CARDIOMYOCYTE FUNCTION AFTER BURN INJURY AND LIPOPOLYSACCHARIDE EXPOSURE: SINGLE-CELL CONTRACTION ANALYSIS AND CYTOKINE SECRETION PROFILE

The effects of Gram-positive and Gram-negative bacterial toxins (LTA & LPS) on cardiac function in Drosophila melanogaster larvae

The effects of Gram negative and positive bacterial sepsis depend on the type of toxins released, such as lipopolysaccharides (LPS) or lipoteichoic acid (LTA). Previous studies show LPS to rapidly hyperpolarize larval Drosophila skeletal muscle, followed by desensitization and return to baseline. In larvae, heart rate increased then decreased with exposure to LPS. However, responses to LTA, as well as the combination of LTA and LPS, on the larval Drosophila heart have not been previously examined. This study examined the effects of LTA and a cocktail of LTA and LPS on heart rate. The combined effects were examined by first treating with either LTA or LPS only, and then with the cocktail. The results showed a rapid increase in heart rate upon LTA application, followed by a gradual decline over time. When applying LTA followed by the cocktail, an increase in the rate occurred. However, if LPS was applied before the cocktail, the rate continued declining. These responses indicate the receptors or cellular cascades responsible for controlling heart rate within seconds and the rapid desensitization are affected by LTA or LPS and a combination of the two. The mechanisms for rapid changes which are not regulated by gene expression by exposure to LTA or LPS or associated bacterial peptidoglycans have yet to be identified in cardiac tissues of any organism.

Dermal Nanoemulsion Treatment Reduces Burn Wound Conversion and Improves Skin Healing in a Porcine Model of Thermal Burn Injury

Burn wound progression is an inflammation-driven process where an initial partial-thickness thermal burn wound can evolve over time to a full-thickness injury. We have developed an oil-in-water nanoemulsion formulation (NB-201) containing benzalkonium chloride for use in burn wounds that is antimicrobial and potentially inhibits burn wound progression. We used a porcine burn injury model to evaluate the effect of topical nanoemulsion treatment on burn wound conversion and healing. Anesthetized swine received thermal burn wounds using a 25-cm2 surface area copper bar heated to 80°C. Three different concentrations of NB-201 (10, 20, or 40% nanoemulsion), silver sulfadiazine cream, or saline were applied to burned skin immediately after injury and on days 1, 2, 4, 7, 10, 14, and 18 postinjury. Digital images and skin biopsies were taken at each dressing change. Skin biopsy samples were stained for histological evaluation and graded. Skin tissue samples were also assayed for mediators of inflammation. Dermal treatment with NB-201 diminished thermal burn wound conversion to a full-thickness injury as determined by both histological and visual evaluation. Comparison of epithelial restoration on day 21 showed that 77.8% of the nanoemulsion-treated wounds had an epidermal injury score of 0 compared to 16.7% of the silver sulfadiazine-treated burns (P = .01). Silver sulfadiazine cream- and saline-treated wounds (controls) converted to full-thickness burns by day 4. Histological evaluation revealed reduced inflammation and evidence of skin injury in NB-201-treated sites compared to control wounds. The nanoemulsion-treated wounds often healed with complete regrowth of epithelium and no loss of hair follicles (NB-201: 4.8 ± 2.1, saline: 0 ± 0, silver sulfadiazine: 0 ± 0 hair follicles per 4-mm biopsy section, P < .05). Production of inflammatory mediators and sequestration of neutrophils were also inhibited by NB-201. Topically applied NB-201 prevented the progression of a partial-thickness burn wound to full-thickness injury and was associated with a concurrent decrease in dermal inflammation.

Whole body periodic acceleration (pGz) improves endotoxin induced cardiomyocyte contractile dysfunction and attenuates the inflammatory response in mice

Sepsis-induces myocardial contractile dysfunction. We previously showed that whole body periodic acceleration (pGz), the sinusoidal motion of the supine body head-foot ward direction significantly improves survival and decreases microvascular permeability in a lethal model of sepsis. We tested the hypothesis that pGz improves LPS induced cardiomyocyte contractile dysfunction and decreases LPS pro-inflammatory cytokine response when applied pre- or post-treatment. Isolated cardiomyocytes were obtained from mice that received LPS who had been pre-treated with pGz for three days (pGz-LPS) or control. Peak shortening (PS), maximal velocity of shortening (+dL/dt), and relengthening (-dL/dt) as well as diastolic intracellular calcium concentration ([Ca⁺²]_d), sodium ([Na⁺]_d), reactive oxygen species (ROS), and cardiac troponin (cTnT) production were measured. LPS decreased PS, +dL/dt, and -dL/dt, by 37%, 41% and 35% change respectively (p < 0.01), increased [Ca⁺²]_d, [Na⁺]_d, ROS, and cTnT by 343%, 122%, 298%, and 610% change respectively (p < 0.01) compared to control. pGz pre-treatment attenuated the parameters mentioned above. In a separate cohort, the effects of a lethal dose of LPS on protein expression of nitric oxide synthases (iNOS, eNOS, nNOS), pro- and anti-inflammatory cytokines in hearts of mice was studied in pre-treated with pGz for three days prior to LPS (pGz-LPS) and post-treated with pGz 30 min after LPS (LPS-pGz) were determined. LPS increased expression of early and late iNOS and decreased expression of eNOS, phosphorylated eNOS (p-eNOS), and nNOS. Both pre- and post-treatment with pGz markedly reduced early and late pro-inflammatory surge. Therefore, pre- and post-treatment with pGz improves LPS-induced cardiomyocyte dysfunction, decreases iNOS expression, and increases cytoprotective eNOS and nNOS, with decreased pro-inflammatory response. Such results have potential for translation to benefit outcomes in human sepsis.

Periodontal bacteria DNA findings in human cardiac tissue - Is there a link of periodontitis to heart valve disease?

BACKGROUND

The aim of the study was to detect periodontal pathogens DNA in atrial and myocardial tissue, and to investigate periodontal status and their connection to cardiac tissue inflammation.

