Ventricular Myocyte Caspases Are Directly Responsible for Endotoxin-Induced Cardiac Dysfunction

MECHANISMS OF CARDIAC DYSFUNCTION IN SEPSIS

ABSTRACT

Studies in animal models of sepsis have elucidated an intricate network of signaling pathways that lead to the dysregulation of myocardial Ca 2+ handling and subsequently to a decrease in cardiac contractile force, in a sex- and model-dependent manner. After challenge with a lethal dose of LPS, male animals show a decrease in cellular Ca 2+ transients (ΔCa i ), with intact myofilament function, whereas female animals show myofilament dysfunction, with intact ΔCa i . Male mice challenged with a low, nonlethal dose of LPS also develop myofilament desensitization, with intact ΔCa i . In the cecal ligation and puncture (CLP) model, the causative mechanisms seem similar to those in the LPS model in male mice and are unknown in female subjects. ΔCa i decrease in male mice is primarily due to redox-dependent inhibition of sarco/endoplasmic reticulum Ca 2+ ATP-ase (SERCA). Reactive oxygen species (ROS) are overproduced by dysregulated mitochondria and the enzymes NADPH/NADH oxidase, cyclooxygenase, and xanthine oxidase. In addition to inhibiting SERCA, ROS amplify cardiomyocyte cytokine production and mitochondrial dysfunction, making the process self-propagating. In contrast, female animals may exhibit a natural redox resilience. Myofilament dysfunction is due to hyperphosphorylation of troponin I, troponin T cleavage by caspase-3, and overproduction of cGMP by NO-activated soluble guanylate cyclase. Depleted, dysfunctional, or uncoupled mitochondria likely synthesize less ATP in both sexes, but the role of energy deficit is not clear. NO produced by NO synthase (NOS)-3 and mitochondrial NOSs, protein kinases and phosphatases, the processes of autophagy and sarco/endoplasmic reticulum stress, and β-adrenergic insensitivity may also play currently uncertain roles.

Parecoxib attenuates inflammation injury in septic H9c2 cells by regulating the MAPK signaling pathway

Parecoxib, a non-steroidal anti-inflammatory drug, has been reported to possess protective effects against sepsis. However, its detailed role and underlying mechanisms in septic cardiomyopathy remain unclear. Therefore, the goal of the present study was to clarify the function and to investigate the mechanisms of parecoxib in lipopolysaccharide (LPS)-treated H9c2 rat cardiomyocytes. TNF-α, IL-1β and IL-6 expression levels in parecoxib-treated H9c2 cells stimulated with LPS were assessed using ELISA. Parecoxib-treated H9c2 cells stimulated with LPS were tested for viability using the Cell Counting Kit-8 assay. Western blotting analysis and 5-ethynyl-2'-deoxyuridine were used to evaluate cell proliferation. Apoptosis was assessed using TUNEL and western blotting. To assess the protein expression of the MAPK signaling pathway, western blotting was performed. The data showed that parecoxib significantly and dose-dependently reduced the inflammatory responses of LPS-treated H9c2 cells. Parecoxib also significantly and dose-dependently increased the proliferation and inhibited the apoptosis of LPS-treated H9c2 cells. In addition, parecoxib significantly suppressed the activation of the MAPK (p38, JNK and ERK) signaling pathway. The current study indicated that parecoxib could be a viable therapeutic option for septic cardiomyopathy.

CARDIOMYOCYTE REPROGRAMMING IN ANIMAL MODELS OF SEPTIC SHOCK

ABSTRACT

Cardiomyocyte reprogramming plays a pivotal role in sepsis-induced cardiomyopathy through the induction or overexpression of several factors and enzymes, ultimately leading to the characteristic decrease in cardiac contractility. The initial trigger is the binding of LPS to TLR-2, -3, -4, and -9 and of proinflammatory cytokines, such as TNF, IL-1, and IL-6, to their respective receptors. This induces the nuclear translocation of nuclear factors, such as NF-κB, via activation of MyD88, TRIF, IRAK, and MAPKs. Among the latter, ROS- and estrogen-dependent p38 and ERK 1/2 are proinflammatory, whereas JNK may play antagonistic, anti-inflammatory roles. Nuclear factors induce the synthesis of cytokines, which can amplify the inflammatory signal in a paracrine fashion, and of several effector enzymes, such as NOS-2, NOX-1, and others, which are ultimately responsible for the degradation of cardiomyocyte contractility. In parallel, the downregulation of enzymes involved in oxidative phosphorylation causes metabolic reprogramming, followed by a decrease in ATP production and the release of fragmented mitochondrial DNA, which may augment the process in a positive feedback loop. Other mediators, such as NO, ROS, the enzymes PI3K and Akt, and adrenergic stimulation may play regulatory roles, but not all signaling pathways that mediate cardiac dysfunction of sepsis do that by regulating reprogramming. Transcription may be globally modulated by miRs, which exert protective or amplifying effects. For all these mechanisms, differentiating between modulation of cardiomyocyte reprogramming versus systemic inflammation has been an ongoing but worthwhile experimental challenge.

In vivo evaluation of the protective effects of arjunolic acid against lipopolysaccharide-induced septic myocardial injury

Lipopolysaccharide (LPS) is a glycolipid component of the cell wall of Gram-negative bacteria, which induces multiple organ dysfunctions, eventually leading to septic shock and death. Arjunolic acid (AA) has been shown to have therapeutic benefits against various organ pathophysiologies, although its role in sepsis remains unclear. Here, we evaluated the effects of AA on LPS-induced free radical production and cardiotoxicity. Male albino mice were allocated to four groups: normal, 1.5 µg/30 g b.w. of LPS (LPS), 20 mg/kg b.w. AA with LPS (AA+LPS) and 20 mg/kg b.w. of AA (AA). Subsequently, blood and heart samples were harvested for biochemical and histopathological examinations. Pretreatment with AA attenuated LPS-induced increased serum levels of cardiac troponin I, lactate dehydrogenase and creatine kinase. In the meantime, AA pretreatment before LPS resulted in a significant increase in endogenous antioxidants (superoxide dismutase, catalase, glutathione peroxidase and reduced glutathione) and a significant decrease in the level of lipid peroxidation product (malondialdehyde) in the heart as compared to the LPS group, while cardiac cytochrome c activity were significantly increased. In addition, in the AA-pretreated mice, C-reactive protein and proinflammatory cytokines (interlukin-1 and tumor necrosis factor-alpha) were significantly reduced, and anti-inflammatory cytokines (interleukin-4 and -10) were significantly increased in cardiac tissues as compared to the LPS-treated animals. Furthermore, prior administration of AA to LPS exposed mice led to a significant a significant decrease in heart caspase-3, -8, and -9 as compared to the LPS group. Interestingly, AA was also able to improve LPS-induced histopathological changes in the cardiomyocytes. In conclusion, these in vivo findings indicate that AA may be a promising cardioprotective agent against LPS-stimulated cardiotoxicity, at least in part, through upregulation of cardiac antioxidants, reduction of lipid peroxidation, and inhibition of inflammation and cardiac cell death.

Energetic dysfunction in sepsis: a narrative review

Background

Growing evidence associates organ dysfunction(s) with impaired metabolism in sepsis. Recent research has increased our understanding of the role of substrate utilization and mitochondrial dysfunction in the pathophysiology of sepsis-related organ dysfunction. The purpose of this review is to present this evidence as a coherent whole and to highlight future research directions.

Main text

Sepsis is characterized by systemic and organ-specific changes in metabolism. Alterations of oxygen consumption, increased levels of circulating substrates, impaired glucose and lipid oxidation, and mitochondrial dysfunction are all associated with organ dysfunction and poor outcomes in both animal models and patients. The pathophysiological relevance of bioenergetics and metabolism in the specific examples of sepsis-related immunodeficiency, cerebral dysfunction, cardiomyopathy, acute kidney injury and diaphragmatic failure is also described.

Conclusions

Recent understandings in substrate utilization and mitochondrial dysfunction may pave the way for new diagnostic and therapeutic approaches. These findings could help physicians to identify distinct subgroups of sepsis and to develop personalized treatment strategies. Implications for their use as bioenergetic targets to identify metabolism- and mitochondria-targeted treatments need to be evaluated in future studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-021-00893-7.

