Increased cardiomyocyte intracellular calcium during endotoxin-induced cardiac dysfunction in guinea pigs

Activation of STIM1/Orai1‑mediated SOCE in sepsis‑induced myocardial depression

Unbalanced Ca2⁺ homeostasis serves an essential role in the occurrence and development of septic myocardial injury. However, the mechanism of Ca2⁺ homeostasis in septic myocardial depression is poorly understood due to the complexity of Ca2⁺ transporters in excitable cells. It was therefore hypothesized that cardiac dysfunction, myocardial injury and cardiac apoptosis in septic myocardial depression are associated with elevated intracellular Ca2⁺ concentrations caused by stromal interaction molecule 1 (STIM1)/Orai calcium release‑activated calcium modulator 1 (Orai1)‑mediated store‑operated Ca2⁺ entry (SOCE). A septic myocardial depression model was established using the cecal ligation and puncture operation (CLP) in mice and was simulated in H9C2 cells via lipopolysaccharide (LPS) stimulation. Cardiac function, myocardial injury, cardiac apoptosis and the expression levels of Bax, Bcl‑2, STIM1 and Orai1 were quantified in vivo at 6, 12 and 24 h. Changes in the intracellular Ca2⁺ concentration, SOCE and the distribution of STIM1 were assessed in vitro within 6 h. The morphological changes of heart tissue were observed by hematoxylin‑eosin staining. Myocardial cellular apoptosis was determined by TUNEL method. The expression of Bax, Bcl‑2, STIM1 and Orai1 were visualized by western blot. Cytosolic calcium concentration and SOCE were evaluated by confocal microscopy. The results demonstrated that cardiac contractile function was significantly reduced at 6 h and morphological changes in cardiac tissues, as well as the myocardial apoptosis rate, were markedly increased at 6, 12 and 24 h following CLP. mRNA and protein expression levels of Bax/Bcl‑2 were significantly enhanced at 6 and 12 h and glycosylation of Orai1 in the myocardium of septic mice was significantly increased at 6 h following CLP. The intracellular Ca2⁺ concentration, SOCE, was significantly increased at 1‑2 h and the clustering and distribution of STIM1 were markedly changed in H9C2 cells at 1 and 2 h. These findings suggested that myocardial dysfunction, cardiac injury and myocardial depression may be related to increased intracellular Ca2⁺ concentration resulting from STIM1/Orai1‑mediated SOCE, which may provide a potential method to alleviate septic myocardial depression.

Biological active ingredients of Astragali Radix and its mechanisms in treating cardiovascular and cerebrovascular diseases

BACKGROUND

With the rising age of the global population, the incidence rate of cardiovascular and cerebrovascular diseases (CCVDs) is increasing, which causes serious public health burden. The efforts for new therapeutic approaches are still being sought since the treatment effects of existing therapies are not quite satisfactory. Chinese traditional medicine proved to be very efficient in the treatment of CCVDs. Well described and established in Chinese medicine, Astragali Radix, has been commonly administered in the prophylaxis and cure of CCVDs for thousands of years.

PURPOSE

This review summarized the action mode and mechanisms of Astragali Radix phytochemicals on CCVDs, hoping to provide valuable information for the future application, development and improvement of Astragali Radix as well as CCVDs treatment.

METHODS

A plenty of literature on biological active ingredients of Astragali Radix used for CCVDs treatment were retrieved from online electronic PubMed and Web of Science databases.

RESULTS

This review highlighted the effects of five main active components in Astragali Radix including astragaloside Ⅳ, cycloastragenol, astragalus polysaccharide, calycosin-7-O-β-d-glucoside, and calycosin on CCVDs. The mechanisms mainly involved anti-oxidative damage, anti-inflammatory, and antiapoptotic through signaling pathways such as PI3K/Akt, Nrf2/HO-1, and TLR4/NF-κB pathway. In addition, the majority active constituents in AR have no obvious toxic side effects.

