes later. In myocardium 24 hours post-inoculation, Mito-Vit-E, but not vitamin E, significantly protected mtDNA integrity and decreased mtDNA damage. Mito-Vit-E alleviated sepsis-induced reduction in mitochondria-localized DNA repair enzymes including DNA polymerase γ, AP endonuclease, 8-oxoguanine glycosylase, and uracil-DNA glycosylase. Mito-Vit-E dramatically improved metabolism and membrane integrity in mitochondria, suppressed leakage of mtDNA into the cytoplasm, inhibited up-regulation of Toll-like receptor 9 (TLR9) pathway factors MYD88 and RAGE, and limited RAGE interaction with its ligand TFAM in septic hearts. Mito-Vit-E also deactivated NF-κB and caspase 1, reduced expression of the essential inflammasome component ASC, and decreased inflammatory cytokine IL–1β. In vitro, both Mito-Vit-E and TLR9 inhibitor OND-I suppressed LPS-induced up-regulation in MYD88, RAGE, ASC, active caspase 1, and IL–1β in cardiomyocytes. Since free mtDNA escaped from damaged mitochondria function as a type of DAMPs to stimulate inflammation through TLR9, these data together suggest that sepsis-induced cardiac inflammation is mediated, at least partially, through mtDNA-TLR9-RAGE. At last, Mito-Vit-E reduced the circulation of myocardial injury marker troponin-I, diminished apoptosis and amended morphology in septic hearts, suggesting that mitochondria-targeted antioxidants are a potential cardioprotective approach for sepsis.

Sepsis-induced Cardiac Mitochondrial Damage and Potential Therapeutic Interventions in the Elderly

The incidence of sepsis and its attendant mortality risk are significantly increased with aging. Thus, severe sepsis in the elderly is likely to become an emerging concern in critical care units. Cardiac dysfunction is an important component of multi-organ failure after sepsis. In our laboratory, utilizing a pneumonia-related sepsis animal model, our research has been focused on the mechanisms underlying sepsis-induced cardiac failure. In this review, based on findings from others and ours, we discussed age-dependent decay in mitochondria and the role of mitochondrial reactive oxygen species (mtROS) in sepsis-induced cardiac inflammation and autophagy. Our recent discovery of a potential signal transduction pathway that triggers myocardial mitochondrial damage is also discussed. Because of the significance of mitochondria damage in the aging process and in sepsis pathogenesis, we hypothesize that specific enhancing mitochondrial antioxidant defense by mitochondria-targeted antioxidants (MTAs) may provide important therapeutic potential in treating elder sepsis patients. In this review, we summarized the categories of currently published MTA molecules and the results of preclinical evaluation of MTAs in sepsis and aging models.

Sepsis-induced cardiac mitochondrial dysfunction involves altered mitochondrial-localization of tyrosine kinase Src and tyrosine phosphatase SHP2

Our previous research demonstrated that sepsis produces mitochondrial dysfunction with increased mitochondrial oxidative stress in the heart. The present study investigated the role of mitochondria-localized signaling molecules, tyrosine kinase Src and tyrosine phosphatase SHP2, in sepsis-induced cardiac mitochondrial dysfunction using a rat pneumonia-related sepsis model. SD rats were given an intratracheal injection of Streptococcus pneumoniae, 4×10(6) CFU per rat, (or vehicle for shams); heart tissues were then harvested and subcellular fractions were prepared. By Western blot, we detected a gradual and significant decrease in Src and an increase in SHP2 in cardiac mitochondria within 24 hours post-inoculation. Furthermore, at 24 hours post-inoculation, sepsis caused a near 70% reduction in tyrosine phosphorylation of all cardiac mitochondrial proteins. Decreased tyrosine phosphorylation of certain mitochondrial structural proteins (porin, cyclophilin D and cytochrome C) and functional proteins (complex II subunit 30kD and complex I subunit NDUFB8) were evident in the hearts of septic rats. In vitro, pre-treatment of mitochondrial fractions with recombinant active Src kinase elevated OXPHOS complex I and II-III activity, whereas the effect of SHP2 phosphatase was opposite. Neither Src nor SHP2 affected complex IV and V activity under the same conditions. By immunoprecipitation, we showed that Src and SHP2 consistently interacted with complex I and III in the heart, suggesting that complex I and III contain putative substrates of Src and SHP2. In addition, in vitro treatment of mitochondrial fractions with active Src suppressed sepsis-associated mtROS production and protected aconitase activity, an indirect marker of mitochondrial oxidative stress. On the contrary, active SHP2 phosphatase overproduced mtROS and deactivated aconitase under the same in vitro conditions. In conclusion, our data suggest that changes in mitochondria-localized signaling molecules Src and SHP2 constitute a potential signaling pathway to affect mitochondrial dysfunction in the heart during sepsis.