CaMKII-dependent ryanodine receptor phosphorylation mediates sepsis-induced cardiomyocyte apoptosis

Sepsis is associated with cardiac dysfunction, which is at least in part due to cardiomyocyte apoptosis. However, the underlying mechanisms are far from being understood. Using the colon ascendens stent peritonitis mouse model of sepsis (CASP), we examined the subcellular mechanisms that mediate sepsis‐induced apoptosis. Wild‐type (WT) CASP mice hearts showed an increase in apoptosis respect to WT‐Sham. CASP transgenic mice expressing a CaMKII inhibitory peptide (AC3‐I) were protected against sepsis‐induced apoptosis. Dantrolene, used to reduce ryanodine receptor (RyR) diastolic sarcoplasmic reticulum (SR) Ca²⁺ release, prevented apoptosis in WT‐CASP. To examine whether CaMKII‐dependent RyR2 phosphorylation mediates diastolic Ca²⁺ release and apoptosis in sepsis, we evaluated apoptosis in mutant mice hearts that have the CaMKII phosphorylation site of RyR2 (Serine 2814) mutated to Alanine (S2814A). S2814A CASP mice did not show increased apoptosis. Consistent with RyR2 phosphorylation‐dependent enhancement in diastolic SR Ca²⁺ release leading to mitochondrial Ca²⁺ overload, mitochondrial Ca²⁺ retention capacity was reduced in mitochondria isolated from WT‐CASP compared to Sham and this reduction was absent in mitochondria from CASP S2814A or dantrolene‐treated mice. We conclude that in sepsis, CaMKII‐dependent RyR2 phosphorylation results in diastolic Ca²⁺ release from SR which leads to mitochondrial Ca²⁺ overload and apoptosis.

Exploring the pathophysiology of post-sepsis syndrome to identify therapeutic opportunities

Sepsis is a major health problem worldwide. As the number of sepsis cases increases, so does the number of sepsis survivors who suffer from “post-sepsis syndrome” after hospital discharge. This syndrome involves deficits in multiple systems, including the immune, cognitive, psychiatric, cardiovascular, and renal systems. Combined, these detrimental consequences lead to rehospitalizations, poorer quality of life, and increased mortality. Understanding the pathophysiology of these issues is crucial to develop new therapeutic opportunities to improve survival rate and quality of life of sepsis survivors. Such novel strategies include modulating the immune system and addressing mitochondrial dysfunction. A sepsis follow-up clinic may be useful to identify long-term health issues associated with post-sepsis syndrome and evaluate existing and novel strategies to improve the lives of sepsis survivors.

Resveratrol Protects the Myocardium in Sepsis by Activating the Phosphatidylinositol 3-Kinases (PI3K)/AKT/Mammalian Target of Rapamycin (mTOR) Pathway and Inhibiting the Nuclear Factor-κB (NF-κB) Signaling Pathway

Background

Sepsis combined with myocardial injury is an important cause of septic shock and multiple organ failure. However, the molecular mechanism of sepsis-induced myocardial dysfunction has not yet been thoroughly studied. Resveratrol has been an important research topic due its organ-protection function, but the specific mechanism is unclear. The purpose of this study was to explore the mechanism of organ injury in sepsis and to investigate the molecular mechanism of resveratrol in myocardial protection in sepsis.

Material/Methods

A classical Sprague-Dawley rat model of sepsis peritonitis was constructed for further experiments. The PI3K inhibitor LY294002 and resveratrol were used to intervene in a rat model of cardiomyopathy. HE staining was used to observe pathological changes. Cardiomyocyte apoptosis was detected by TUNEL assay. Western blot analysis was used to detect the level of maker proteins.

Results

The PI3K inhibitors could promote cardiac abnormalities and apoptosis, but resveratrol showed the opposite effect. The upregulation function of the PI3K inhibitor on the expression of NF-κB, IL-6, IL-1β, and TLR4 in LPS rats was not obvious, but the expression of TNF-α in LPS+LY294002 rats was increased by 22.85% compared with that in LPS rats (P<0.05). Compared with the LPS group, the expression of NF-κB, TNF-α, IL-6, IL-1β, and TLR4 in the LPS+resveratrol group was decreased. The expression of p-PI3K, p-AKT, and p-mTOR in LPS+LY294002 was reduced. The expression p-PI3K, p-AKT, and p-mTOR in the myocardium of the LPS+resveratrol group was increased.

Conclusions

Resveratrol can protect the myocardium in sepsis by activating the PI3K/AKT/mTOR signaling pathway and inhibiting the NF-κB signaling pathway and related inflammatory factors.

Molecular markers relevant to myocardial injury following dental extraction in patients with or without coronary artery disease

Objectives

The aim of this study was to characterize biological changes following dental extractions in patients with and without coronary artery disease (CAD).

Materials and methods

Forty-five patients (36 males and 9 females) referred for dental extraction underwent treatment and provided blood samples before, immediately after, and 24 h after the procedure. A broad array of biomarkers was employed to assess myocardial injury (highly sensitive troponin T, hs-TnT), bacterial burden (LPS endotoxin activity), and systemic inflammation (CRP, fibrinogen, IFN-γ, IL-1β, IL-6, IL-8, IL-10, IL-12, and TNF-α).

Results

Dental extraction in patients with and without CAD was associated with rises in hs-TnT (p = 0.013), hs-CRP (p < 0.001), fibrinogen (p = 0.005), endotoxin activity (p < 0.001), IFN-γ (p < 0.001), IL-6 (p < 0.001), IL-8 (p = 0.011), and IL-12 (p < 0.001) at 24 h compared with immediately post procedure. Changes in systemic inflammation and endotoxin activity were more evident in those with hs-TnT rise.

Conclusions

Simple dental extractions may cause mild increase in hs-TnT, indicating minor myocardial injury in both patients with and without CAD. Acute systemic inflammation and endotoxemia could represent a possible link between invasive dental treatment and increased risk of acute cardiovascular events. These findings indicate that invasive dental treatment (as simple as a single dental extraction) may impact negatively on clinical outcomes in dental patients, especially those with CAD.

Myocardial caspase-3 and NF-κB activation promotes calpain-induced septic apoptosis: The role of Akt/eNOS/NO pathway

AIMS

To explore the potential mechanism that the role of the Akt/eNOS/NO pathway in calpain-induced caspase-3 and NF-κB activation during septic apoptosis.

MAIN METHODS

Septic rats were stimulated by LPS (8 mg/kg, i.p.). Myocardial calpain, caspase-3, NO, TNF-α and IL-1β levels were detected by ELISA. The levels of Akt/p-Akt, eNOS/p-eNOS, iNOS proteins and number of apoptotic cells were evaluated by immunohistochemistry, western blot and TUNEL method.

KEY FINDINGS

Compared with sham, LPS treatment resulted in 4.1-fold and 1.8-fold increases in myocardial calpain activity and caspase-3 activation, respectively, and a significant increase (6.8-fold) in apoptotic cardiomyocytes was observed. The administration of calpain inhibitors (calpain inhibitor-IV, PD150606 and PD151746) showed that p-Akt and p-eNOS protein levels were correlated with the levels of LPS-induced myocardial calpain and caspase-3 activity. In addition, the quantity of p-Akt protein and NO content were markedly attenuated by wortmannin, a phosphoinositide 3-kinase (PI3K) inhibitor. Pretreatment with L-NAME, an NOS inhibitor, induced a decrease in p-eNOS proteins and apoptosis in myocardial tissues, while iNOS proteins were strongly increased in septic rats.

SIGNIFICANCE

This study suggests that the Akt/eNOS/NO pathway might lead to a novel pharmacological therapy for cardiomyocytes apoptosis in sepsis.

Adiponectin attenuates lipopolysaccharide-induced cell injury of H9c2 cells by regulating AMPK pathway

Adiponectin, an adipokine synthesized and secreted majorly by adipose tissue, is reported to exert cardioprotective properties via anti-inflammation and antiapoptosis. Lipopolysaccharide (LPS) is a common inflammation and apoptosis inducer of cardiomyocytes. However, few studies have reported the roles of adiponectin on LPS-induced inflammation as well as apoptosis of H9c2 cells, and the possible mechanisms of these effects. In the present study, we found that adiponectin significantly relieved LPS-induced cytotoxicity including decreased viability and elevated LDH release, inhibited LPS-triggered inflammation, which is evidenced by increases in release of TNF-α, IL-1β as well as IL-6, and attenuated the enhanced rates of apoptotic cells as well as increased caspase-3 activity caused by LPS in H9c2 cells. In addition, our data demonstrated that adiponectin upregulated AMP-activated protein kinase (AMPK) activation of H9c2 cells with or without LPS administration. Moreover, we found that blocking AMPK pathway by compound c attenuated the protective effects of adiponectin against the cytotoxicity, inflammatory response, and apoptosis of H9c2 cells resulted from LPS. Our observations bring novel insights for understanding the mediatory role of AMPK pathway implicated in the protective effects of adiponectin against LPS-induced cardiotoxicity.

Luteolin suppresses lipopolysaccharide‑induced cardiomyocyte hypertrophy and autophagy in vitro

Luteolin (LTL) serves essential roles in a wide variety of biological processes. Lipopolysaccharide (LPS) can lead to myocardial hypertrophy and autophagy. However, the roles of LTL on LPS-induced cardiomyocyte hypertrophy and autophagy in rat cardiomyocytes have not yet been fully elucidated. In the present study, the morphology of cultured rat cardiomyocytes was observed under an inverted microscope. Cell viability was detected by MTT assay. α-Actinin and microtubule-associated protein 1 light chain 3 (LC3) expression levels were measured by immunofluorescence assay. In addition, the expression levels of atrial natriuretic peptide/brain natriuretic peptide (ANP/BNP), LC3, and autophagy- and Wnt signaling pathway-associated genes were analyzed by reverse transcription-quantitative polymerase chain reaction or western blot assays. The results indicated that LTL increased the cell viability of cardiomyocytes treated with LPS. LTL decreased the expression of cardiac hypertrophy associated markers (ANP and BNP). LTL decreased α-actinin and LC3 expression levels in LPS-treated cardiomyocytes. It was also demonstrated that LTL suppressed the mRNA and protein expression levels of LPS-mediated autophagy and Wnt signaling pathway-associated genes. In addition, it was demonstrated that silencing of β-catenin inhibited LPS-induced cardiomyocyte hypertrophy and the formation of autophagosomes. Thus, the present study suggested that LTL protected against LPS-induced cardiomyocyte hypertrophy and autophagy in rat cardiomyocytes.