METHODS

In 30 patients, biopsy samples were taken from the atrium (A) and the ventricle myocardium (M) during aortic valve surgery. The dental examination included the dental and periodontal status (PS) and a collection of a microbiological sample. The detection of 11 periodontal pathogens DNA in oral and heart samples was carried out using PCR. The heart samples were prepared for detecting the LPS-binding protein (LBP), and for inflammation scoring on immunohistochemistry (IHC), comprising macrophages (CD68), LPS-binding protein receptor (CD14), and LBP (big42).

RESULTS

28 (93%) patients showed moderate to severe periodontitis. The periodontal pathogens in the oral samples of all patients revealed a similar distribution (3-93%). To a lesser extent and with a different distribution, these bacteria DNA were also detected in atrium and myocardium (3-27%). The LBP was detected in higher amount in atrium (0.22±0.16) versus myocardium (0.13±0.13, p=0.001). IHC showed a higher inflammation score in atrial than myocardial tissue as well as for CD14, CD68 and for LBP. Additional, periodontal findings showed a significant correlation to CD14 and CD68.

CONCLUSION

The results provide evidence of the occurrence of oral bacteria DNA at the cardiac tissue, with a different impact on atrial and myocardial tissue inflammation. Influence of periodontal findings was identified, but their relevance is not yet distinct. Therefore further clinical investigations with long term implication are warranted.

TMEM43-S358L mutation enhances NF-κB-TGFβ signal cascade in arrhythmogenic right ventricular dysplasia/cardiomyopathy

Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is a genetic cardiac muscle disease that accounts for approximately 30% sudden cardiac death in young adults. The Ser358Leu mutation of transmembrane protein 43 (TMEM43) was commonly identified in the patients of highly lethal and fully penetrant ARVD subtype, ARVD5. Here, we generated TMEM43 S358L mouse to explore the underlying mechanism. This mouse strain showed the classic pathologies of ARVD patients, including structural abnormalities and cardiac fibrofatty. TMEM43 S358L mutation led to hyper-activated nuclear factor κB (NF-κB) activation in heart tissues and primary cardiomyocyte cells. Importantly, this hyper activation of NF-κB directly drove the expression of pro-fibrotic gene, transforming growth factor beta (TGFβ1), and enhanced downstream signal, indicating that TMEM43 S358L mutation up-regulates NF-κB-TGFβ signal cascade during ARVD cardiac fibrosis. Our study partially reveals the regulatory mechanism of ARVD development.

Fmr1 protects cardiomyocytes against lipopolysaccharide-induced myocardial injury

The present study explored the mechanisms by which fragile X mental retardation 1 (fmr1) overexpression inhibits lipopolysaccharide (LPS)-induced cardiomyocyte injury. Factors including oxidative stress reaction, mitochondrial membrane potential variation and cell apoptosis were evaluated. The viability of H9c2 cells was evaluated with a Cell Counting Kit-8 assay after cells were treated with LPS at different concentrations (0, 1, 3, 6 and 9 µg/ml) for various durations (4, 12 and 24 h). Flow cytometry was used to determine variations in reactive oxygen species (ROS), mitochondrial membrane potential and cell apoptosis. Reverse transcription-quantitative polymerase chain reaction and western blot analysis were performed to detect the levels of apoptosis-associated factors, and western blot analysis was used to determine the phosphorylation levels of phosphoinositide-3 kinase (PI3K), Akt and forkhead box (Fox)O3a. The results indicated that LPS decreased the viability of H9c2 cells in a dose- and time-dependent manner. Overexpression of fmr1 inhibited the LPS-induced decrease in the mitochondrial membrane potential and the production of ROS as well as apoptosis in H9c2 cells. Fmr1 also inhibited LPS-induced reductions in antioxidant enzyme activities, including those of superoxide dismutase and reduced/oxidized glutathione ratio, and decreased LPS-associated increases in the lipid peroxidation product malondialdehyde. Apoptosis-associated factors were identified to be involved in the effects of Fmr1. Overexpression of Fmr1 attenuated LPS-associated increases in the apoptosis-activating factors B-cell lymphoma 2 (Bcl-2)-associated X protein and caspase-3 and decreases in apoptosis inhibitors, including Bcl-2 and X-linked inhibitor of apoptosis protein. Fmr1 overexpression also reduced LPS-induced increases in the phosphorylation levels of PI3K, Akt and FoxO3a. In conclusion, fmr1 overexpression alleviated oxidative stress and apoptosis in H9c2 cardiomyocytes injured by LPS via regulating oxidative stress and apoptosis-associated factors, as well as the PI3K/Akt pathway. This information may provide a novel and effective therapeutic strategy for heart diseases.

CO2 permeability and carbonic anhydrase activity of rat cardiomyocytes

AIM

To determine the CO₂ permeability (P_CO2 ) of plasma membranes of cardiomyocytes. These cells were chosen because heart possesses the highest rate of O₂ consumption/CO₂ production in the body.

METHODS

Cardiomyocytes were isolated from rat hearts using the Langendorff technique. Cardiomyocyte suspensions exhibited a vitality of 2-14% and were studied by the previously described mass spectrometric ¹⁸ O-exchange technique deriving P_CO2 . We showed by mass spectrometry and by carbonic anhydrase (CA) staining that non-vital cardiomyocytes are free of CA and thus do not contribute to the mass spectrometric signal, which is determined exclusively by the fully functional vital cardiomyocytes.

RESULTS

Lysed cardiomyocytes yielded an intracellular CA activity for vital cells of 5070; that is, the rate of CO₂ hydration inside the cell is accelerated 5071-fold. Using this number, analyses of the mass spectrometric recordings from cardiomyocyte suspensions yield a P_CO2 of 0.10 cm s^-1 (SD ± 0.06, n = 15) at 37 °C.