Specific inhibition of mitochondrial oxidative stress suppresses inflammation and improves cardiac function in a rat pneumonia-related sepsis model

Using a mitochondria-targeted vitamin E (Mito-Vit-E) in a rat pneumonia-related sepsis model, we examined the role of mitochondrial reactive oxygen species in sepsis-mediated myocardial inflammation and subsequent cardiac contractile dysfunction. Sepsis was produced in adult male Sprague-Dawley rats via intratracheal injection of S. pneumonia (4 × 10(6) colony formation units per rat). A single dose of Mito-Vit-E, vitamin E, or control vehicle, at 21.5 μmol/kg, was administered 30 min postinoculation. Blood was collected, and heart tissue was harvested at various time points. Mito-Vit-E in vivo distribution was confirmed by mass spectrometry. In cardiac mitochondria, Mito-Vit-E improved total antioxidant capacity and suppressed H(2)O(2) generation, whereas vitamin E offered little effect. In cytosol, both antioxidants decreased H(2)O(2) levels, but only vitamin E strengthened antioxidant capacity. Mito-Vit-E protected mitochondrial structure and function in the heart during sepsis, demonstrated by reduction in lipid and protein oxidation, preservation of mitochondrial membrane integrity, and recovery of respiratory function. While both Mito-Vit-E and vitamin E suppressed sepsis-induced peripheral and myocardial production of proinflammatory cytokines (tumor necrosis factor-α, interleukin-1β, and interleukin-6), Mito-Vit-E exhibited significantly higher efficacy (P < 0.05). Stronger anti-inflammatory action of Mito-Vit-E was further shown by its near-complete inhibition of sepsis-induced myeloperoxidase accumulation in myocardium, suggesting its effect on neutrophil infiltration. Echocardiography analysis indicated that Mito-Vit-E ameliorated cardiac contractility of sepsis animals, shown by improved fractional shortening and ejection fraction. Together, our data suggest that targeted scavenging of mitochondrial reactive oxygen species protects mitochondrial function, attenuates tissue-level inflammation, and improves whole organ activities in the heart during sepsis.

Animal models of external traumatic wound infections

BACKGROUND

Despite advances in traumatic wound care and management, infections remain a leading cause of mortality,morbidity and economic disruption in millions of wound patients around the world. Animal models have become standard tools for studying a wide array of external traumatic wound infections and testing new antimicrobial strategies.

RESULTS

Animal models of external traumatic wound infections reported by different investigators vary in animal species used, microorganism strains, the number of microorganisms applied, the size of the wounds and for burn infections, the length of time the heated object or liquid is in contact with the skin.

METHODS

This review covers experimental infections in animal models of surgical wounds, skin abrasions, burns, lacerations,excisional wounds and open fractures.

CONCLUSIONS

As antibiotic resistance continues to increase,more new antimicrobial approaches are urgently needed.These should be tested using standard protocols for infections in external traumatic wounds in animal models.

Age-dependent differences of interleukin-6 activity in cardiac function after burn complicated by sepsis

Interleukin (IL)-6 is a pleiotropic cytokine that is activated after acute injuries, and plays an important role during aging. We aim to define the role of IL-6 on myocardial dysfunction following a 40% total body surface area burn followed by late (7 days) Streptococcus pneumoniae sepsis (burn plus sepsis) in 2- and 14-month-old wild type and IL-6(-/-) mice. We measured global hemodynamic and cardiac contractile function with left ventricular pressure-volume analysis 24h after sepsis induction, and measured phosphorylated signal transducer and activator of transcription 3 (p-STAT-3), tumor necrosis factor (TNF)-alpha, and IL-1beta in the heart with Western blot analysis. We also measured mRNA expression of IL-6, TNF-alpha, and IL-1beta. Sham injured mice did not manifest any appreciable level of p-STAT-3 or functional deficiencies regardless of age or presence of the IL-6 gene. Burn plus sepsis injury was associated with a significant deterioration of global hemodynamic and cardiac contractile function in WT mice in both age groups. This dysfunction was attenuated by IL-6 deficiency at age 2 months, but accentuated at age 14 months. Aging was associated with an increase in mRNA expression of IL-6 (WT mice), TNF-alpha, and IL-1beta (all mice). At age 14 months, IL-6 deficient mice exhibited a greater TNF-alpha mRNA expression than the wild type mice. We conclude aging is associated with changed cytokine gene transcription, and burn plus sepsis injury further intensifies such gene responses. IL-6 deficiency does not abrogate STAT-3 phosphorylation and it may enhance expression of other inflammatory cytokines. The differential effects of IL-6 deficiency on the cardiac function in young and aging mice cannot be explained by cytokine gene expression alone, and require further studies.

A comparative study of the in vitro permeation characteristic of sulphadiazine across synthetic membranes and eschar tissue

Infections of burn wounds are the source of significant problems in burn patients. Early excision of eschar tissue is an ideal solution to avoid sepsis. When early excision is not feasible, the application of topical antimicrobial formulations may be used to control burn wound sepsis. An understanding of the barrier properties of eschar tissue is essential for optimal design of topical antimicrobial formulations. To date, little research has been conducted on the permeability of eschar. Silver sulphadiazine (SSD) is the most frequently used topical agent in burn management. In this study, the permeation of sulphadiazine from aqueous saturated solutions of SSD through human full-thickness burn eschar tissue was studied and compared with permeability through silicone and Carbosil as model membranes. The permeation of sulphadiazine through eschar tissue was significantly higher than that through silicone and Carbosil membranes (P < 0.05). Deconvolution of the data showed that the apparent sulphadiazine diffusion coefficient was much higher in eschar tissue and was comparable to transport through an aqueous protein gel. Further studies on a greater number of compounds are suggested to elucidate the utility of such membranes as predictive models of drug permeability through eschar tissue.