Simvastatin Protects Cardiomyocytes Against Endotoxin-induced Apoptosis and Up-regulates Survivin/NF-κB/p65 Expression

This study is aimed to investigate whether simvastatin induces cardiomyocytes survival signaling in endotoxin (lipopolysaccharide, LSP)-induced myocardial injury, and if so, further to determine a role of survivin in simvastatin-anti-apoptotic effect. Wistar rats were pretreated with simvastatin (10–40 mg/kg po) before a single non-lethal dose of LPS. In myocardial tissue, LPS induced structural disorganization of myofibrils with significant inflammatory infiltrate (cardiac damage score, CDS = 3.87 ± 0.51, p < 0.05), whereas simvastatin dose-dependently abolished structural changes induced by LPS (p < 0.01). Simvastatin in 20 mg/kg and 40 mg/kg pretreatment, dose dependently, attenuated myocardial apoptosis determined as apoptotic index (28.8 ± 4.5% and 18.9 ± 3.5, p < 0.05), decreased cleaved caspase-3 expression (32.1 ± 5.8%, p < 0.01), along with significant Bcl-xL expression in the simvastatin groups (p < 0.01). Interestingly, in the simvastatin groups were determined significantly increased expression of survivin (p < 0.01), but in negative correlation with cleaved caspase-3 and apoptotic indices (p < 0.01). Simvastatin has a cardioprotective effects against LPS induced apoptosis. The effect may be mediated by up-regulation of survivin via activation of NF-κB, which leads to reduced activation of caspase-3 and consequent apoptosis of cardiomyocytes in experimental sepsis.

Transplantation of CREG modified embryonic stem cells improves cardiac function after myocardial infarction in mice

Engraftment of embryonic stem cells (ESC) has been proposed as a potential therapeutic approach for post-infarction cardiac dysfunction. However, only mild function improvement has been achieved due to low survival rate and paracrine dysfunction of transplanted stem cells. Cellular repressor of E1A stimulated genes (CREG) has been reported to be a secreted glycoprotein implicated in promoting survival and differentiation of many cell types. Therefore we hypothesized that transplantation of genetically modified ESC with CREG (CREG-ESC) can improve cardiac function after myocardial infarction in mice. A total of 2 × 10⁵ CREG-ESC or EGFP-ESC were engrafted into the border zone in a myocardial infarction model in mice. Cardiac function, infarct size and fibrosis at 4 weeks, survival of transplanted ESC, apoptosis and cytokine level of heart tissue, and teratoma formation were assessed in vivo. Apoptosis of ESC under inflammatory stimuli and cardiac differentiation of ESC were investigated in vitro. After 4 weeks, we found transplantation of CREG-ESC could significantly improve cardiac function, ameliorate cardiac remodeling, and reduce infarct size and fibrosis area. Transplantation of CREG-ESC remarkably increased ESC survival in the border zone and inhibited apoptosis of cardiomyocytes. Furthermore, the decrease of inflammatory factors (IL-1β, IL-6 and TNF-α) and increase of anti-inflammatory factors (TGF-β, bFGF and VEGF165) in the border zone were higher in CREG-ESC transplanted hearts. Safety evaluation showed that all transplantation at 2 × 10⁵ per heart dose produced no teratoma. Surprisingly, the mice with 3.0 × 10⁶ CREG-ESC transplantation was demonstrated teratoma free without cardiac rhythm disturbances in contrast to 100% teratoma formation and rhythm abnormality for the same dose of EGFP-ESC transplantation. In addition, overexpression of CREG inhibits ESC apoptosis and enhanced their differentiation into cardiomyocytes in vitro. Transplantation of CREG-modified ESC exhibits a favorable survival pattern in infarcted hearts, which translates into a substantial preservation of cardiac function after acute myocardial infarction.

Quercetin exerts cardiovascular protective effects in LPS-induced dysfunction in vivo by regulating inflammatory cytokine expression, NF-κB phosphorylation, and caspase activity

Impaired myocardial contractile function, one of the well-documented features of sepsis, contributes greatly to the high rate of mortality. Quercetin is widely accepted as a potential antioxidant and free radical scavenger. Epidemiologic studies have suggested that an increase in the intake of dietary Quercetin can reduce the risk of cardiac disease. However, presently there is no report yet on the influence of Quercetin on LPS-induced myocardial dysfunction in vivo. Cardiovascular protective effects of Quercetin on LPS-induced sepsis in mice were measured after intragastric administration, using normal saline as a positive control. Quercetin pretreatment significantly alleviated LPS-induced cardiac abnormalities in mice. The histopathologic findings in the present study justify the findings reported from the biochemical analyses. Our observation from the present research work reveals that Quercetin suppressed the production of proinflammatory cytokines at different levels, such as TNF-α and IL-1β, and inhibits the activation of I-κB phosphorylation, whereas the total content was not affected. Apoptotic pathways are related to Quercetin protection in the development of myocardial dysfunction. In conclusion, our findings demonstrate the adjuvant potentials of Quercetin for clinical sepsis treatment.

Involvement of Mitochondrial Disorders in Septic Cardiomyopathy

Sepsis is defined as a life-threatening organ dysfunction caused by a dysregulated host response to infection. It remains a leading cause of death worldwide, despite the development of various therapeutic strategies. Cardiac dysfunction, also referred to as septic cardiomyopathy, is a frequent and well-described complication of sepsis and associated with worse clinical outcomes. Recent research has increased our understanding of the role of mitochondrial dysfunction in the pathophysiology of septic cardiomyopathy. The purpose of this review is to present this evidence as a coherent whole and to highlight future research directions.

Sepsis-Induced Cardiomyopathy: Oxidative Implications in the Initiation and Resolution of the Damage

Cardiac dysfunction may complicate the course of severe sepsis and septic shock with significant implications for patient's survival. The basic pathophysiologic mechanisms leading to septic cardiomyopathy have not been fully clarified until now. Disease-specific treatment is lacking, and care is still based on supportive modalities. Septic state causes destruction of redox balance in many cell types, cardiomyocytes included. The production of reactive oxygen and nitrogen species is increased, and natural antioxidant systems fail to counterbalance the overwhelming generation of free radicals. Reactive species interfere with many basic cell functions, mainly through destruction of protein, lipid, and nucleic acid integrity, compromising enzyme function, mitochondrial structure and performance, and intracellular signaling, all leading to cardiac contractile failure. Takotsubo cardiomyopathy may result from oxidative imbalance. This review will address the multiple aspects of cardiomyocyte bioenergetic failure in sepsis and discuss potential therapeutic interventions.

Improved Survival in a Long-Term Rat Model of Sepsis Is Associated With Reduced Mitochondrial Calcium Uptake Despite Increased Energetic Demand

OBJECTIVES

To investigate the relationship between prognosis, changes in mitochondrial calcium uptake, and bioenergetic status in the heart during sepsis.

DESIGN

In vivo and ex vivo controlled experimental studies.

SETTING

University research laboratory.

SUBJECTS

Male adult Wistar rats.

INTERVENTIONS

Sepsis was induced by intraperitoneal injection of fecal slurry. Sham-operated animals served as controls. Confocal microscopy was used to study functional and bioenergetic parameters in cardiomyocytes isolated after 24-hour sepsis. Electron microscopy was used to characterize structural changes in mitochondria and sarcoplasmic reticulum. The functional response to dobutamine was assessed in vivo by echocardiography.

MEASUREMENTS AND MAIN RESULTS

Peak aortic blood flow velocity measured at 24 hours was a good discriminator for 72-hour survival (area under the receiver operator characteristic, 0.84 ± 0.1; p = 0.03) and was used in ex vivo experiments at 24 hours to identify septic animals with good prognosis. Measurements from animals with good prognostic showed 1) a smaller increase in mitochondrial calcium content and in nicotinamide adenine dinucleotide fluorescence following pacing and 2) increased distance between mitochondria and sarcoplasmic reticulum on electron microscopy, and 3) nicotinamide adenine dinucleotide redox potential and adenosine triphosphate/adenosine diphosphate failed to reach a new steady state following pacing, suggesting impaired matching of energy supply and demand. In vivo, good prognosis animals had a blunted response to dobutamine with respect to stroke volume and kinetic energy.

CONCLUSIONS

In situations of higher energetic demand decreased mitochondrial calcium uptake may constitute an adaptive cellular response that confers a survival advantage in response to sepsis at a cost of decreased oxidative capacity.