CONCLUSION

In comparison with the P_CO2 of other cells, this value is quite high and about identical to that of the human red cell membrane. As no major protein CO₂ channels such as aquaporins 1 and 4 are present in rat cardiac sarcolemma, the high P_CO2 of this membrane is likely due to its low cholesterol content of about 0.2 (mol cholesterol)·(mol total membrane lipids)^-1 . Previous work predicted a P_CO2 of ≥0.1 cm s^-1 from this level of cholesterol. We conclude that the low cholesterol establishes a P_CO2 high enough to render the membrane resistance to CO₂ diffusion almost negligible, even under conditions of maximal O₂ consumption of the heart.

Characterizing the relationship between systemic inflammatory response syndrome and early cardiac dysfunction in traumatic brain injury

Systolic dysfunction was recently described following traumatic brain injury (TBI), and systemic inflammation may be a contributing mechanism. Our aims were to 1) examine the association between the early systemic inflammatory response syndrome (SIRS) and systolic cardiac dysfunction following TBI, and 2) describe the longitudinal change in SIRS criteria, cardiac function, and hemodynamic parameters during the first week of hospitalization. We used a secondary analysis of a prospective cohort study examining cardiac function (with transthoracic echocardiography on the first day and serially over the first week of hospitalization) in 32 moderate-severe isolated TBI patients, and quantified the admission and daily SIRS response to injury. We determined the association of admission SIRS and systolic dysfunction following TBI. Admission SIRS was present in 7 (21%) patients and was associated with systolic dysfunction on multivariable analysis (relative risk 4.01; 95% 1.16-13.79, p = .028). Both SIRS criteria and systolic cardiac function improved over the first week of hospitalization. In conclusion, early SIRS is common among patients with moderate-severe TBI, and the presence of SIRS criteria on admission is associated with systolic cardiac dysfunction following TBI.

Permissive role of AMPK and autophagy in adiponectin deficiency-accentuated myocardial injury and inflammation in endotoxemia

BACKGROUND

Adiponectin (APN), an adipose-derived adipokine, alleviates lipopolysaccharide (LPS)-induced injury in multiple organs including hearts although the underlying mechanism in endotoxemia remains elusive. This study was designed to examine the role of adiponectin in LPS-induced cardiac anomalies and inflammation as well as the underlying mechanism with a focus on autophagy - a conserved machinery for bulk degradation of intracellular components.

METHODS AND RESULTS

Wild-type (WT) and APN(-/-) mice were challenged with LPS (4mg/kg) or saline for 6h. Echocardiography, cardiomyocyte contractile and intracellular Ca(2+) properties were evaluated. Markers of autophagy, apoptosis and inflammation including LC3B, p62, Beclin1, AMPK, mTOR, ULK, Caspase 3, Bcl-2, Bax, TLR4, TRAF6, MyD88, IL-1B, TNFα, HMGB1, JNK and IκB were examined using Western blot or RT-PCR. Our results showed that LPS challenge reduced fractional shortening, compromised cardiomyocyte contractile capacity, intracellular Ca(2+) handling properties, apoptosis and inflammation, which were accentuated by adiponectin ablation. Adiponectin ablation unmasked the LPS-induced cardiac remodeling (left ventricular end systolic diameter) and prolongation of cell shortening. The detrimental effects of adiponectin ablation were associated with dampened autophagy in response to LPS through an AMPK-mTOR-ULK1-dependent mechanism. In vivo administration of AMPK activator AICAR or the autophagy inducer rapamycin effectively attenuated or obliterated LPS-induced and adiponectin deficiency-accentuated responses without affecting TLR4, TRAF6 and MyD88.

CONCLUSIONS

The findings suggest that AMPK and autophagy may play a permissive role in the adiponectin deficiency-exacerbated cardiac dysfunction, apoptosis and inflammation under LPS challenge possibly at the post-TLR4 receptor level.

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.

Cortistatin protects myocardium from endoplasmic reticulum stress induced apoptosis during sepsis

Sepsis and septic shock are common entities encountered in intensive care units. Myocardial depression is a well-recognized manifestation of organ dysfunction in sepsis, and myocardial apoptosis is a key step for this progression, which may contribute to cardiac contractile dysfunction. Increasing evidence suggested the anti-inflammatory role of cortistatin (CST) during lethal endotoxemia. However, the direct protective effect of CST on myocardial is still not clear. Here, we aimed to study whether CST can directly protect myocardial from apoptosis. To test that, we used cecal ligation and puncture (CLP) induced sepsis rat model. CST (175 µg/kg, intraperitoneal administration) was injected every 24 h before the model induction for 3 days. Electron microscopy, TUNEL staining, caspase-3 expression, and the Bcl-2/Bax ratio were used to measure myocardial apoptosis. In addition, the protein levels of endoplasmic reticulum stress (ERS) markers were overexpressed in sepsis. To further test whether CST can directly protect myocardial apoptosis from ERS, we compared dithiothreitol (DTT) induced cardiomyocyte (CM) ERS with or without CST in vitro. We found that CST strongly attenuated lipopolysaccharide (LPS) and DTT induced CM ERS. Blocking GHS-R1a, one of CST's receptors expressed by CMs, completely abrogated CST's protective effect. Finally, CST's protective effect was associated with the decrease of ERS both in vivo and in vitro. In conclusion, our results for the first time showed the previously unexpected role of CST to directly protect myocardial from apoptosis through inhibiting ERS and partly through GHS-R1a.