CONCLUSION

The main active components of Astragali Radix, especially AS-IV, have been extensively summarized. It has been proved that Astragali Radix has obvious therapeutic effects on various CCVDs, including myocardial and cerebral ischemia, hypertension, atherosclerosis, cardiac hypertrophy, chronic heart failure. CAG possesses anti-ischemia activity without toxicity, indicating a worthy of further development. However, high-quality clinical and pharmacokinetic studies are required to validate the current studies.

Wnt/β-Catenin Antagonist Pyrvinium Exerts Cardioprotective Effects in Polymicrobial Sepsis Model by Attenuating Calcium Dyshomeostasis and Mitochondrial Dysfunction

Calcium dysregulation and mitochondrial dysfunction are key elements in the development of sepsis-induced cardiac dysfunction. Evidences have suggested that inhibition of Wnt/β-Catenin signalling prevents cardiac dysfunction and remodelling in surgical, hypertension and pressure overload models. The present study investigated the effects of Wnt/β-Catenin inhibitor on calcium overload and mitochondrial dysfunction in rat sepsis model of cardiomyopathy. Induction of sepsis by cecal ligation puncture (CLP) resulted in the up-regulation of cardiac β-catenin transcriptional levels and cardiac dysfunction depicted by increased serum lactate dehydrogenase, CK-MB levels reduced maximum (dp/dt max.) and minimum developed pressure (dp/dt min.), increased LVEsDP and relaxation constant tau values. Moreover, oxidative and inflammatory stress, immune cell infiltration, increased myeloperoxidase activity, enhanced caspase-3 activity and fibronectin protein levels were observed in septic rat's heart. Also, septic rat's heart displayed mitochondrial dysfunction due to mPTP opening, increased calcium up-regulation in left ventricular apex tissues and whole heart, increased collagen staining, necrosis and structural damage. Pre-treatment with Wnt/β-Catenin antagonist attenuated sepsis-induced serum and tissue biochemical changes, cardiac dysfunction and structural alterations by inhibiting mitochondrial mPTP opening and restricting calcium overloading in cardiac tissue.

COVID-19 and Toll-Like Receptor 4 (TLR4): SARS-CoV-2 May Bind and Activate TLR4 to Increase ACE2 Expression, Facilitating Entry and Causing Hyperinflammation

Causes of mortality from COVID-19 include respiratory failure, heart failure, and sepsis/multiorgan failure. TLR4 is an innate immune receptor on the cell surface that recognizes pathogen-associated molecular patterns (PAMPs) including viral proteins and triggers the production of type I interferons and proinflammatory cytokines to combat infection. It is expressed on both immune cells and tissue-resident cells. ACE2, the reported entry receptor for SARS-CoV-2, is only present on ~1-2% of the cells in the lungs or has a low pulmonary expression, and recently, the spike protein has been proposed to have the strongest protein-protein interaction with TLR4. Here, we review and connect evidence for SARS-CoV-1 and SARS-CoV-2 having direct and indirect binding to TLR4, together with other viral precedents, which when combined shed light on the COVID-19 pathophysiological puzzle. We propose a model in which the SARS-CoV-2 spike glycoprotein binds TLR4 and activates TLR4 signalling to increase cell surface expression of ACE2 facilitating entry. SARS-CoV-2 also destroys the type II alveolar cells that secrete pulmonary surfactants, which normally decrease the air/tissue surface tension and block TLR4 in the lungs thus promoting ARDS and inflammation. Furthermore, SARS-CoV-2-induced myocarditis and multiple-organ injury may be due to TLR4 activation, aberrant TLR4 signalling, and hyperinflammation in COVID-19 patients. Therefore, TLR4 contributes significantly to the pathogenesis of SARS-CoV-2, and its overactivation causes a prolonged or excessive innate immune response. TLR4 appears to be a promising therapeutic target in COVID-19, and since TLR4 antagonists have been previously trialled in sepsis and in other antiviral contexts, we propose the clinical trial testing of TLR4 antagonists in the treatment of severe COVID-19. Also, ongoing clinical trials of pulmonary surfactants in COVID-19 hold promise since they also block TLR4.