Apelin Compared With Dobutamine Exerts Cardioprotection and Extends Survival in a Rat Model of Endotoxin-Induced Myocardial Dysfunction

OBJECTIVE

Dobutamine is the currently recommended β-adrenergic inotropic drug for supporting sepsis-induced myocardial dysfunction when cardiac output index remains low after preload correction. Better and safer therapies are nonetheless mandatory because responsiveness to dobutamine is limited with numerous side effects. Apelin-13 is a powerful inotropic candidate that could be considered as an alternative noncatecholaminergic support in the setting of inflammatory cardiovascular dysfunction.

DESIGN

Interventional controlled experimental animal study.

SETTING

Tertiary care university-based research institute.

SUBJECTS

One hundred ninety-eight adult male rats.

INTERVENTIONS

Using a rat model of "systemic inflammation-induced cardiac dysfunction" induced by intraperitoneal lipopolysaccharide injection (10 mg/kg), hemodynamic efficacy, cardioprotection, and biomechanics were assessed under IV osmotic pump infusions of apelin-13 (0.25 μg/kg/min) or dobutamine (7.5 μg/kg/min).

MEASUREMENTS AND MAIN RESULTS

In this model and in both in vivo and ex vivo studies, apelin-13 compared with dobutamine provoked distinctive effects on cardiac function: 1) optimized cardiac energy-dependent workload with improved cardiac index and lower vascular resistance, 2) upgraded hearts' apelinergic responsiveness, and 3) consecutive downstream advantages, including increased urine output, enhanced plasma volume, reduced weight loss, and substantially improved overall outcomes. In vitro studies confirmed that these apelin-13-driven processes encompassed a significant and rapid reduction in systemic cytokine release with dampening of myocardial inflammation, injury, and apoptosis and resolution of associated molecular pathways.

CONCLUSIONS

In this inflammatory cardiovascular dysfunction, apelin-13 infusion delivers distinct and optimized hemodynamic support (including positive fluid balance), along with cardioprotective effects, modulation of circulatory inflammation and extended survival.

Sepsis-induced cardiac dysfunction and β-adrenergic blockade therapy for sepsis

Despite recent advances in medical care, mortality due to sepsis, defined as life-threatening organ dysfunction caused by a dysregulated host response to infection, remains high. Fluid resuscitation and vasopressors are the first-line treatment for sepsis in order to optimize hemodynamic instability caused by vasodilation and increased vascular permeability. However, these therapies, aimed at maintaining blood pressure and blood flow to vital organs, could have deleterious cardiac effects, as cardiomyocyte damage occurs in the early stages of sepsis. Recent experimental and clinical studies have demonstrated that a number of factors contribute to sepsis-induced cardiac dysfunction and the degree of cardiac dysfunction is one of the major prognostic factors of sepsis. Therefore, strategies to prevent further cardiomyocyte damage could be of crucial importance in improving the outcome of sepsis. Among many factors causing sepsis-induced cardiac dysfunction, sympathetic nerve overstimulation, due to endogenous elevated catecholamine levels and exogenous catecholamine administration, is thought to play a major role. β-adrenergic blockade therapy is widely used for ischemic heart disease and chronic heart failure and in the prevention of cardiovascular events in high-risk perioperative patients undergoing major surgery. It has also been shown to restore cardiac function in experimental septic animal models. In a single-center randomized controlled trial, esmolol infusion in patients with septic shock with persistent tachycardia reduced the 28-day mortality. Furthermore, it is likely that β-adrenergic blockade therapy may result in further beneficial effects in patients with sepsis, such as the reduction of inflammatory cytokine production, suppression of hypermetabolic status, maintenance of glucose homeostasis, and improvement of coagulation disorders. Recent accumulating evidence suggests that β-adrenergic blockade could be an attractive therapy to improve the prognosis of sepsis. We await a large multicenter randomized clinical trial to confirm the beneficial effects of β-adrenergic blockade therapy in sepsis, of which mortality is still high.

Sarcolemmal ATP-sensitive potassium channel protects cardiac myocytes against lipopolysaccharide-induced apoptosis

The sarcolemmal ATP-sensitive K⁺ (sarcK_ATP) channel plays a cardioprotective role during stress. However, the role of the sarcK_ATP channel in the apoptosis of cardiomyocytes and association with mitochondrial calcium remains unclear. For this purpose, we developed a model of LPS-induced sepsis in neonatal rat cardiomyocytes (NRCs). The TUNEL assay was performed in order to detect the apoptosis of cardiac myocytes and the MTT assay was performed to determine cellular viability. Exposure to LPS significantly decreased the viability of the NRCs as well as the expression of Bcl-2, whereas it enhanced the activity and expression of the apoptosis-related proteins caspase-3 and Bax, respectively. The sarcK_ATP channel blocker, HMR-1098, increased the apoptosis of NRCs, whereas the specific sarcK_ATP channel opener, P-1075, reduced the apoptosis of NRCs. The mitochondrial calcium uniporter inhibitor ruthenium red (RR) partially inhibited the pro-apoptotic effect of HMR-1098. In order to confirm the role of the sarcK_ATP channel, we constructed a recombinant adenovirus vector carrying the sarcK_ATP channel mutant subunit Kir6.2AAA to inhibit the channel activity. Kir6.2AAA adenovirus infection in NRCs significantly aggravated the apoptosis of myocytes induced by LPS. Elucidating the regulatory mechanisms of the sarcK_ATP channel in apoptosis may facilitate the development of novel therapeutic targets and strategies for the management of sepsis and cardiac dysfunction.

Endotoxemia Engages the RhoA Kinase Pathway to Impair Cardiac Function By Altering Cytoskeleton, Mitochondrial Fission, and Autophagy

AIMS

The RhoA/ROCK pathway controls crucial biological processes involved in cardiovascular pathophysiology, such as cytoskeleton dynamics, vascular smooth muscle contraction, and inflammation. In this work, we tested whether Rho kinase inhibition would beneficially impact cardiac cytoskeleton organization, bioenergetics, and autophagy in experimental endotoxemia induced by lipopolysaccharides (LPSs) in mice.

RESULTS

Fasudil, a potent ROCK inhibitor, prevented LPS-induced cardiac inflammation, oxidative stress, cytoskeleton disarray, and mitochondrial injury. ROCK inhibition prevented phosphorylation of cofilin and dynamin-related protein-1, which promotes stabilization-polymerization of F-actin and mediates mitochondrial fission, respectively. Pyr1, which exclusively alters actin dynamics, prevented LPS-induced myocardial dysfunction, suggesting that beneficial impact of ROCK inhibition was not mainly related to pleiotropic effects of fasudil on cardiac inflammation and oxidative stress. Fasudil reduced mitochondrial fragmentation, stimulated initiation of autophagy, and elicited cardioprotection in LPS heart. Mdivi-1, a potent mitochondria fission inhibitor, converted cardioprotective autophagy to an inefficient form due to cargo loading failure in which autophagic vacuoles fail to trap cytosolic cargo, despite their formation at enhanced rates and lysosomal elimination.

INNOVATION

In experimental endotoxemia, cardioprotection by RhoA/ROCK inhibition may be related to changes in actin cytoskeleton reorganization and mitochondrial homeostasis. Improvement of LPS-induced mitochondrial dysfunction by fasudil was attributed to inhibition of ROCK-dependent Drp1 phosphorylation and activation of autophagic processes that can limit mitochondrial fragmentation and enhance degradation of damaged mitochondria, respectively.

CONCLUSION

Fasudil prevented LPS-induced heart oxidative stress, abnormal F-actin distribution, and oxidative phosphorylation, which concur to improve cardiac contractile and bioenergetic function. We suggest that fasudil may represent a valuable therapy for patients with sepsis.

Dietary Apigenin Exerts Immune-Regulatory Activity in Vivo by Reducing NF-κB Activity, Halting Leukocyte Infiltration and Restoring Normal Metabolic Function

The increasing prevalence of inflammatory diseases and the adverse effects associated with the long-term use of current anti-inflammatory therapies prompt the identification of alternative approaches to reestablish immune balance. Apigenin, an abundant dietary flavonoid, is emerging as a potential regulator of inflammation. Here, we show that apigenin has immune-regulatory activity in vivo. Apigenin conferred survival to mice treated with a lethal dose of Lipopolysaccharide (LPS) restoring normal cardiac function and heart mitochondrial Complex I activity. Despite the adverse effects associated with high levels of splenocyte apoptosis in septic models, apigenin had no effect on reducing cell death. However, we found that apigenin decreased LPS-induced apoptosis in lungs, infiltration of inflammatory cells and chemotactic factors’ accumulation, re-establishing normal lung architecture. Using NF-κB luciferase transgenic mice, we found that apigenin effectively modulated NF-κB activity in the lungs, suggesting the ability of dietary compounds to exert immune-regulatory activity in an organ-specific manner. Collectively, these findings provide novel insights into the underlying immune-regulatory mechanisms of dietary nutraceuticals in vivo.