Third-degree hindpaw burn injury induced apoptosis of lumbar spinal cord ventral horn motor neurons and sciatic nerve and muscle atrophy in rats

Background. Severe burns result in hypercatabolic state and concomitant muscle atrophy that persists for several months, thereby limiting patient recovery. However, the effects of burns on the corresponding spinal dermatome remain unknown. This study aimed to investigate whether burns induce apoptosis of spinal cord ventral horn motor neurons (VHMNs) and consequently cause skeletal muscle wasting. Methods. Third-degree hindpaw burn injury with 1% total body surface area (TBSA) rats were euthanized 4 and 8 weeks after burn injury. The apoptosis profiles in the ventral horns of the lumbar spinal cords, sciatic nerves, and gastrocnemius muscles were examined. The Schwann cells in the sciatic nerve were marked with S100. The gastrocnemius muscles were harvested to measure the denervation atrophy. Result. The VHMNs apoptosis in the spinal cord was observed after inducing third-degree burns in the hindpaw. The S100 and TUNEL double-positive cells in the sciatic nerve increased significantly after the burn injury. Gastrocnemius muscle apoptosis and denervation atrophy area increased significantly after the burn injury. Conclusion. Local hindpaw burn induces apoptosis in VHMNs and Schwann cells in sciatic nerve, which causes corresponding gastrocnemius muscle denervation atrophy. Our results provided an animal model to evaluate burn-induced muscle wasting, and elucidate the underlying mechanisms.

Burn injury enhances bone formation in heterotopic ossification model

OBJECTIVE

To demonstrate the pro-osteogenic effect of burn injury on heterotopic bone formation using a novel burn ossicle in vivo model.

BACKGROUND

Heterotopic ossification (HO), or the abnormal formation of bone in soft tissue, is a troubling sequela of burn and trauma injuries. The exact mechanism by which burn injury influences bone formation is unknown. The aim of this study was to develop a mouse model to study the effect of burn injury on heterotopic bone formation. We hypothesized that burn injury would enhance early vascularization and subsequent bone formation of subcutaneously implanted mesenchymal stem cells.

METHODS

Mouse adipose-derived stem cells were harvested from C57/BL6 mice, transfected with a BMP-2 adenovirus, seeded on collagen scaffolds (ossicles), and implanted subcutaneously in the flank region of 8 adult mice. Burn and sham groups were created with exposure of 30% surface area on the dorsum to 60°C water or 30°C water for 18 seconds, respectively (n = 4/group). Heterotopic bone volume was analyzed in vivo by micro-computed tomography for 3 months. Histological analysis of vasculogenesis was performed with platelet endothelial cell adhesion molecule staining. Osteogenic histological analysis was performed by Safranin O, Picrosirius red, and aniline blue staining. Qualitative analysis of heterotopic bone composition was completed with ex vivo Raman spectroscopy.

RESULTS

Subcutaneously implanted ossicles formed heterotopic bone. Ossicles from mice with burn injuries developed significantly more bone than sham control mice, analyzed by micro-computed tomography at 1, 2, and 3 months (P < 0.05), and had enhanced early and late endochondral ossification as demonstrated by Safranin O, Picrosirius red, and aniline blue staining. In addition, burn injury enhanced vascularization of the ossicles (P < 0.05). All ossicles demonstrated chemical composition characteristic of bone as demonstrated by Raman spectroscopy.

CONCLUSIONS

Burn injury increases the predilection to osteogenic differentiation of ectopically implanted ossicles. Early differences in vascularity correlated with later bone development. Understanding the role of burn injury on heterotopic bone formation is an important first step toward the development of treatment strategies aimed to prevent unwanted and detrimental heterotopic bone formation.

Ablation of Akt2 protects against lipopolysaccharide-induced cardiac dysfunction: role of Akt ubiquitination E3 ligase TRAF6

Lipopolysaccharide (LPS), an essential component of the outer membrane of Gram-negative bacteria, plays a pivotal role in myocardial anomalies in sepsis. Recent evidence has depicted a role of Akt in LPS-induced cardiac sequelae although little information is available with regard to the contribution of Akt isoforms in the endotoxin-induced cardiac dysfunction. This study examined the effect of Akt2 knockout on LPS-induced myocardial contractile dysfunction and the underlying mechanism(s) with a focus on TNF receptor-associated factor 6 (TRAF6). Echocardiographic properties and cardiomyocyte contractile function [peak shortening (PS), maximal velocity of shortening/relengthening, time-to-PS, time-to-90% relengthening] were examined in wild-type and Akt2 knockout mice following LPS challenge (4mg/kg, 4h). LPS challenge enlarged LV end systolic diameter, reduced fractional shortening and cardiomyocyte contractile capacity, prolonged TR90, promoted apoptosis, upregulated caspase-3/-12, ubiquitin, and the ubiquitination E3 ligase TRAF6 as well as decreased mitochondrial membrane potential without affecting the levels of TNF-α, toll-like receptor 4 and the mitochondrial protein ALDH2. Although Akt2 knockout failed to affect myocardial function, apoptosis, and ubiquitination, it significantly attenuated or mitigated LPS-induced changes in cardiac contractile and mitochondrial function, apoptosis and ubiquitination but not TRAF6. LPS facilitated ubiquitination, phosphorylation of Akt, GSK3β and p38, the effect of which with the exception of p38 was ablated by Akt2 knockout. TRAF6 inhibitory peptide or RNA silencing significantly attenuated LPS-induced Akt2 ubiquitination, cardiac contractile anomalies and apoptosis. These data collectively suggested that TRAF6 may play a pivotal role in mediating LPS-induced cardiac injury via Akt2 ubiquitination.

Lipoteichoic acid from Staphylococcus aureus directly affects cardiomyocyte contractility and calcium transients

Lipoteichoic acid (LTA) is the key pathogenic factor of gram-positive bacteria and contributes significantly to organ dysfunction in sepsis, a frequent complication in critical care patients. We hypothesized that LTA directly affects cardiomyocyte function, thus contributing to cardiac failure in sepsis. This study was designed to evaluate the effects of LTA on contractile properties and calcium-transients of isolated adult rat cardiomyocytes. When myocytes were exposed to LTA for 1h prior to analysis, the amplitudes of calcium-transients as well as sarcomere shortening increased to 130% and 142% at 1 Hz stimulation frequency. Relengthening of sarcomeres as well as decay of calcium-transients was accelerated after LTA incubation. Exposure to LTA for 24 h resulted in significant depression of calcium-transients as well as of sarcomere shortening compared to controls. One of the major findings of our experiments is that LTA most likely affects calcium-handling of the cardiomyocytes. The effect is exacerbated by reduced extracellular calcium, which resembles the clinical situation in septic patients. Functionally, an early stimulating effect of LTA with increased contractility of the cardiomyocytes may be an in vitro reflection of early hyperdynamic phases in clinical sepsis. Septic disorders have been shown to induce late hypodynamic states of the contractile myocardium, which is also supported at the single-cell level in vitro by results of our 24h-exposure to LTA.