Increasing percent burn is correlated with increasing inflammation in an adult rodent model

Burn injury has been associated with systemic/compartmental inflammatory responses and myocardial dysfunction. We hypothesized that burn size correlates with the extent of cardiac inflammatory response/contractile dysfunction. Adult male Sprague-Dawley rats were divided to receive anesthesia, a 3-degree burn covering 20%, 30%, 40%, or 60% total body surface area (TBSA) plus fluid resuscitation (lactated Ringer, 4 mL/kg per percent burn); sham burn animals were included as controls. There were seven rats in each group. Rats were euthanized Twenty-four h postburn, and TNF-alpha, IL-1beta, and IL-6 were measured in the plasma and in supernatant from isolated cardiac myocytes by enzyme-linked immunosorbent assay. In addition, left ventricular function (Langendorff) was studied in vitro, and troponin levels were measured by enzyme-linked immunosorbent assay. There were progressive, statistically significant increases in plasma and myocyte inflammatory cytokine levels, as well as plasma troponin with increasing burn size. Similarly, left ventricular pressure (in millimeters of mercury) and +/-dP/dtmax (in millimeters of mercury per second) progressively fell with increasing burn size. However, myocardial contractile depression induced by 60% TBSA burn was similar to that produced by 40% TBSA burn. These data suggest that the degree of inflammatory response, cardiac tissue injury, and myocardial contractile depression were correlated directly with the percent TBSA burn. However, unlike inflammation and cardiac tissue damage, myocardial contractile depression reached a plateau, with maximal myocardial contraction and relaxation defects observed at 40% TBSA burn, which were not further aggravated by a larger (60%) burn.

CO liberated from CORM-2 modulates the inflammatory response in the liver of thermally injured mice

AIM

To explore the effects of CO-releasing molecules [tricarbonyldichlororuthenium (II) dimer, CORM-2]-liberated CO on attenuation of inflammatory responses in liver of an experimental animal model of thermal injury and to investigate the associated potential mechanisms.

METHODS

Thirty-six mice were assigned to three groups in three respective experiments. In each experiment, mice in sham group (n=4) received sham thermal injury, whereas mice in burn group (n=4) received a 15% of total body surface area (TBSA) full-thickness thermal injury, and mice in burn+CORM-2 group (n=4) received the same thermal injury with immediate administration of CORM-2 (8 mg/kg, iv). Hepatic tissue sections were stained with hematoxylin and eosin and examined under a light microscope. Levels of aminotransferases (ALT and AST) and nitric oxide (NO) were measured by biochemical methods. Tumor necrosis factor-alpha (TNF-alpha) and interleukin (IL-1beta) activity, and the protein expression of iNOS and HO-1 in serum and tissue homogenates were assessed. In in vitro experiments, Kupffer cells were stimulated with LPS (10 microg/mL) for 4 h in the presence or absence of CORM-2 (10-100 micromol/L). Subsequently, the expression levels of TNF-alpha and NO production were assessed.

RESULTS

Pro-inflammatory mediators (TNF-alpha, IL-1beta, NO) in serum and liver homogenates of thermally injured mice were significantly reduced by CORM-2 administration. This was accompanied by a decrease in the expression of iNOS while an increase in the expression of HO-1 in the liver tissue. In parallel, the concentrations of TNF-alpha and NO in supernatants of LPS-stimulated Kupffer cells co-incubated with CORM-2 (10-100 micromol/L) were also markedly decreased. Histological examination demonstrated that CORM-2 could attenuate the leukocytes infiltration to the liver tissue.

CONCLUSION

CORM-released CO modulates liver inflammation and significantly protects liver injury in burn mice by inhibiting the expression of iNOS and NO production, down-regulating the expression of pro-inflammatory mediators (TNF-alpha, IL-1beta).

Carbon liberated from CO-releasing molecules attenuates leukocyte infiltration in the small intestine of thermally injured mice

AIM

To determine whether Carbon (CO) liberated from CO-releasing molecules attenuates leukocyte infiltration in the small intestine of thermally injured mice.

METHODS

Thirty-six mice were assigned to four groups. Mice in the sham group (n = 9) were underwent to sham thermal injury; mice in the burn group (n = 9) received 15% total body surface area full-thickness thermal injury; mice in the burn + CORM-2 group (n = 9) were underwent to the same thermal injury with immediate administration of tricarbonyldichlororuthenium (II) dimer CORM-2 (8 mg/kg, i.v.); and mice in the burn+DMSO group (n = 9) were underwent to the same thermal injury with immediate administration of 160 muL bolus injection of 0.5% DMSO/saline. Histological alterations and granulocyte infiltration of the small intestine were assessed. Polymorphonuclear neutrophil (PMN) accumulation (myeloperoxidase assay) was assessed in mice mid-ileum. Activation of nuclear factor (NF)-kappa B, expression levels of intercellular adhesion molecule-1 (ICAM-1) and inducible heme oxygenase in mid-ileum were assessed.