CYP-epoxygenase metabolites of docosahexaenoic acid protect HL-1 cardiac cells against LPS-induced cytotoxicity Through SIRT1

Bacterial LPS is an environmental toxin capable of promoting various cardiac complications. Current evidence suggests that LPS-induced myocardial dysfunction emerges as a consequence of compromised quality of cardiac mitochondria. Docosahexaenoic acid (DHA, 22:6n3) is an n-3 polyunsaturated fatty acid (PUFA), which produces a broad spectrum of intrinsic physiological effects including regulation of cell survival and death mechanisms. Although, numerous studies revealed fundamentally beneficial effects of DHA on cardiovascular system, it remains unknown whether these effects were produced by DHA or one of its possibly more potent metabolites. Emerging evidence indicates that cytochrome P450 (CYP) epoxygenase metabolites of DHA, epoxydocosapentaenoic acids (EDPs), produce more potent biological activity compared to its precursor DHA. In this study, we investigated whether DHA and its metabolite 19,20-EDP could protect HL-1 cardiac cells against LPS-induced cytotoxicity. We provide evidence that exogenously added or DHA-derived EDPs promote mitochondrial biogenesis and function in HL-1 cardiac cells. Our results illustrate the CYP epoxygenase metabolite of DHA, 19,20-EDP, confers extensive protection to HL-1 cardiac cells against LPS-induced cytotoxicity via activation of SIRT1.

Role of endogenous TNF-α in cardiomyocyte apoptosis induced by bacteria lipoprotein and the protective effect of IL-10

Cardiomyocyte apoptosis is thought to play an important role in sepsis-induced cardiodepression. Previous studies mainly focused on the role of exogenous TNF-α in sepsis-induced cardiac damage, however, the role of endogenous TNF-α is rarely known. Therefore, we hypothesized that endogenous TNF-α also contributed to sepsis-induced cardiomyocyte apoptosis. Primary neonatal rat cardiomyocytes were time- and dose-dependently stimulated with BLP and TNF-α. In separate experiments, cells were treated with TNF-α antagonist and IL-10, respectively, to determine effects of endogenous TNF-α and exogenous IL-10 on BLP-induced cardiomyocyte apoptosis. After treatment, apoptosis was evaluated by nuclear condensation, membrane permeability change, caspase-3 activation, and pro- to anti-apoptotic protein (bax to bcl-2) expression. Treatment of cardiomyocytes with BLP and TNF-α both significantly induced caspase-3 activation in a time- and dose-dependent manner and caused apparent nuclear condensation and increased membrane permeability. TNF-α antagonist pretreatment attenuated BLP-induced caspase-3 activation, and downregulated bax/bcl-2 ratio. In addition, administration of IL-10 inhibited TNF-α production and suppressed cardiomyocyte apoptosis induced by BLP. Our data suggest that endogenous TNF-α play an important role in BLP-induced cardiomyocyte apoptosis and IL-10 protect cardiomyocytes from BLP-induced apoptosis, an effect partially through inhibition of endogenous TNF-α production.

Dysregulation of intracellular calcium transporters in animal models of sepsis-induced cardiomyopathy

Sepsis-induced cardiomyopathy (SIC) develops as the result of myocardial calcium (Ca) dysregulation. Here we reviewed all published studies that quantified the dysfunction of intracellular Ca transporters and the myofilaments in animal models of SIC. Cardiomyocytes isolated from septic animals showed, invariably, a decreased twitch amplitude, which is frequently caused by a decrease in the amplitude of cellular Ca transients (ΔCai) and sarcoplasmic reticulum (SR) Ca load (CaSR). Underlying these deficits, the L-type Ca channel is downregulated, through mechanisms that may involve adrenomedullin-mediated redox signaling. The SR Ca pump is also inhibited, through oxidative modifications (sulfonylation) of one reactive thiol group (on Cys) and/or modulation of phospholamban. Diastolic Ca leak of ryanodine receptors is frequently increased. In contrast, Na/Ca exchange inhibition may play a partially compensatory role by increasing CaSR and ΔCai. The action potential is usually shortened. Myofilaments show a bidirectional regulation, with decreased Ca sensitivity in milder forms of disease (due to troponin I hyperphosphorylation) and an increase (redox mediated) in more severe forms. Most deficits occurred similarly in two different disease models, induced by either intraperitoneal administration of bacterial lipopolysaccharide or cecal ligation and puncture. In conclusion, substantial cumulative evidence implicates various Ca transporters and the myofilaments in SIC pathology. What is less clear, however, are the identity and interplay of the signaling pathways that are responsible for Ca transporters dysfunction. With few exceptions, all studies we found used solely male animals. Identifying sex differences in Ca dysregulation in SIC becomes, therefore, another priority.

β₁-adrenoceptor stimulation promotes LPS-induced cardiomyocyte apoptosis through activating PKA and enhancing CaMKII and IκBα phosphorylation

INTRODUCTION

Caspase activation and cardiomyocyte apoptosis have been implicated in lipopolysaccharide (LPS)-induced cardiac contractile dysfunction. We have recently demonstrated that β1-adrenoceptor (AR) activation by endogenous norepinephrine contributes to cardiomyocyte apoptosis in endotoxemic mice. Here, we further investigated the molecular mechanisms for the enhancing effect of β₁-AR activation on LPS-induced cardiomyocyte apoptosis.

METHODS

The adult mouse ventricular myocytes were exposed to LPS, dobutamine, protein kinase A (PKA) inhibitor or/and nifedipine, an L-type Ca(2+) channel blocker. Male BALB/c mice were treated with LPS or/ and β₁-AR antagonist, atenolol. Cardiomyocyte apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling (TUNEL) assay and apoptosis-associated molecules were detected.

RESULTS

LPS induced apoptosis in adult mouse ventricular myocytes, dobutamine (DOB), a β₁-AR agonist, promoted apoptosis, caspase-8, 9 and 3 activation and increased cytosolic Ca(2+) concentration in LPS-challenged cardiomyocytes. DOB also up-regulated TNF-α expression, decreased Bcl-2 levels, promoted Bax translocation to mitochondria, mitochondrial membrane potential loss and cytochrome c release as well as IκBα, p38 MAPK, JNK and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) phosphorylation in LPS-treated cardiomyocytes. PKA inhibitor abolished the effects of DOB on caspase-9 activation, Bcl-2 levels as well as JNK and p38 MAPK phosphorylation, but not on IκBα phosphorylation, TNF-α expression and caspase-8 activation in LPS-stimulated cardiomyocytes. Pretreatment with nifedipine not only significantly blocked the enhancing effects of DOB on LPS-induced elevation in cytosolic Ca(2+) concentration and CaMKII phosphorylation in cardiomyocytes, but also partly reversed the effects of DOB on caspase-9 and caspase-3/7 activities in LPS-treated cardiomyocytes. Furthermore, atenolol suppressed TNF-α expression, JNK, p38 MAPK and CaMKII phosphorylation, increased Bcl-2 expression, and inhibited cytochrome c release and cardiomyocyte apoptosis in the myocardium of endotoxemic mice.

CONCLUSIONS

β1-AR activation promotes LPS-induced apoptosis through activating PKA, increasing CaMKII phosphorylation as well as enhancing IκBα phosphorylation and TNF-α expression in cardiomyocytes.

Lipopolysaccharide and cytokines inhibit rat cardiomyocyte contractility in vitro

BACKGROUND

Sepsis-induced cardiomyopathy (SIC) is thought to be the result of detrimental effects of inflammatory mediators on the cardiac muscle. Here we studied the effects of prolonged (24 ± 4 h) exposure of adult rat ventricular myocytes (ARVM) to bacterial lipopolysaccharide (LPS) and inflammatory cytokines tumor necrosis factor (TNF) and interleukins-1 (IL-1) and IL-6.

MATERIALS AND METHODS

We measured sarcomere shortening (SS) and cellular calcium (Ca(2+)) transients (ΔCai, with fura-2 AM) in isolated cardiomyocytes externally paced at 5 Hz at 37°C.

RESULTS

SS decreased after incubation with LPS (100 μg/mL), IL-1 (100 ng/mL), and IL-6 (30 ng/mL), but not with lesser doses of these mediators, or TNF (10-100 ng/mL). A combination of LPS (100 μg/mL), TNF, IL-1, and IL-6 (each 100 ng/mL; i.e., "Cytomix-100") induced a maximal decrease in SS and ΔCai. Sarcoplasmic reticulum (SR) Ca(2+) load (CaSR, measured with caffeine) was unchanged by Cytomix-100; however, SR fractional release (ΔCai/CaSR) was decreased. Underlying these effects, Ca(2+) influx into the cell (via L-type Ca(2+) channels, LTCC) and Ca(2+) extrusion via Na(+)/Ca(2+) exchange were decreased by Cytomix-100. SR Ca(2+) pump (SERCA) (SR Ca(2+) ATPase) was not affected.