Early detection of burn induced heterotopic ossification using transcutaneous Raman spectroscopy

INTRODUCTION

Heterotopic ossification (HO), or the abnormal formation of bone in soft tissue, occurs in over 60% of major burn injuries and blast traumas. A significant need exists to improve the current diagnostic modalities for HO which are inadequate to diagnose and intervene on HO at early time-points. Raman spectroscopy has been used in previous studies to report on changes in bone composition during bone development but has not yet been applied to burn induced HO. In this study, we validate transcutaneous, in-vivo Raman spectroscopy as a methodology for early diagnosis of HO in mice following a burn injury.

METHODS

An Achilles tenotomy model was used to study HO formation. Following tenotomy, mice were divided into burn and sham groups with exposure of 30% surface area on the dorsum to 60° water or 30° water for 18s respectively. In-vivo, transcutaneous Raman spectroscopy was performed at early time points (5 days, 2 and 3 weeks) and a late time point (3 months) on both the tenotomized and non-injured leg. These same samples were then dissected down to the bone and ex-vivo Raman measurements were performed on the excised tissue. Bone formation was verified with Micro CT and histology at corresponding time-points.

RESULTS

Our Raman probe allowed non-invasive, transcutaneous evaluation of heterotopic bone formation. Raman data showed significantly increased bone mineral signaling in the tenotomy compared to control leg at 5 days post injury, with the difference increasing over time whereas Micro CT did not demonstrate heterotopic bone until three weeks. Ex-vivo Raman measurements showed significant differences in the amount of HO in the burn compared to sham groups and also showed differences in the spectra of new, ectopic bone compared to pre-existing cortical bone.

CONCLUSIONS

Burn injury increases the likelihood of developing HO when combined with traumatic injury. In our in-vivo mouse model, Raman spectroscopy allowed for detection of HO formation as early as 5 days post injury. Changes in bone mineral and matrix composition of the new bone were also evidenced in the Raman spectra which could facilitate early identification of HO and allow more timely therapy decisions for HO patients.

Chronic Akt activation attenuated lipopolysaccharide-induced cardiac dysfunction via Akt/GSK3β-dependent inhibition of apoptosis and ER stress

Sepsis is characterized by systematic inflammation and contributes to cardiac dysfunction. This study was designed to examine the effect of protein kinase B (Akt) activation on lipopolysaccharide-induced cardiac anomalies and underlying mechanism(s) involved. Mechanical and intracellular Ca²⁺ properties were examined in myocardium from wild-type and transgenic mice with cardiac-specific chronic Akt overexpression following LPS (4 mg/kg, i.p.) challenge. Akt signaling cascade (Akt, phosphatase and tensin homologue deleted on chromosome ten, glycogen synthase kinase 3 beta), stress signal (extracellular-signal-regulated kinases, c-Jun N-terminal kinases, p38), apoptotic markers (Bcl-2 associated X protein, caspase-3/-9), endoplasmic reticulum (ER) stress markers (glucose-regulated protein 78, growth arrest and DNA damage induced gene-153, eukaryotic initiation factor 2α), inflammatory markers (tumor necrosis factor α, interleukin-1β, interleukin-6) and autophagic markers (Beclin-1, light chain 3B, autophagy-related gene 7 and sequestosome 1) were evaluated. Our results revealed that LPS induced marked decrease in ejection fraction, fractional shortening, cardiomyocyte contractile capacity with dampened intracellular Ca²⁺ release and clearance, elevated reactive oxygen species (ROS) generation and decreased glutathione and glutathione disulfide (GSH/GSSG) ratio, increased ERK, JNK, p38, GRP78, Gadd153, eIF2α, BAX, caspase-3 and -9, downregulated B cell lymphoma 2 (Bcl-2), the effects of which were significantly attenuated or obliterated by Akt activation. Akt activation itself did not affect cardiac contractile and intracellular Ca²⁺ properties, ROS production, oxidative stress, apoptosis and ER stress. In addition, LPS upregulated levels of Beclin-1, LC3B and Atg7, while suppressing p62 accumulation. Akt activation did not affect Beclin-1, LC3B, Atg7 and p62 in the presence or absence of LPS. Akt overexpression promoted phosphorylation of Akt and GSK3β. In vitro study using the GSK3β inhibitor SB216763 mimicked the response elicited by chronic Akt activation. Taken together, these data showed that Akt activation ameliorated LPS-induced cardiac contractile and intracellular Ca²⁺ anomalies through inhibition of apoptosis and ER stress, possibly involving an Akt/GSK3β-dependent mechanism.

RETRACTED: Cardiac-specific overexpression of catalase attenuates lipopolysaccharide-induced myocardial contractile dysfunction: Role of autophagy

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. After an institutional investigation into the work of Dr. Jun Ren, University of Wyoming subsequently conducted an examination of other selected publications of Dr. Ren's under the direction of the HHS Office of Research Integrity. Based on the findings of this examination, the University of Wyoming recommended this article be retracted due to concerns regarding data irregularities inconsistent with published conclusions. Specifically, University of Wyoming found evidence of data irregularities and image reuse in Figure 2 that significantly affect the results and conclusions reported in the manuscript.

Burn-induced heart failure: lipopolysaccharide binding protein improves burn and endotoxin-induced cardiac contractility deficits

BACKGROUND

Burn injury is frequently complicated by bacterial infection. Following burn injury, exposure to endotoxin produces a measurable decrease in cardiomyocyte sarcomere contractile function. Lipopolysaccharide-binding protein (LBP) is an acute phase protein that potentiates the recognition of lipopolysaccharide (LPS) by binding to the lipid A moiety of LPS. In this study, we sought to determine the effect of recombinant rat LBP (rLBP) on cardiomyocyte sarcomere function after burn or sham injury in the presence or absence of bacterial endotoxin.