RESULTS

Treatment of thermally injured mice with CORM-2 attenuated PMN accumulation and prevented activation of NF-kappa B in the small intestine. This was accompanied by a decrease in the expression of ICAM-1. In parallel, burn-induced granulocyte infiltration in mid-ileum was markedly decreased in the burn mice treated with CORM-2.

CONCLUSION

CORM-released CO attenuates leukocyte infiltration in the small intestine of thermally injured mice by interfering with NF-kappa B activation and protein expression of ICAM-1, and therefore suppressing the pro-adhesive phenotype of endothelial cells.

CO liberated from CORM-2 modulates the inflammatory response in the liver of thermally injured mice

AIM: To explore the effects of CO-releasing molecules [tricarbonyldichlororuthenium (II) dimer, CORM-2]-liberated CO on attenuation of inflammatory responses in liver of an experimental animal model of thermal injury and to investigate the associated potential mechanisms.

METHODS: Thirty-six mice were assigned to three groups in three respective experiments. In each experiment, mice in sham group (n = 4) received sham thermal injury, whereas mice in burn group (n = 4) received a 15% of total body surface area (TBSA) full-thickness thermal injury, and mice in burn + CORM-2 group (n = 4) received the same thermal injury with immediate administration of CORM-2 (8 mg/kg, iv). Hepatic tissue sections were stained with hematoxylin and eosin and examined under a light microscope. Levels of aminotransferases (ALT and AST) and nitric oxide (NO) were measured by biochemical methods. Tumor necrosis factor-α (TNF-α) and interleukin (IL-1β) activity, and the protein expression of iNOS and HO-1 in serum and tissue homogenates were assessed. In in vitro experiments, Kupffer cells were stimulated with LPS (10 &mgr;g/mL) for 4 h in the presence or absence of CORM-2 (10-100 &mgr;mol/L). Subsequently, the expression levels of TNF-α and NO production were assessed.

RESULTS: Pro-inflammatory mediators (TNF-α, IL-1β, NO) in serum and liver homogenates of thermally injured mice were significantly reduced by CORM-2 administration. This was accompanied by a decrease in the expression of iNOS while an increase in the expression of HO-1 in the liver tissue. In parallel, the concentrations of TNF-α and NO in supernatants of LPS-stimulated Kupffer cells co-incubated with CORM-2 (10-100 &mgr;mol/L) were also markedly decreased. Histological examination demonstrated that CORM-2 could attenuate the leukocytes infiltration to the liver tissue.

CONCLUSION: CORM-released CO modulates liver inflammation and significantly protects liver injury in burn mice by inhibiting the expression of iNOS and NO production, down-regulating the expression of pro-inflammatory mediators (TNF-α, IL-1β).

Carbon liberated from CO-releasing molecules attenuates leukocyte infiltration in the small intestine of thermally injured mice

AIM: To determine whether Carbon (CO) liberated from CO-releasing molecules attenuates leukocyte infiltration in the small intestine of thermally injured mice.

METHODS: Thirty-six mice were assigned to four groups. Mice in the sham group (n = 9) were underwent to sham thermal injury; mice in the burn group (n = 9) received 15% total body surface area full-thickness thermal injury; mice in the burn + CORM-2 group (n = 9) were underwent to the same thermal injury with immediate administration of tricarbonyldichlororuthenium (II) dimer CORM-2 (8 mg/kg, i.v.); and mice in the burn+DMSO group (n = 9) were underwent to the same thermal injury with immediate administration of 160 μL bolus injection of 0.5% DMSO/saline. Histological alterations and granulocyte infiltration of the small intestine were assessed. Polymorphonuclear neutrophil (PMN) accumulation (myeloperoxidase assay) was assessed in mice mid-ileum. Activation of nuclear factor (NF)-κΒ, expression levels of intercellular adhesion molecule-1 (ICAM-1) and inducible heme oxygenase in mid-ileum were assessed.

RESULTS: Treatment of thermally injured mice with CORM-2 attenuated PMN accumulation and prevented activation of NF-κΒ in the small intestine. This was accompanied by a decrease in the expression of ICAM-1. In parallel, burn-induced granulocyte infiltration in mid-ileum was markedly decreased in the burn mice treated with CORM-2.

CONCLUSION: CORM-released CO attenuates leukocyte infiltration in the small intestine of thermally injured mice by interfering with NF-κΒ activation and protein expression of ICAM-1, and therefore suppressing the pro-adhesive phenotype of endothelial cells.