CONCLUSIONS

Prolonged exposure of ARVM to a mixture of LPS and inflammatory cytokines inhibits cell contractility. The effect is mediated by the inhibition of Ca(2+) influx via LTCC, and partially opposed by the inhibition of Na(+)/Ca(2+) exchange. Because both mechanisms are commonly seen in animal models of SIC, we conclude that prolonged challenge with Cytomix-100 of ARVM may represent an accurate in vitro model for SIC.

Baicalein Inhibits HMGB1 Release and MMP-2/-9 Expression in Lipopolysaccharide-Induced Cardiac Hypertrophy

Myocardial dysfunction, a common complication after sepsis, significantly contributes to the death of patients with septic shock. In the search for potentially effective drugs to decrease mortality from sepsis, we investigated the cardioprotective effects of baicalein, a flavonoid present in the root of Scutellaria baicalensis, on lipopolysaccharide (LPS)-induced pro-inflammatory cytokine production and matrix metalloproteinase-2 and -9 (MMP-2/-9) expression. We found that baicalein significantly attenuated LPS-induced cardiac hypertrophy and counteracted reactive oxygen species (ROS) generation in neonatal rat cardiomyocytes. In addition, pretreatment with baicalein inhibited LPS-induced early (e.g., tumor necrosis factor-α (TNF-α) and interleukin-6) and late (e.g., high mobility group box 1 (HMGB1) pro-inflammatory cytokine release, inducible nitric oxide synthase (iNOS) expression and NO production. Finally, baicalein also significantly down-regulated the expression of MMP-2/-9 and attenuated HMGB1 translocation from the nucleus to the cytoplasm. These results suggest that baicalein can protect cardiomyocytes from LPS-induced cardiac injury via the inhibition of ROS and inflammatory cytokine production. These cardioprotective effects are possibly mediated through the inhibition of the HMGB1 and MMP-2/-9 signaling pathways.

Cardiac troponin in ischemic cardiomyocytes: intracellular decrease before onset of cell death

AIM

Cardiac troponin I (cTnI) and T (cTnT) are the most important biomarkers in the diagnosis of acute myocardial infarction (AMI). Nevertheless, they can be elevated in the absence of AMI. It is unclear if such elevations represent irreversible cardiomyocyte-damage or leakage from viable cardiomyocytes. Our objective is to evaluate whether cTn is released from viable cardiomyocytes in response to ischemia and to identify differences in the release of cTn and its molecular forms.

METHODS AND RESULTS

HL-1 cardiomyocytes (mouse) were subjected to ischemia (modeled by anoxia with glucose deprivation). The total contents and molecular forms of cTn were determined in culture media and cell lysates. Cell viability was assessed from the release of lactate dehydrogenase (LDH). Before the release of LDH, the intracellular cTn content in ischemic cells decreased significantly compared to control (52% for cTnI; 23% for cTnT) and was not matched by a cTn increase in the medium. cTnI decreased more rapidly than cTnT, resulting in an intracellular cTnT/cTnI ratio of 25.5 after 24 h of ischemia. Western blots revealed changes in the relative amounts of fragmented cTnI and cTnT in ischemic cells.

CONCLUSIONS

HL-1 cardiomyocytes subjected to simulated ischemia released cTnI and cTnT only in combination with the release of LDH. We find no evidence of cTn release from viable cardiomyocytes, but did observe a significant decrease in cTn content, before the onset of cell death. Intracellular decrease of cTn in viable cardiomyocytes can have important consequences for the interpretation of cTn values in clinical practice.

Macrophage migration inhibitory factor induces contractile and mitochondria dysfunction by altering cytoskeleton network in the human heart

OBJECTIVES

Macrophage migration inhibitory factor (MIF) has been recognized as a potent proinflammatory mediator that may induce myocardial dysfunction. Mechanisms by which MIF affects cardiac function are not completely elucidated; yet, some macrophage migration inhibitory effects have been related to changes in cytoskeleton architecture. We hypothesized that MIF-induced myocardial dysfunction and mitochondrial respiration deficit could be related to cardiac cell microtubule dynamics alterations.

DESIGN

Prospective, randomized study.

SETTING

Experimental Cardiovascular Laboratory, University Hospital.

SUBJECTS

Human myocardial (atrial) trabeculae.

INTERVENTIONS

Atrial trabeculae were obtained at the time of cardiac surgery. Isometrically contracting isolated human right atrial trabeculae were exposed to MIF (100 ng/mL) for 60 minutes, in the presence or not of pretreatment with colchicine (10 µM), a microtubule-depolymerizing agent, or paclitaxel (10 µM) a microtubule-stabilizing agent.

MEASUREMENTS AND MAIN RESULTS

Maximal active isometric tension curve and developed isometric force were studied. Trabeculae were then permeabilized for mitochondrial respiration studies using high-resolution oxygraphy. Heart fiber electron microscopy and visualization of βIV tubulin and polymerized actin by confocal microscopy were used to evaluate sarcomere and microtubule disarray. Compared with controls, MIF elicited cardiac contractile and mitochondrial dysfunction, which were largely prevented by pretreatment with colchicine, but not by paclitaxel. Pretreatment with colchicine prevented MIF-induced microtubule network disorganization, excessive tubulin polymerization, and mitochondrial fragmentation. Compound-C, an inhibitor of AMP-activated protein kinase (AMPK), partially prevented contractile dysfunction, suggesting that cardiac deleterious effects of MIF were related to AMPK activation.

CONCLUSIONS

MIF depresses human myocardial contractile function and impairs mitochondrial respiration. Changes in microtubule network likely promote MIF-induced cardiac dysfunction by 1) altering with mitochondrial tubular assembly and outer membrane permeability for adenine nucleotides leading to energy deficit, 2) excessive tubulin polymerization that may impede cardiomyocyte viscosity and motion, and 3) interfering with AMPK pathway.

Role of Kir6.2 subunits of ATP-sensitive potassium channels in endotoxemia-induced cardiac dysfunction

Background

Cardiac dysfunction is well-described in endotoxemia and diagnosed in up to 60% of patients with endotoxic shock. ATP-sensitive potassium (K_ATP) channels are critical to cardiac function. This study investigates the role of Kir6.2 subunits of K_ATP channels on cardiac dysfunction in lipopolysaccharide (LPS)-induced endotoxemia.

Methods

Kir6.2 subunits knockout (Kir6.2^−/−) and wild-type (WT) mice were injected with LPS to induce endotoxemia. Cardiac function was monitored by echocardiography. Left ventricles were taken for microscopy (both light and electron) and TUNEL examination. Serum lactate dehydrogenase (LDH) and creatine kinase (CK) activities, and tumor necrosis factor-α (TNF-α) levels in both serum and left ventricular tissues were determined.

Results

Compared to WT, Kir6.2^−/− mice showed significantly declined cardiac function 360 min after LPS administration, aggravated myocardial damage and elevated serum LDH and CK activities. Apoptotic cells were obviously increased in heart tissues from Kir6.2^−/− mice at 90, 180 and 360 min. TNF-α expression in both serum and heart tissues of Kir6.2^−/− mice was significantly increased.

Conclusions

We conclude that Kir6.2 subunits are critical in resistance to endotoxemia-induced cardiac dysfunction through reducing myocardial damage by inhibition of apoptosis and inflammation. K_ATP channels blockers are extensively used in the treatment of diabetes, their potential role should therefore be considered in the clinic when patients treated with antidiabetic sulfonylureas are complicated by endotoxemia.

The role of the Hsp90/Akt pathway in myocardial calpain-induced caspase-3 activation and apoptosis during sepsis

Background

Recent studies have demonstrated that myocardial calpain triggers caspase-3 activation and myocardial apoptosis in models of sepsis, whereas the inhibition of calpain activity down-regulates myocardial caspase-3 activation and apoptosis. However, the mechanism underlying this pathological process is unclear. Therefore, in this study, our aim was to explore whether the Hsp90/Akt signaling pathway plays a role in the induction of myocardial calpain activity, caspase-3 activation and apoptosis in the septic mice.

Methods

Adult male C57 mice were injected with lipopolysaccharide (LPS, 4 mg/kg, i.p.) to induce sepsis. Next, myocardial caspase-3 activity and the levels of Hsp90/p-Akt (phospho-Akt) proteins were detected, and apoptotic cells were assessed by performing the TUNEL assay.

Results

In the septic mice, there was an increase in myocardial calpain and caspase-3 activity in addition to an increase in the number of apoptotic cells; however, there was a time-dependent decrease in myocardial Hsp90/p-Akt protein levels. The administration of calpain inhibitors (calpain inhibitor-Ш or PD150606) prevented the LPS-induced degradation of myocardial Hsp90/p-Akt protein and its expression in cardiomyocytes in addition to inhibiting myocardial caspase-3 activation and apoptosis. The inhibition of Hsp90 by pretreatment with 17-AAG induced p-Akt degradation, and the inhibition of Akt activity by pretreatment with wortmannin resulted in caspase-3 activation in wildtype C57 murine heart tissues.

Conclusions

Myocardial calpain induces myocardial caspase-3 activation and apoptosis in septic mice via the activation of the Hsp90/Akt pathway.