METHODS

Rats underwent a full-thickness 30% total body surface area scald or sham burn. At 24 h post-injury, cardiomyocytes were isolated, plated at 50,000 cells/well, and incubated with 50 μg/mL LPS and rLBP or chloramphenicol acetyltransferase (BVCat, an irrelevant control protein produced using the same expression system as rLBP) at concentrations by volume of 1%, 5%, 10%, and 30%. Subsets of cardiomyocytes were incubated with 5% rat serum or 30% rLBP and blocking experiments were conducted using an LBP-like synthetic peptide (LBPK95A). In vitro sarcomere function was measured using a variable rate video camera system with length detection software.

RESULTS

Co-culture of burn and sham injury derived cardiomyocytes with high-dose rLBP in the presence of LPS resulted in a significant reduction to the functional impairment observed in peak sarcomere shortening following exposure to LPS alone. LBP-like peptide LBPK95A at a concentration of 20 μg/mL, in the presence of LPS, abolished the ability of 30% rLBP and 5% rat serum to restore peak sarcomere shortening of cardiomyocytes isolated following burn injury to levels of function exhibited in the absence of endotoxin exposure.

CONCLUSIONS

In the setting of LPS challenge following burn injury, rLBP at high concentrations restores cardiomyocyte sarcomere contractile function in vitro. Rather than potentiating the recognition of LPS by the cellular LPS receptor complex, rLBP at high concentrations likely results in an inhibitory binding effect that minimizes the impact of endotoxin exposure on cardiomyocyte function following thermal injury.

Cardiac overexpression of metallothionein rescues cardiac contractile dysfunction and endoplasmic reticulum stress but not autophagy in sepsis

Sepsis is characterized by systematic inflammation where oxidative damage plays a key role in organ failure. This study was designed to examine the impact of the antioxidant metallothionein (MT) on lipopolysaccharide (LPS)-induced cardiac contractile and intracellular Ca(2+) dysfunction, oxidative stress, endoplasmic reticulum (ER) stress and autophagy. Mechanical and intracellular Ca(2+) properties were examined in hearts from FVB and cardiac-specific MT overexpression mice treated with LPS. Oxidative stress, activation of mitogen-activated protein kinase pathways (ERK, JNK and p38), ER stress, autophagy and inflammatory markers iNOS and TNFalpha were evaluated. Our data revealed enlarged end systolic diameter, decreased fractional shortening, myocyte peak shortening and maximal velocity of shortening/relengthening as well as prolonged duration of relengthening in LPS-treated FVB mice associated with reduced intracellular Ca(2+) release and decay. LPS treatment promoted oxidative stress (reduced glutathione/glutathione disulfide ratio and ROS generation). Western blot analysis revealed greater iNOS and TNFalpha, activation of ERK, JNK and p38, upregulation of ER stress markers GRP78, Gadd153, PERK and IRE1alpha, as well as the autophagy markers Beclin-1, LCB3 and Atg7 in LPS-treated mouse hearts without any change in total ERK, JNK and p38. Interestingly, these LPS-induced changes in echocardiographic, cardiomyocyte mechanical and intracellular Ca(2+) properties, ROS, stress signaling and ER stress (but not autophagy, iNOS and TNFalpha) were ablated by MT. Antioxidant N-acetylcysteine and the ER stress inhibitor tauroursodeoxycholic acid reversed LPS-elicited depression in cardiomyocyte contractile function. LPS activated AMPK and its downstream signaling ACC in conjunction with an elevated AMP/ATP ratio, which was unaffected by MT. Taken together, our data favor a beneficial effect of MT in the management of cardiac dysfunction in sepsis.

Local wound p38 MAPK inhibition attenuates burn-induced cardiac dysfunction

BACKGROUND

Topical inhibition of activated p38 MAPK within burn wounds attenuates the local and systemic inflammatory response. In this study, we investigated the effects of local activated p38 MAPK inhibition on burn-induced cardiac dysfunction.

METHODS

Using a standardized rat model of scald burn injury, rats were given a 30% total body surface area partial thickness burn or sham injury, and the wounds were treated with an activated p38 MAPK inhibitor (SB) or vehicle. Systemic blood pressure measurements were recorded in vivo followed by in vitro assessment of sarcomere contraction in single-cell suspensions of isolated cardiomyocytes.

RESULTS

Systolic blood pressure or maximum left ventricular pressures in vivo and peak cardiomyocyte sarcomere contractility in vitro were significantly reduced after burn injury. These functional deficits were abolished 24 h after burn injury following local p38 MAPK inhibition. In vitro incubation of normal cardiomyocytes with homogenate from burned skin or burn serum resulted in a similar pattern of impaired cardiomyocyte contractility. These effects were reversed in normal cardiomyocytes exposed to burn skin homogenates treated topically with a p38 MAPK inhibitor. A Western blot analysis showed that cardiac p38 MAPK activation was not affected by dermal blockade of activated p38 MAPK, arguing against systemic absorption of the inhibitor and indicating the involvement of systemic cytokine signaling.

CONCLUSION

Topical activated p38 MAPK inhibition within burned skin attenuates the release of proinflammatory mediators and prevents burn-induced cardiac dysfunction after thermal injury. These results support the inhibition of burn-wound inflammatory signaling as a new therapeutic approach to prevent potential postthermal injury multiorgan dysfunction syndrome.