Bactericidal/permeability increasing protein attenuates the myocardial inflammation/dysfunction that occurs with burn complicated by subsequent infection

Intubation and mechanical ventilation after burn contribute to pneumonia-related infection. Although postburn presence or absence of endotoxin has been described, inactivation of Toll-like receptor 4 signaling has been shown to improve postburn organ function, suggesting that LPS participates in burn-related susceptibility to infection. We hypothesized that bactericidal/permeability-increasing protein (rBPI) given postburn would attenuate myocardial inflammation/dysfunction associated with postburn septic challenge given 7 days postburn. Rats were given burn over 40% total body surface area, lactated Ringer 4 ml.kg(-1).% burn(-1); burns received either vehicle or rBPI, 1 mg.kg(-1).h(-1) for 48 h postburn. Postburn day 7, subgroups of burns and shams were given intratracheal Klebsiella pneumoniae, 4 x 10(6) CFU to produce burn complicated by sepsis; additional sham and burn subgroups received intratracheal vehicle to produce sham sepsis. Vehicle-treated groups: 1) sham burn + sham sepsis 2) sham burn + sepsis, 3) burn + sham sepsis, 4) burn + sepsis. rBPI-treated groups: 5) sham burn + sham sepsis, 6) sham burn + sepsis, 7) burn + sham sepsis, 8) burn + sepsis. Cardiomyocyte cytokine secretion and myocardial function were studied 24 h after septic challenge, postburn day 8. Pneumonia-related infection 8 days after vehicle-treated burn produced myocyte cytokine secretion (pg/ml), indicated by increased myocyte TNF-alpha, 549 +/- 46; IL-1beta, 50 +/- 8; IL-6, 286 +/- 3 levels compared with levels in sham myocytes (TNF-alpha, 88 +/- 11; IL-1beta, 7 +/- 1; IL-6, 74 +/- 10; P < 0.05). Contractile dysfunction was evident from lower left ventricular pressure +/-dP/dt values in this group compared with sham. rBPI attenuated myocyte cytokine responses to septic challenge and improved contractile function, suggesting that burn-related mobilization of microbial-like products contribute to postburn susceptibility to infection.

Cardiac mitochondrial damage and inflammation responses in sepsis

BACKGROUND AND PURPOSE

Studies in sepsis suggest that mitochondria mediate multiple organ dysfunction, including cardiac failure; however, the underlying molecular mechanisms remain elusive. This study examined changes in mitochondrial membrane integrity, antioxidant activities, and oxidative stress in the heart after infectious challenge (intratracheal Streptococcus pneumoniae, 4 x 10(6) colony-forming units). Inflammation responses also were examined.

METHODS

Cardiac tissues were harvested from Sprague-Dawley rats 4, 8, 12, and 24 h after bacterial challenge (or intratracheal vehicle for sham-treated animals) and homogenized, followed by preparation of subcellular fractions (mitochondrial, cytosol, and nuclei) or whole-tissue lysate. We examined mitochondrial outer membrane damage and cytochrome C translocation to evaluate mitochondrial integrity, mitochondrial lipid and protein oxidation to assess oxidative stress, and mitochondrial superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities to estimate antioxidant defense. In addition, we measured nuclear factor-kappa B (NF-kappaB) activation in myocardium and cytokine production to investigate inflammatory responses to septic challenge.

RESULTS

Oxidation of mitochondrial protein and lipid was evident 4 h through 24 h after bacterial challenge. Mitochondrial outer membrane damage and cytochrome C release were accompanied by down-regulation of mitochondrial SOD and GPx activity. After bacterial challenge, systemic and myocardial cytokine production increased progressively, and NF-kappaB was activated gradually.

CONCLUSION

Sepsis impaired cardiac mitochondria by damaging membrane integrity, increasing oxidative stress, and altering defenses against reactive oxygen species. These alterations occur earlier than or simultaneously with inflammatory responses in myocardium after infectious challenge, suggesting that mitochondria play a role in modulating inflammation in sepsis.

Reducing susceptibility to bacteremia after experimental burn injury: a role for selective decontamination of the digestive tract

We proposed that selective decontamination of the digestive tract (SDD) initiated after experimental burn injury would decrease myocardial inflammation and dysfunction after a second insult such as septic challenge. Rats were divided into eight experimental groups. Groups included sham burn plus sham sepsis, burn alone, sepsis alone, and burn plus sepsis given either water by oral gavage for 5 days after burn (or sham burn) or given oral antibiotics (polymyxin E, 15 mg; tobramycin, 6 mg; 5-flucytosin, 100 mg given by oral gavage, 2x daily for 5 days after burn or sham burn). Cardiac function and inflammation were studied 24 h after septic challenge. In the absence of SDD, burn alone, sepsis alone, or burn plus septic challenge promoted cardiac myocyte secretion of TNF-alpha (burn, 174+/-11; sepsis, 269+/-19; burn+sepsis, 453+/-14 pg/ml), IL-1beta (burn, 35+/-2; sepsis, 29+/-1; burn+sepsis, 48+/-7 pg/ml), and IL-6 (burn, 143+/-18; sepsis, 116+/-3; burn+sepsis, 248+/-12 pg/ml) compared with values measured in sham (TNF-alpha, 3+/-1; IL-1beta, 1+/-0.4; IL-6, 6+/-1.5 pg/ml) (P<0.05). Impaired ventricular contraction and relaxation responses were evident in the absence of SDD [burn+sepsis: left ventricular pressure (LVP), 65+/-4 mmHg; rate of LVP rise (+dP/dt), 1,320+/-131 mmHg/s compared with values measured in sham: LVP, 96+/-4 mmHg; +dP/dt, 2,095+/-99 mmHg/s, P<0.05]. SDD treatment of experimental burn attenuated septic challenge-related inflammatory responses and improved myocardial contractile responses, producing cardiac TNF-alpha, IL-1beta, and IL-6 levels, LVP, +dP/dt, and rate of LVP fall (-dP/dt) values that were significantly better (P<0.05) than values measured in burn plus sepsis in the absence of SDD. This work confirms that endogenous gut organisms contribute to sensitivity to subsequent infectious challenge.