Reduction of cardiomyocyte S-nitrosylation by S-nitrosoglutathione reductase protects against sepsis-induced myocardial depression

Myocardial depression is an important contributor to morbidity and mortality in septic patients. Nitric oxide (NO) plays an important role in the development of septic cardiomyopathy, but also has protective effects. Recent evidence has indicated that NO exerts many of its downstream effects on the cardiovascular system via protein S-nitrosylation, which is negatively regulated by S-nitrosoglutathione reductase (GSNOR), an enzyme promoting denitrosylation. We tested the hypothesis that reducing cardiomyocyte S-nitrosylation by increasing GSNOR activity can improve myocardial dysfunction during sepsis. Therefore, we generated mice with a cardiomyocyte-specific overexpression of GSNOR (GSNOR-CMTg mice) and subjected them to endotoxic shock. Measurements of cardiac function in vivo and ex vivo showed that GSNOR-CMTg mice had a significantly improved cardiac function after lipopolysaccharide challenge (LPS, 50 mg/kg) compared with wild-type (WT) mice. Cardiomyocytes isolated from septic GSNOR-CMTg mice showed a corresponding improvement in contractility compared with WT cells. However, systolic Ca(2+) release was similarly depressed in both genotypes after LPS, indicating that GSNOR-CMTg cardiomyocytes have increased Ca(2+) sensitivity during sepsis. Parameters of inflammation were equally increased in LPS-treated hearts of both genotypes, and no compensatory changes in NO synthase expression levels were found in GSNOR-overexpressing hearts before or after LPS challenge. GSNOR overexpression however significantly reduced total cardiac protein S-nitrosylation during sepsis. Taken together, our results indicate that increasing the denitrosylation capacity of cardiomyocytes protects against sepsis-induced myocardial depression. Our findings suggest that specifically reducing protein S-nitrosylation during sepsis improves cardiac function by increasing cardiac myofilament sensitivity to Ca(2+).

Sepsis-induced cardiomyopathy

Myocardial dysfunction is one of the main predictors of poor outcome in septic patients, with mortality rates next to 70%. During the sepsis-induced myocardial dysfunction, both ventricles can dilate and diminish its ejection fraction, having less response to fluid resuscitation and catecholamines, but typically is assumed to be reversible within 7-10 days. In the last 30 years, It´s being subject of substantial research; however no explanation of its etiopathogenesis or effective treatment have been proved yet. The aim of this manuscript is to review on the most relevant aspects of the sepsis-induced myocardial dysfunction, discuss its clinical presentation, pathophysiology, etiopathogenesis, diagnostic tools and therapeutic strategies proposed in recent years.

The effects of apoptosis vulnerability markers on the myocardium in depression after myocardial infarction

BACKGROUND

There is an increased incidence of major depressive disorder (MDD) in individuals after myocardial infarction (MI), but the pathophysiological processes mediating this association are unclear. Our previous study demonstrated an increase in pro-apoptotic pathways in the myocardium and hippocampus in MDD, which was reversed by venlafaxine. This study aimed to attempt to confirm the effects of apoptosis vulnerability markers on the myocardium in a model of depression after myocardial infarction.

METHODS

Rats were divided into four groups: sham (N = 8), depression (N = 8, chronic mild unpredictable stress and separation were used in the depression group), MI (N = 13) and post-MI depression (N = 7). The rats in all four groups underwent the same open field and sucrose preference behavioral tests. Evan Blue staining was used to determine the area at risk of myocardial infarction in the left ventricle, and 2,3,5-triphenyl tetrazolium chloride (1.5% TTC) dye was used to detect the size of the myocardial infarction. The expression of bax and bcl-2 protein in the myocardium was investigated by immunohistochemistry, and the mRNA expression of bax, bcl-2 and caspase-3 in the myocardium was investigated by real time RT-PCR. Apoptosis was estimated in the myocardium by measuring the Bax:Bcl-2 ratio.

RESULTS

In the depression and post-MI depression rats, there were significantly decreased movements and total sucrose consumption, modeling behavioral deficits and an anhedonic-like state. In terms of myocardial infarction size, no difference was seen between the MI and post-MI depression groups. There was an up-regulated Bax:Bcl-2 ratio in the depression, MI and post-MI depression groups. Furthermore, in the latter group, there was a greater up-regulated Bax:Bcl-2 ratio. However, caspase-3 did not differ among the four groups.

CONCLUSIONS

These results of this animal model suggest that active pro-apoptotic pathways may be involved in the nexus between myocardial infarction and depression. This mechanism may be germane to understanding this relationship in humans.

Yohimbine promotes cardiac NE release and prevents LPS-induced cardiac dysfunction via blockade of presynaptic α2A-adrenergic receptor

Myocardial depression is an important contributor to mortality in sepsis. We have recently demonstrated that α2-adrenoceptor (AR) antagonist, yohimbine (YHB), attenuates lipopolysaccharide (LPS)-induced myocardial depression. However, the mechanisms for this action of YHB are unclear. Here, we demonstrated that YHB decreased nitric oxide (NO) and tumor necrosis factor-alpha (TNF-α) levels in the myocardium and plasma, attenuated cardiac and hepatic dysfunction, but not kidney and lung injuries in endotoxemic mice. Immunohistochemical analysis revealed that cardiac α2A-AR was mostly located in sympathetic nerve presynaptic membrane; YHB decreased cardiac α2A-AR level and promoted cardiac norepinephrine (NE) release in endotoxemic mice. Reserpine that exhausted cardiac NE without markedly decreasing plasma NE level abrogated the inhibitory effects of YHB on cardiac TNF-α and iNOS expression as well as cardiac dysfunction, but not the suppressive effects of YHB on plasma TNF-α and NO elevation in LPS-challenged mice. Furthermore, both reserpine and YHB significantly inhibited LPS-induced myocardial apoptosis. α1-AR, β2-AR, but not β1-AR antagonists reversed the inhibitory effect of YHB on LPS-stimulated myocardial apoptosis. However, β1-AR antagonist attenuated LPS-caused cardiomyocyte apoptosis, partly abolished the protective effect of YHB on the left ventricular ejection fraction in endotoxemic mice. Altogether, these findings indicate that YHB attenuates LPS-induced cardiac dysfunction, at least in part, through blocking presynaptic α2A-AR and thus increasing cardiac NE release. YHB-elevated cardiac NE improves cardiac function via suppressing cardiac iNOS and TNF-α expression, activating β1-AR and inhibiting cardiomyocyte apoptosis through α1- and β2-AR in endotoxemic mice. However, cardiac β1-AR activation promotes LPS-induced cardiomyocyte apoptosis.

Resuscitation fluids and endotoxin-induced myocardial dysfunction: is selection a load-independent differential issue?

Along with redistributive shock, myocardial dysfunction is now recognized as highly prevalent in early severe sepsis. Indeed, aside from their distinct loading potency, resuscitation fluids have been poorly investigated as to their specific molecular impact on myocardial dysfunction. The objective of this study was to evaluate the load-independent biological impact of different resuscitation fluids on endotoxin-induced myocardial dysfunction. Adult rats implanted with a central venous catheter were given an intraperitoneal injection of endotoxin (lipopolysaccharides [LPSs], Escherichia coli, 10 mg/kg) or normal saline (sham) and subsequently infused or not with similar "fluid potency" loading resuscitation fluid (normal saline, albumin [Alb], or hypertonic saline solution) for 6 to 24 h, followed by echocardiographic and hemodynamic monitoring together with biochemical and histopathologic evaluation. Intervention was to assess the selective influence of load-independent fluid infusion on the aforementioned parameters in groups of animals challenged or not with LPS. At comparative plasma volumes, Alb improved myocardial homeostasis after LPS challenge by (i) reducing left ventricular relative wall diastolic thickness, interstitial space enlargement, and endogenous Alb content; (ii) limiting cardiac apoptosis and sustaining extracellular signal-regulated mitogen-activated protein kinase activation; and (iii) enhancing the expression pattern of heme-oxygenase 1/inducible nitric oxide synthase. Hypertonic saline solution was also cardioprotective by early prevention of myocardial dysfunction and by reducing cardiac apoptosis. Fluid infusions have distinct load-independent structural/biological impacts on endotoxin-induced myocardial dysfunction. Albumin and hypertonic saline solution are the most pleiotropic fluids in protecting the heart after a "sepsis" hit.

Right ventricular pacing with mechanical dyssynchrony causes apoptosis interruptus and calcium mishandling

BACKGROUND

Mechanical dyssynchrony associated with rapid pacing induces cardiac cell stress and myocardial apoptotic pathway activation that has been implicated in the pathophysiology of left ventricular (LV) dysfunction. Effects of dyssynchrony per se are not fully understood. The objective of our study was to test whether ventricular dyssynchrony would elicit myocardial alterations in LV calcium handling regulation and cell survival or apoptosis signalling in right ventricular-paced swine.

METHODS

Implantation of pacemaker was performed under anaesthesia. Endocardial bipolar screw lead was inserted into the right jugular vein and positioned either in the right atrium or at the right ventricular (RV) apex. Swine were paced at 150 beats per minute for 3 weeks.