Cardiac-specific overexpression of insulin-like growth factor I (IGF-1) rescues lipopolysaccharide-induced cardiac dysfunction and activation of stress signaling in murine cardiomyocytes

Lipopolysaccharide (LPS), a component of the outer membrane of Gram-negative bacteria, plays a key role in cardiac dysfunction in sepsis. Low circulating levels of insulin-like growth factor 1 (IGF-1) are found in sepsis, although the influence of IGF-1 on septic cardiac defect is unknown. This study was designed to examine the impact of IGF-1 on LPS-induced cardiac contractile and intracellular Ca2+ dysfunction, activation of stress signal and endoplasmic reticulum (ER) stress. Mechanical and intracellular Ca2+ properties were examined in cardiomyocytes from Fast Violet B and cardiac-specific IGF-1 overexpression mice treated with or without LPS (4 mg kg(-1), 6 h). Reactive oxygen species (ROS), protein carbonyl formation and apoptosis were measured. Activation of mitogen-activated protein kinase pathways (p38, c-jun N-terminal kinase [JNK] and extracellular signal-related kinase [ERK]), ER stress and apoptotic markers were evaluated using Western blot analysis. Our results revealed decreased peak shortening and maximal velocity of shortening/relengthening and prolonged duration of relengthening in LPS-treated Fast Violet B cardiomyocytes associated with reduced intracellular Ca2+ decay. Accumulation of ROS protein carbonyl and apoptosis were elevated after LPS treatment. Western blot analysis revealed activated p38 and JNK, up-regulated Bax, and the ER stress markers GRP78 and Gadd153 in LPS-treated mouse hearts without any change in ERK and Bcl-2. Total protein expression of p38, JNK, and ERK was unaffected by either LPS or IGF-1. Interestingly, these LPS-induced changes in mechanical and intracellular Ca2+ properties, ROS, protein carbonyl, apoptosis, stress signal activation, and ER stress markers were effectively ablated by IGF-1. In vitro LPS exposure (1 microg mL(-1)) produced cardiomyocyte mechanical dysfunction reminiscent of the in vivo setting, which was alleviated by exogenous IGF-1 (50 nM). These data collectively suggested a beneficial of IGF-1 in the management of cardiac dysfunction under sepsis.

Proestrus female rats are more resistant to right ventricular pressure overload

Multiple studies of left ventricular dysfunction suggest that females may be more resistant to ischemia or endotoxemia. However, sex differences in right ventricular (RV) responses to pressure overload and/or endotoxemia have not been elucidated. We hypothesized that females would maintain better RV function during acute pressure overload (APO), endotoxemia, or a simultaneous insult from both processes. Age-matched male and proestrus female Sprague-Dawley rats were given an intraperitoneal injection of either phosphate buffered saline or LPS. Six hours after injection, hearts were removed by median sternotomy and isolated via Langendorff. End-diastolic pressures were sequentially elevated past physiologic levels by increasing the volume of a latex balloon that was inserted into the RV. Male RV function was depressed to a greater degree after APO injury compared with that in females (developed pressure: male, 44.97 mmHg vs. female, 58.23 mmHg). Interestingly though, at a physiologic end-diastolic pressure of 5 mmHg, endotoxic males and females maintained equivalent RV function. However, with concurrent endotoxic insult and APO, RV function was better maintained in males as compared with that in females (developed pressure: male, 59% of control versus female, 41% of control). Furthermore, tissue levels of IL-1 and IL-6, but not IL-10, were increased after endotoxin exposure but did not differ based on sex. Through this study, we have shown that sex differences exist in RV dysfunction, and that different cardiac insults diversely affect myocardial function. Understanding these differences may allow for the implementation of novel therapeutic treatment options that are designed to attenuate RV cardiovascular collapse.

Cardiovascular distribution of the calcium sensing receptor before and after burns

Due to up-regulation of the parathyroid gland calcium-sensing receptor (CaR), burned children have hypocalcemic hypoparathyroidism, and decreased myocardial contractility. Our aim was to localize the CaR in the heart and measure receptor density changes due to burns. Heart and aorta samples from sheep subjected to 40% burn or sham conditions were probed for CaR via fluorescence microscopy. CaR was localized to endocardial endothelium, myocardial microvasculature, and fibroblasts and vessels of the aortic adventitia. CaR was not found in cardiomyocytes or smooth muscle cells. No differences in density of CaR or beta-adrenergic receptors were noted. No differences in CaR distribution were seen in the myocardium or aorta, in contrast to the parathyroid where burn injury up-regulates CaR. We suggest that CaR has a local, tissue-specific role, and functions in vascular calcium sensing for intravascular calcium deposition or regulation of other calcium channels after trauma or burn.

Role of p38 mitogen-activated protein kinase pathway on heart failure in the infant rat after burn injury

We examined the hypothesis that post-burn activation of the p38 mitogen-activated protein kinase (MAPK) pathway is one aspect of the signalling cascade culminating in post-burn secretion of tumour necrosis factor (TNF)-alpha which contributes to post-burn myocardial apoptosis. Studies were designed to determine the time course of the induction of p38MAPK, TNF-alpha and myocardial apoptosis after burn injury. Our quantitative bacterial culture data demonstrated that viable bacteria reached the heart, and Western blotting data identified the increase in the phosphorylation of p38MAPK at an early time after burn. The peak incidence of myocardial apoptosis was also seen at an early time after burn. The expression of TNF-alpha mRNA, infiltrated neutrophils and serum creatine phosphokinase myocardial band data peaked at a late time after burn. FR167653, a specific inhibitor of p38MAPK, prevented the induction of myocardial apoptosis, TNF-alpha expression and myocardial injury after burn. Presumably, the bacterial LPS-induced activation of p38MAPK pathway occurring at an early time after burn induced the subsequent myocardial apoptosis. The p38MAPK-induced activation of pro-inflammatory cytokine appeared to promote the degenerative myocardial injury at a late time after burn. Our present data provided evidence for the hypothesis that the p38MAPK pathway controls both myocardial apoptosis and the pro-inflammatory mediator.