A novel role of nifuroxazide in attenuation of sepsis-associated acute lung and myocardial injuries; role of TLR4/NLPR3/IL-1β signaling interruption

Acute lung injury (ALI) and the subsequent multi-system organ failure is a serious health problem with devastating impacts on the health care systems. Indeed, the world has been facing an un-preceded situation in the past couple of months following COVID-19 infestation and the associated high-mortality rates mainly attributed to sepsis and the associated multiple organ failures of particular concern; acute respiratory distress syndrome post lung injury. The current study provides evidence on the ameliorative impact of nifuroxazide, and FDA approved antidiarrheal drug in attenuation of lipopolysaccharide (LPS)-induced ALI and myocarditis when administrated either in prophylactic or curative regimens. Nifuroxazide administration was associated with a significant improvement in lung and heart histopathological characteristics and architecture with retraction of LPS-induced inflammatory-infiltration. This was associated with retraction in serum biomarkers of cellular injury of which; LDH, CK-MB, and ALP. Nifuroxazide administration was associated with a significant improvement in both lung and heart oxidative status. Such positive outcomes were underlined by a significant inhibitory effect of nifuroxazide on lung and heart contents of toll-like receptor (4) (TLR4)/the inflammasome NALPR3/interleukin- 1β (IL-1β). In conclusion: Nifuroxazide attenuates LPS-induced ALI and myocardial injury via interruption of TLR4/NALPR3/IL-1β signaling. Thus it can offer a potential approach for attenuation of sepsis in critically ill patients.

Maternal obesity impairs fetal cardiomyocyte contractile function in sheep

Obesity is a major public health problem worldwide. In the United States, one-third of women of reproductive age are obese. Human studies show that maternal obesity (MO) predisposes offspring to cardiovascular disease. However, the underlying mechanisms remain unclear. Given the similarities between pregnancy in sheep and humans, we studied sheep to examine the impact of MO on fetal cardiomyocyte contractility at term. We observed that MO impaired cardiomyocyte contractility by reducing peak shortening and shortening/relengthening velocity, prolonging time to relengthening. MO disrupted Ca²⁺ homeostasis in fetal cardiomyocytes, increasing intracellular Ca²⁺ and inducing cellular Ca²⁺ insensitivity. The Ca²⁺-release channel was impaired, but Ca²⁺ uptake was unaffected by MO. The upstream kinases that phosphorylate the Ca²⁺-release channel-ryanodine receptor-2, PKA, and calmodulin-dependent protein kinase II-were activated in MO fetuses. Contractile dysfunction was associated with an increased ratio of myosin heavy chain (MHC)-β to MHC-α and upregulated cardiac troponin (cTn)-T and tropomyosin, as well as cTn-I phosphorylation. In summary, this is the first characterization of the effects of MO on fetal cardiomyocyte contractility. Our findings indicate that MO impairs fetal cardiomyocyte contractility through altered intracellular Ca²⁺ handling, overloading fetal cardiomyocyte intracellular Ca²⁺ and aberrant myofilament protein composition. These mechanisms may contribute to developmental programming by MO of offspring cardiac function and predisposition to later life cardiovascular disease in the offspring.-Wang, Q., Zhu, C., Sun, M., Maimaiti, R., Ford, S. P., Nathanielsz, P. W., Ren, J., Guo, W. Maternal obesity impairs fetal cardiomyocyte contractile function in sheep.