RESULTS

Compared with right atrial pacing, RV pacing led to abnormal LV sarcoplasmic reticulum calcium uptake (315 ± 65 vs 155 ± 55 nmol/min/mg, P < 0.05) and LV calcium-handling protein expression, ie, 35% reduction in ryanodine receptor 2, 25% decline in sarcoplasmic reticulum Ca(2+) ATPase, 70% increase in Na(+)/Ca(2+) exchanger, and 10% increase in phospholamban. RV pacing also elicited activation of LV apoptotic cascades without nuclear apoptosis. So-called interrupted apoptosis was the result of increased expression of X-linked inhibitor of apoptosis protein. Apoptosis and calcium mishandling were documented in absence of depressed heart function (ejection fraction 62 ± 8% vs 57 ± 12%, in right atrial- and RV-paced hearts, respectively, P > 0.05).

CONCLUSIONS

Slow rate RV pacing causes mechanical dyssynchrony and profound LV alterations in both apoptotic pathways and calcium handling in the early stages of pacing-induced cardiomyopathy.

Cardiac myofilaments: from proteome to pathophysiology

This review addresses the functional consequences of altered post-translational modifications of cardiac myofilament proteins in cardiac diseases such as heart failure and ischemia. The modifications of thick and thin filament proteins as well as titin are addressed. Understanding the functional consequences of altered protein modifications is an essential step in the development of targeted therapies for common cardiac diseases.

Structural changes of the heart during severe sepsis or septic shock

Cardiovascular dysfunction is common in severe sepsis or septic shock. Although functional alterations are often described, the elevated serum levels of cardiac proteins and autopsy findings of myocardial immune cell infiltration, edema, and damaged mitochondria suggest that structural changes to the heart during severe sepsis and septic shock may occur and may contribute to cardiac dysfunction. We explored the available literature on structural (versus functional) cardiac alterations during experimental and human endotoxemia and/or sepsis. Limited data suggest that the structural changes could be prevented, and myocardial function improved by (pre-)treatment with platelet-activating factor, cyclosporin A, glutamine, caffeine, simvastatin, or caspase inhibitors.

Luteolin limits infarct size and improves cardiac function after myocardium ischemia/reperfusion injury in diabetic rats

Background

The present study was to investigate the effects and mechanism of Luteolin on myocardial infarct size, cardiac function and cardiomyocyte apoptosis in diabetic rats with myocardial ischemia/reperfusion (I/R) injury.

Methodology/Principal Findings

Diabetic rats underwent 30 minutes of ischemia followed by 3 h of reperfusion. Animals were pretreated with or without Luteolin before coronary artery ligation. The severity of myocardial I/R induced LDH release, arrhythmia, infarct size, cardiac function impairment, cardiomyocyte apoptosis were compared. Western blot analysis was performed to elucidate the target proteins of Luteolin. The inflammatory cytokine production were also examined in ischemic myocardium underwent I/R injury. Our results revealed that Luteolin administration significantly reduced LDH release, decreased the incidence of arrhythmia, attenuated myocardial infarct size, enhanced left ventricular ejection fraction and decreased myocardial apoptotic death compared with I/R group. Western blot analysis showed that Luteolin treatment up-regulated anti-apoptotic proteins FGFR2 and LIF expression, increased BAD phosphorylation while decreased the ratio of Bax to Bcl-2. Luteolin treatment also inhibited MPO expression and inflammatory cytokine production including IL-6, IL-1a and TNF-a. Moreover, co-administration of wortmannin and Luteolin abolished the beneficial effects of Luteolin.

Conclusions/Significance

This study indicates that Luteolin preserves cardiac function, reduces infarct size and cardiomyocyte apoptotic rate after I/R injury in diabetic rats. Luteolin exerts its action by up-regulating of anti-apoptotic proteins FGFR2 and LIF expression, activating PI3K/Akt pathway while increasing BAD phosphorylation and decreasing ratio of Bax to Bcl-2.

Lipopolysaccharide and sepsis-associated myocardial dysfunction

PURPOSE OF REVIEW

Myocardial dysfunction in sepsis demonstrates acute reduction in left-ventricular function that is potentially reversible yet also associated with increased mortality. The purpose of this review is to discuss the most recent advances in the current knowledge regarding the pathophysiological mechanisms of septic cardiomyopathy.

RECENT FINDINGS

There are numerous candidate pathophysiologic mechanisms for the induction of myocardial dysfunction in sepsis. Sarcolemmal and myofibrillar damage to septic rat cardiomyocytes has been observed, and is likely related to oxidative stress. In a septic chimeric murine model, wild-type mice had decreased cardiac function and increased myocardial TNF-α and IL-6 levels whereas TLR-4 knockout mice had attenuated responses to lipopolysaccharide challenge; thus contributing to the increasing evidence for TLR-4's role in the myocardial inflammatory response to lipopolysaccharide. A similar finding regarding endothelial cell NF-κβ signaling inhibition was found using knockout mice.

SUMMARY

Septic cardiomyopathy is a significant morbid component of severe sepsis and septic shock. Further research into reducing cardiomyocyte damage via oxidative stress, reducing pro-inflammatory responses induced by TLR-4/NF-κβ signaling, decreasing mitochondrial dysfunction, and improving cellular respiration thereby decreasing apoptosis are examples of areas that may be future therapeutic targets.

Age exacerbates chronic catecholamine-induced impairments in contractile reserve in the rat

Contractile reserve decreases with advancing age and chronic isoproterenol (ISO) administration is a well-characterized model of cardiac hypertrophy known to impair cardiovascular function. This study evaluated whether nonsenescent, mature adult rats are more susceptible to detrimental effects of chronic ISO administration than younger adult rats. Rats received daily injections of ISO (0.1 mg/kg sc) or vehicle for 3 wk. ISO induced a greater impairment in contractile reserve [maximum of left ventricular pressure development (Δ+dP/dt(max))] in mature adult ISO-treated (MA-ISO) than in young adult ISO-treated rats (YA-ISO) in response to infusions of mechanistically distinct inotropes (digoxin, milrinone; 20-200 μl·kg(-1)·min(-1)), while basal and agonist-induced changes in heart rate and systolic arterial pressure (SAP) were not different across groups. ISO decreased expression of the calcium handling protein, sarco(endo)plasmic reticulum Ca(2+)-ATPase-2a, in MA-ISO compared with YA, YA-ISO, and MA rats. Chronic ISO also induced greater increases in cardiac hypertrophy [left ventricular (LV) index: 33 ± 3 vs. 22 ± 5%] and caspase-3 activity (34 vs. 5%) in MA-ISO relative to YA-ISO rats. Moreover, β-myosin heavy chain (β-MHC) and atrial natriuretic factor (ANF) mRNA expression was significantly elevated in MA-ISO. These results demonstrate that adult rats develop greater impairments in systolic performance than younger rats when exposed to chronic catecholamine excess. Reduced contractile reserve may result from calcium dysregulation, increased caspase-3 activity, or increased β-MHC and ANF expression. Although several studies report age-related declines in systolic performance in older and senescent animals, the present study demonstrates that catecholamine excess induces reductions in systolic performance significantly earlier in life.

MCP-1-induced protein attenuates endotoxin-induced myocardial dysfunction by suppressing cardiac NF-кB activation via inhibition of IкB kinase activation

Myocardial contractile dysfunction is a major consequence of septic shock, which is mainly mediated by nuclear factor-kappa B (NF-кB)-dependent production of inflammatory mediators in the heart. A novel zinc-finger protein, MCP-1-induced protein (MCPIP), is thought to have NF-кB inhibitory activity in certain cell cultures, but its pathophysiological consequence in vivo remains undefined. This study aims to clarify whether the anti-inflammatory potency of MCPIP contribute to amelioration of septic myocardial inflammation and dysfunction in vivo. Transgenic mice (TG) with cardiac-specific expression of MCPIP and their littermate wild-type (WT) controls were challenged with Escherichia coli LPS (10mg/kg ip) and myocardial function was assessed 18 h later using echocardiography. LPS administration markedly deteriorated myocardial contractile function evidenced by reduction of the percentage of left ventricular fractional shortening, which was significantly attenuated by myocardial expression of MCPIP. MCPIP TG mice exhibited a markedly reduced myocardial inflammatory cytokines, less of iNOS expression and peroxynitrite formation, decreased caspase-3/7 activities and apoptotic cell death compared with LPS-treated WT mice. Activation of cardiac NF-кB observed in LPS-challenged WT mice was suppressed by the presence of MCPIP, as evidenced by decreased phosphorylation of IкB kinase (IKKα/β), reduced degradation of the cytosolic IкBα, and decreased nuclear translocation of NF-кB p65 subunit and its target DNA-binding activity. These results suggest that MCPIP has therapeutic values to protect heart from inflammatory pathologies, possibly through inhibition of IкB kinase complex, leading to blockade of NF-кB activation, and subsequently, attenuation of the proinflammatory state and nitrosative stress in the myocardium.