Role of interleukin-6 in cardiac inflammation and dysfunction after burn complicated by sepsis

To examine the role of myocardial interleukin-6 (IL-6) in myocardial inflammation and dysfunction after burn complicated by sepsis, we performed 40% total body surface area contact burn followed by late (7 days) Streptococcus pneumoniae pneumonia sepsis in wild-type (WT) mice, IL-6 knockout (IL-6 KO) mice, and transgenic mice overexpressing IL-6 in the myocardium (TG). Twenty-four hours after sepsis was induced, isolated cardiomyocytes were harvested and cultured in vitro, and supernatant concentrations of IL-6 and tumor necrosis factor (TNF)-alpha were measured. Cardiomyocyte intracellular calcium ([Ca(2+)](i)) and sodium ([Na(+)](i)) concentrations were also determined. Separate mice in each group underwent in vivo global hemodynamic and cardiac function assessment by cannulation of the carotid artery and insertion of a left ventricular pressure volume conductance catheter. Hearts from these mice were collected for histopathological assessment of inflammatory response, fibrosis, and apoptosis. In the WT group, there was an increase in cardiomyocyte TNF-alpha, [Ca(2+)](i), and [Na(+)](i) after burn plus sepsis, along with cardiac contractile dysfunction, inflammation, and apoptosis. These changes were attenuated in the IL-6 KO group but accentuated in the TG group. We conclude myocardial IL-6 mediates cardiac inflammation and contractile dysfunction after burn plus sepsis.

Antioxidant vitamin therapy alters sepsis-related apoptotic myocardial activity and inflammatory responses

This study examined the effects of antioxidant vitamins on several aspects of sepsis-related myocardial signaling cascades. Sprague-Dawley rats were divided into four groups: group 1, vehicle-treated shams; group 2, sham-operated rats given antioxidant vitamins (vitamin C, 24 mg/kg; vitamin E, 20 U/kg; vitamin A, 417 U/kg; and zinc, 3.7 ng/kg) by oral gavage in 0.5 ml water twice daily for 3 days and no septic challenge (vitamin-treated, sham-operated rats); group 3, intratracheal delivery of Streptococcus pneumoniae, 4 × 106 colony forming units in a volume of 0.3 ml phosphate buffer solution; group 4, S. pneumonia challenge as described for group 3 plus antioxidant vitamins (as described for group 2). Hearts collected 24 h after septic challenge were used to examine several aspects of cell signaling and ventricular function. As a result, when compared with sham-operated rats, sepsis in the absence of antioxidant therapy promoted NF-κB activation, increased mitochondrial cytochrome c release, increased myocyte cytokine secretion, increased caspase activation, and impaired left ventricular function. Antioxidant vitamin therapy plus septic challenge prevented NF-κB activation, reduced mitochondrial cytochrome c release, decreased caspase activity, abrogated cardiomyocyte secretion of inflammatory cytokines, and improved myocardial contractile function. In conclusion, antioxidant vitamin therapy abrogated myocardial inflammatory cytokine signaling and attenuated sepsis-related contractile dysfunction, suggesting that antioxidant vitamin therapy may be a potential approach to treat injury and disease states characterized by myocardial dysfunction.

Effects of burn injury on myocardial signaling and cytokine secretion: Possible role of PKC

This study examined the effects of major burn injury on the cellular distribution of several PKC isoforms in adult rat hearts and examined the hypothesis that PKC plays a regulatory role in cardiomyocyte cytokine secretion. Burn trauma was given over 40% total body surface area in Sprague-Dawley rats. An in vitro model of burn injury included addition of burn serum, 10% by volume, to primary cardiomyocyte cultures (collagen perfusion). In vivo burn injury produced redistribution of PKCdelta, PKCepsilon, and PKCalpha from the cytosol (soluble) to the membrane (particulate) component of the myocardium. This activation of the PKC isoforms was evident 2 h after burn injury and progressively increased over 24 h postburn. Addition of burn serum to isolated myocytes produced similar PKC isoform redistribution from the soluble to the particulate compartment, promoted myocyte Ca2+ and Na+ loading, and promoted robust myocyte secretion of inflammatory cytokines similar to that reported after in vivo burn injury. Pretreating cardiomyocytes with either calphostin or PKCepsilon inhibitory peptide, a potent inhibitor of PKCepsilon, prevented burn serum-related redistribution of the PKCepsilon isoform and prevented burn serum-related cardiomyocyte secretion of TNF-alpha, IL-1beta, IL-6, and IL-10. These data suggest that the PKCepsilon isoform plays a pivotal role in myocardial inflammatory response to injury, altering cardiac function by modulating cardiomyocyte inflammatory cytokine response to injury.