The immune system's role in sepsis progression, resolution, and long-term outcome

Sepsis occurs when an infection exceeds local tissue containment and induces a series of dysregulated physiologic responses that result in organ dysfunction. A subset of patients with sepsis progress to septic shock, defined by profound circulatory, cellular, and metabolic abnormalities, and associated with a greater mortality. Historically, sepsis-induced organ dysfunction and lethality were attributed to the complex interplay between the initial inflammatory and later anti-inflammatory responses. With advances in intensive care medicine and goal-directed interventions, early 30-day sepsis mortality has diminished, only to steadily escalate long after "recovery" from acute events. As so many sepsis survivors succumb later to persistent, recurrent, nosocomial, and secondary infections, many investigators have turned their attention to the long-term sepsis-induced alterations in cellular immune function. Sepsis clearly alters the innate and adaptive immune responses for sustained periods of time after clinical recovery, with immune suppression, chronic inflammation, and persistence of bacterial representing such alterations. Understanding that sepsis-associated immune cell defects correlate with long-term mortality, more investigations have centered on the potential for immune modulatory therapy to improve long-term patient outcomes. These efforts are focused on more clearly defining and effectively reversing the persistent immune cell dysfunction associated with long-term sepsis mortality.

Endotoxin Effects on Cardiac and Renal Functions and Cardiorenal Syndromes

Gram-negative sepsis is a major cause of morbidity and mortality in critical ill patients. Recent findings in molecular biology and in signaling pathways have enhanced our understanding of its pathogenesis and opened up opportunities of innovative therapeutic approaches. Endotoxin plays a pivotal role in the pathogenesis of multi-organ dysfunction in the setting of gram-negative sepsis. Indeed, heart and kidney impairments seem to be induced by the release of circulating pro-inflammatory and pro-apoptotic mediators triggered by endotoxin interaction with immune cells. These molecules are responsible for cellular apoptosis, autophagy, cell cycle arrest, and microRNAs activation. Therefore, the early identification of sepsis-associated acute kidney injury and heart dysfunction may improve the patient clinical outcome. In this report, we will consider the role of endotoxin in the pathogenesis of sepsis, its effects on both cardiac and renal functions, and the interactions between these 2 systems in the setting of cardiorenal syndromes (CRS), particularly in CRS type 5. Finally, we will discuss the possible role of extracorporeal therapies in reducing endotoxin levels.

The effect of Nigella sativa on inflammation-induced myocardial fibrosis in male rats

Nigella sativa (NS) (Ranunculaceae) used as a protective and therapeutic traditional medicine. This study evaluates the effect of NS on inflammation-induced myocardial fibrosis, serum and tissue inflammatory markers, and oxidative stress status in male rats. Fifty male Wistar rats were divided into five groups: (1) control; (2) lipopolysaccharide (LPS), 1 mg/kg/day; (3) LPS + NS (hydroalcoholic extract), 100 mg/kg/day; (4) LPS + NS, 200 mg/kg/day; (5) LPS + NS, 400 mg/kg/day (n = 10 in each group). The duration of LPS administration was two weeks. At the end of the experiment, blood samples were taken and ventricles were homogenized and stained for histological evaluation. Serum nitrite levels were lower in LPS group than the control group (22.98 ± 1.03 vs 28.5 ± 0.93 μmol/L), in which they were significantly increased by NS treatment (P < 0.05). Higher levels of heart interlukine-6 (IL-6) and tumor necrosis factor-α (TNF-α) were observed in LPS group compared to the controls (IL-6: 6805 ± 656 vs 4733 ± 691 pg/mL; TNF-α: 6504 ± 501 vs 5309 ± 452 pg/mL), in which they were reduced by NS 400 mg/kg compared to LPS groups (P < 0.05). A significant increment of malondialdehyde and reduction in heart total thiol, superoxide dismutase and catalase concentrations were observed in LPS group (p < 0.05) which significantly restored with treatment by three doses of NS. Histopathological studies showed higher inflammatory cell infiltrates, cardiac fibrosis, and collagen deposition in LPS group, which were reduced by the administration of NS. Treatment by NS reduced myocardial fibrosis in inflammation-induced fibrosis, possibly through improving oxidative/anti-oxidative balance.