C5a-blockade improves burn-induced cardiac dysfunction

We previously reported that generation of the anaphylatoxin C5a is linked to the development of cardiac dysfunction in sepsis due to C5a interaction with its receptor (C5aR) on cardiomyocytes. Burn injury involves inflammatory mechanisms that can lead to C5a generation as well. In this study, we investigated the effects of C5a blockade on burn-induced cardiac dysfunction. Using a standardized rat model of full thickness scald injury, left ventricular pressures were recorded in vivo followed by in vitro assessment of sarcomere contraction of single cardiomyocytes. Left ventricular pressures in vivo and cardiomyocyte sarcomere contractility in vitro were significantly reduced following burn injury. In the presence of anti-C5a Ab, these defects were greatly attenuated 1, 6, and 12 h after burn injury and completely abolished 24 h after burn. In vitro incubation of cardiomyocytes with bacterial LPS accentuated the impaired contractility, which was partially prevented in cardiomyocytes from burned rats that had received an anti-C5a Ab. Based on Western blot analyses, real-time PCR, and immunostaining of left ventricular heart tissue, there was a significant increase in cardiomyocyte expression of C5aR after burn injury. In conclusion, an in vivo blockade of C5a attenuates burn-induced cardiac dysfunction. Further deterioration of contractility due to the exposure of cardiomyocytes to LPS was partially prevented by C5a-blockade. These results suggest a linkage between C5a and burn-induced cardiac dysfunction and a possible contribution of LPS to these events.

The human embryonic stem cell-derived cardiomyocyte as a pharmacological model

Embryonic stem (ES) cells are specialised cells derived from the early embryo, which are capable of both sustained propagation in the undifferentiated state as well as subsequent differentiation into the majority of cell lineages. Human ES cells are being developed for clinical tissue repair, but a number of problems must be addressed before this becomes a reality. However, they also have potential for translational benefit through its use as a test system for screening pharmaceutical compounds. In the cardiac field, present model systems are not ideal for either screening or basic pharmacological/physiological studies. Cardiomyocytes produced from human ES differentiation have advantages for these purposes over the primary isolated cells or the small number of cell lines available. This review describes the methodology for obtaining cardiomyocytes from human embryonic stem cell-derived cardiomyocyte (hESCM), for increasing the proportion of cardiomyocytes in the preparation and for isolating single embryonic stem cell-derived cardiomyocyte (ESCM) from clusters. Their morphological, contractile and electrophysiological characteristics are compared to mature and immature primary cardiomyocytes. The advantages and disadvantages of the hESCM preparation for long term culture and genetic manipulation are described. Basic pharmacological studies on adrenoceptors and muscarinic receptors in hESCM have been performed, and have given stable and reproducible responses. Prolongation of repolarisation can be detected using hESCM cultured on multielectrode arrays (MEA). Human ESCM have a clear potential to improve model systems available for both basic scientific studies and pharmaceutical screening of cardiac target compounds.

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.

Complement-related molecular events in sepsis leading to heart failure

Despite intensive ongoing research efforts, the mortality of patients with sepsis remains unacceptably high. A significant number of clinical trials have failed to produce sufficient therapeutic strategies despite showing promising results in animal models. So far, many studies have focused on deterioration of the humoral and cellular components of the immune system, the main cause of death in septic patients being multi-organ failure. However, not much is known about the effects of the complement system on parenchymal cells of organs such as the heart. Recently, septic cardiomyopathy has been recognized as one of the major complications during sepsis, often determining the clinical outcome. In this review, we describe molecular events which are thought to be related to cardiac dysfunction during sepsis. A special emphasis will be placed on the complement system, which generates powerful anaphylatoxins (such as C5a) and which has recently been associated with septic cardiomyopathy. Together with the impact on cardiac function of various cytokines we will provide a synopsis of the current knowledge regarding the pathophysiology underlying cardiac failure during sepsis with a special emphasis on C5a and C5aR.

Recruitment of functionally active heart beta2-adrenoceptors in the initial phase of endotoxic shock in pithed rats

A supersensitivity of the beta-adrenoceptor-mediated chronotropic response has been demonstrated in atria isolated from rats subjected to septic shock. Our study was undertaken to investigate whether bacterial endotoxin/LPS affects the increase in heart rate induced by beta-adrenoceptor agonists in the rat also in vivo. In pithed and vagotomized rats, the nonselective beta-adrenoceptor agonist isoprenaline (0.05-0.15 nmol/kg) and agonists at the high- and low-affinity state of beta1-adrenoceptors, that is, prenalterol (0.3-3 nmol/kg) and (+/-)-4-[3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,3-dihydro-2H-benzimidazole-2-one (CGP 12177; 3-6 nmol/kg), respectively, and at beta2-adrenoceptors, that is, fenoterol (1-5 nmol/kg), increased heart rate by 50 to 60 beats/min. Administration of LPS (0.4, 1, and 1.5 mg/kg), under continuous infusion of vasopressin, dose-dependently amplified the chronotropic response to isoprenaline, prenalterol, and fenoterol (by 80%, 50%, and 100%, respectively) but not to CGP 12177. The beta2-adrenoceptor antagonist erythro-(+/-)-1-(7-methylindan-4-yloxy)-3-isopropylaminobutan-2-ol (ICI 118551 0.1 mumol/kg) did not affect the chronotropic responses of isoprenaline, fenoterol, and prenalterol under non-endotoxic conditions, but abolished the potentiation of tachycardia produced by LPS (1.5 mg/kg). The beta1-adrenoceptor antagonist (+/-)-2-hydroxy-5-[2-[[2-hydroxy-3-[4-[1-methyl-4-(trifluoromethyl)-1H-imidazol-2-yl]-phenoxy]propyl]-amino]ethoxy]-benzamide CGP 20712A; 0.1 mumol/kg almost completely reduced the chronotropic effects of isoprenaline, fenoterol, and prenalterol both in control rats and in animals exposed to LPS (1.5 mg/kg). We conclude that LPS sensitizes cardiac beta-adrenoceptors by recruiting functionally active beta2-adrenoceptors, but the amplification of tachycardia occurs only when both beta1- and beta2-adrenoceptors are concomitantly activated. The pithed rat may serve as a model to examine the beta-adrenoceptor supersensitivity in vivo.