Murine in vivo myocardial contractile dysfunction after burn injury is exacerbated by pneumonia sepsis

We evaluated hemodynamic and cardiac contractile dysfunction in a murine model of 40% contact burn complicated by Streptococcus pneumoniae (1 x 10(5) CFU) sepsis. Male, 9- to 10-week-old C57/BL6 mice were divided into the following groups: sham burn, sham sepsis; 24 h after burn alone; 24 h after sepsis alone; 7 days after burn alone; and 7 days after burn followed by pneumonia sepsis. Hemodynamic and cardiac contractile function was assessed with carotid artery cannulation and left ventricular pressure-volume analysis. At 24 h after burn, there were significant decreases in all load-insensitive contractility variables including the end-systolic pressure volume relationship, preload-recruitable stroke work, and maximum elastance, but there were no changes in global hemodynamics. Twenty-four hours after sepsis, there was similar cardiac contractile dysfunction, along with a decrease in cardiac output, but mean arterial pressure was maintained with an increase in systemic vascular resistance. Late burn (7 days) was associated with a recovery of all contractility variables except the end-systolic pressure volume relationship. However, sepsis induced during the late burn period was associated with a significant decrease in heart rate and cardiac output, but mean arterial pressure was still maintained with increased systemic vascular resistance. With burn complicated by sepsis, all cardiac contractility variables showed profound contractile dysfunction. Our data indicate that burn complicated by sepsis is associated with more pronounced cardiac contractile dysfunction than burn alone or sepsis alone.

Hypertonic saline dextran after burn injury decreases inflammatory cytokine responses to subsequent pneumonia-related sepsis

The present study examined the hypothesis that hypertonic saline dextran (HSD), given after an initial insult, attenuates exaggerated inflammation that occurs with a second insult. Adult rats (n = 15 per group) were divided into groups 1 (sham burn), 2 [40% total body surface area burn + 4 ml/kg isotonic saline (IS) + 4 ml.kg(-1).% burn(-1) lactated Ringer solution (LR)], and 3 (burn + 4 ml/kg HSD + LR), all studied 24 h after burns. Groups 4 (sham burn), 5 (burn + IS + LR), and 6 (burns + HSD + LR) received intratracheal (IT) vehicle 7 days after burns; groups 7 (burn + IS + LR) and 8 (burn + HSD + LR) received IT Streptococcus pneumoniae (4 x 10(6) colony-forming units) 7 days after burn. Groups 4-8 were studied 8 days after burn and 24 h after IT septic challenge. When compared with sham burn, contractile defects occurred 24 h after burn in IS-treated but not HSD-treated burns. Cardiac inflammatory responses (pg/ml TNF-alpha) were evident with IS (170 +/- 10) but not HSD (45 +/- 5) treatment vs. sham treatment (80 +/- 15). Pneumonia-related sepsis 8 days after IS-treated burns (group 7) exacerbated TNF-alpha responses/contractile dysfunction vs. IS-treated burns in the absence of sepsis (P < 0.05). Sepsis that occurred after HSD-treated burns (group 8) had less myocyte TNF-alpha secretion/better contractile function than IS-treated burns given septic challenge (group 7, P < 0.05). We conclude that an initial burn injury exacerbates myocardial inflammation/dysfunction occurring with a second insult; giving HSD after the initial insult attenuates myocardial inflammation/dysfunction associated with a second hit, suggesting that HSD reduces postinjury risk for infectious complications.

Sequential ELISA to profile multiple cytokines from small volumes

Due to the low cost and relative effectiveness the enzyme-linked immunosorbent assay (ELISA) is widely used to measure the concentration of inflammatory cytokines in plasma and other sources. Blood volume represents a limiting factor in those mouse models requiring repeated sample collection at multiple time intervals to monitor the trajectory of inflammatory processes. The small blood volumes in such scenarios restrict the array of cytokines that can be measured using the traditional ELISA. The implementation of the sequential ELISA protocol presented here can dramatically increase the number of measured cytokines, since the plasma samples are not discarded after the initial assay but re-used to measure additional selected inflammatory proteins in consecutive tests. From the original 20 mul of blood volume collected, up to fifteen cytokines can be successfully assayed in five consecutive cycles. With more unstable cytokines analyzed in the initial cycles, no inter-assay interference and/or deterioration of samples occurs. The sequential ELISA technique based on commercially-available antibody pairs can be an attractive alternative to more advanced, costly methods. Given the simplistic validation procedure, the proposed sequential ELISA protocol has a wide potential for further modifications to include other inflammation-related targets.

Role of cytosolic vs. mitochondrial Ca2+accumulation in burn injury-related myocardial inflammation and function

This study was designed to examine the role of mitochondrial Ca2+homeostasis in burn-related myocardial inflammation. We hypothesized that mitochondrial Ca2+is a primary modulator of cardiomyocyte TNF-α, IL-1β, and IL-6 responses to injury and infection. Ventricular myocytes were prepared by Langendorff perfusion of hearts from adult rats subjected to sham burn or burn injury over 40% of total body surface area to produce enzymatic (collagenase) digestion. Isolated cardiomyocytes were suspended in MEM, cell number was determined, and aliquots of myocytes from each experimental group were loaded with fura 2-AM (2 μg/ml) for 1) 45 min at room temperature to measure total cellular Ca2+, 2) 45 min at 30°C followed by incubation at 37°C for 2 h to eliminate cytosolic fluorescence, and 3) 20 min at 37°C in MnCl2(200 μM)-containing buffer to quench cytosolic fura 2-AM signal. In vitro studies included preparation of myocytes from control hearts and challenge of myocytes with LPS or burn serum (BS), which have been shown to increase cytosolic Ca2+. Additional aliquots of myocytes were challenged with LPS or BS with or without a selective inhibitor of mitochondrial Ca2+, ruthenium red (RR). All cells were examined on a stage-inverted microscope that was interfaced with the InCyt Im2 fluorescence imaging system. Heat treatment or MnCl2challenge eliminated myocyte cytosolic fluorescence, whereas cells maintained at room temperature retained 95% of their initial fluorescence. Compared with Ca2+levels measured in sham myocytes, burn trauma increased cytosolic Ca2+from 90 ± 3 to 293 ± 6 nM ( P < 0.05) and mitochondrial Ca2+from 24 ± 1 to 75 ± 2 nM ( P < 0.05). LPS (25 μg/5 × 104cells) or BS (10% by volume) challenge for 18 h increased cardiomyocyte cytosolic and mitochondrial Ca2+and promoted myocyte secretion of TNF-α, IL-1β, and IL-6. RR pretreatment decreased LPS- and BS-related rise in mitochondrial Ca2+and cytokine secretion but had no effect on cytosolic Ca2+. BS challenge in perfused control hearts impaired myocardial contraction/relaxation, and RR pretreatment of hearts prevented BS-related myocardial contractile dysfunction. Our data suggest that a rise in mitochondrial Ca2+is one modulator of myocardial inflammation and dysfunction in injury states such as sepsis and burn trauma.

Myocardial inflammatory responses to sepsis complicated by previous burn injury

BACKGROUND

It is generally accepted that an initial injury such as burn trauma alters immune function such that a second insult increases the morbidity and mortality over that observed with each individual insult. We have shown previously that either burn trauma or sepsis promotes cardiomyocyte secretion of TNF-alpha and IL-1beta, cytokines that have been shown to produce myocardial contractile dysfunction. This study determined whether a previous burn injury (given eight days prior to sepsis) (1) provides a preconditioning phenomenon, decreasing inflammatory responses to a second insult or (2) exacerbates inflammatory response observed with either injury alone.

METHODS

Anesthetized Sprague-Dawley rats were given either burn injury over 40% total body surface area, sepsis alone (intratracheal S. pneumoniae, 4 x 10(6) colony forming units) or sepsis eight days after burn; all rats received lactated Ringer's solution. Hearts harvested 24 h after onset of sepsis alone or sepsis plus eight-day burn were used to (1) isolate cardiomyocytes (collagenase) or (2) assess contractile function (Langendorff). Cardiomyocytes loaded with 2 microg/mL Fura-2AM or sodium-binding benzofuran isophthalate were used to measure intracellular calcium and sodium concentrations (Nikon inverted microscope, Grooney optics, InCyt Im2 Fluorescence Imaging System). Additional cardiomyocytes were used to measure myocyte-secreted TNFalpha, IL-1, IL-6, IL-10 (pg/ml, ELISA).

RESULTS

Either burn trauma alone or sepsis alone promoted TNF-alpha, IL-1beta, nitric oxide, IL6 and IL-10 secretion by cardiomyocytes (p < 0.05). Producing aspiration-related pneumonia eight days postburn produced myocardial pro- and anti-inflammatory responses and increased myocyte Ca2+/Na+ concentrations to a significantly greater degree than the responses observed after either insult alone.

CONCLUSIONS

A previous burn injury alters myocardial inflammatory responses, predisposing the burn-injured subject to exaggerated inflammation, which correlates with greater myocardial dysfunction.

Gender-related differences in myocardial inflammatory and contractile responses to major burn trauma

Gender-related differences in immune responses to hemorrhage and sepsis have been described. However, most trauma studies continue to limit experimental models to males to avoid the variable responses associated with hormonal fluctuation in proestrus/estrus females. In the present study, male and female (either diestrus or proestrus/estrus) Sprague-Dawley rats (250–325 g) were given a third-degree scald burn over 40% total body surface area and fluid resuscitated (4 ml/kg per %burn of lactated Ringer solution); sham burn males and diestrus as well as sham burn proestrus/estrus female rats were included to provide controls. Twenty-four hours postburn, hearts were either perfused to examine mechanical function (Langendorff, n = 8 to 9 hearts/group) or to prepare cardiomyocytes (collagenase digestion, n = 4 to 5 hearts/group). Left ventricular developed pressure and the positive and negative first derivative of left ventricular pressure responses to increases in preload were significantly lower in burned males compared with responses measured in either burned proestrus/estrus or burned diestrus females; burn trauma increased cardiomyocyte secretion of tumor necrosis factor-α, interleukin-1β, and nitric oxide to a lesser extent in proestrus/estrus females than levels secreted by either diestrus females or males. Similarly, myocytes from proestrus/estrus females accumulated significantly less sodium/calcium compared with values measured in males ( P < 0.05). Our data confirm gender-related differences in myocardial function and myocardial inflammatory responses to burn injury.