The Sick and the Weak: Neuropathies/Myopathies in the Critically Ill

Critical illness polyneuropathies (CIP) and myopathies (CIM) are common complications of critical illness. Several weakness syndromes are summarized under the term intensive care unit-acquired weakness (ICUAW). We propose a classification of different ICUAW forms (CIM, CIP, sepsis-induced, steroid-denervation myopathy) and pathophysiological mechanisms from clinical and animal model data. Triggers include sepsis, mechanical ventilation, muscle unloading, steroid treatment, or denervation. Some ICUAW forms require stringent diagnostic features; CIM is marked by membrane hypoexcitability, severe atrophy, preferential myosin loss, ultrastructural alterations, and inadequate autophagy activation while myopathies in pure sepsis do not reproduce marked myosin loss. Reduced membrane excitability results from depolarization and ion channel dysfunction. Mitochondrial dysfunction contributes to energy-dependent processes. Ubiquitin proteasome and calpain activation trigger muscle proteolysis and atrophy while protein synthesis is impaired. Myosin loss is more pronounced than actin loss in CIM. Protein quality control is altered by inadequate autophagy. Ca(2+) dysregulation is present through altered Ca(2+) homeostasis. We highlight clinical hallmarks, trigger factors, and potential mechanisms from human studies and animal models that allow separation of risk factors that may trigger distinct mechanisms contributing to weakness. During critical illness, altered inflammatory (cytokines) and metabolic pathways deteriorate muscle function. ICUAW prevention/treatment is limited, e.g., tight glycemic control, delaying nutrition, and early mobilization. Future challenges include identification of primary/secondary events during the time course of critical illness, the interplay between membrane excitability, bioenergetic failure and differential proteolysis, and finding new therapeutic targets by help of tailored animal models.

Calcium supplementation during sepsis exacerbates organ failure and mortality via calcium/calmodulin-dependent protein kinase kinase signaling

BACKGROUND

Calcium plays an essential role in nearly all cellular processes. As such, cellular and systemic calcium concentrations are tightly regulated. During sepsis, derangements in such tight regulation frequently occur, and treating hypocalcemia with parenteral calcium administration remains the current practice guideline.

OBJECTIVE

We investigated whether calcium administration worsens mortality and organ dysfunction using an experimental murine model of sepsis and explored the mechanistic role of the family of calcium/calmodulin-dependent protein kinases in mediating these physiological effects. To highlight the biological relevance of these observations, we conducted a translational study of the association between calcium administration, organ dysfunction, and mortality among a cohort of critically ill septic ICU patients.

DESIGN

Prospective, randomized controlled experimental murine study and observational clinical cohort analysis.

SETTING

University research laboratory and eight ICUs at a tertiary care center.

PATIENTS

A cohort of 870 septic ICU patients.

SUBJECTS

C57Bl/6 and CaMKK mice.

INTERVENTIONS

Mice underwent cecal ligation and puncture polymicrobial sepsis and were administered with calcium chloride (0.25 or 0.25 mg/kg) or normal saline.

MEASUREMENTS AND MAIN RESULTS

Administering calcium chloride to septic C57Bl/6 mice heightened systemic inflammation and vascular leak, exacerbated hepatic and renal dysfunction, and increased mortality. These events were significantly attenuated in CaMKK mice. In a risk-adjusted analysis of septic patients, calcium administration was associated with an increased risk of death, odds ratio 1.92 (95% CI, 1.00-3.68; p = 0.049), a significant increase in the risk of renal dysfunction, odds ratio 4.74 (95% CI, 2.48-9.08; p < 0.001), and a significant reduction in ventilator-free days, mean decrease 3.29 days (0.50-6.08 days; p = 0.02).

CONCLUSIONS

Derangements in calcium homeostasis occur during sepsis that is sensitive to calcium administration. This altered calcium signaling, transduced by the calmodulin-dependent protein kinase kinase cascade, mediates heightened inflammation and vascular leak that culminates in elevated organ dysfunction and mortality. In the clinical management of septic patients, calcium supplementation provides no benefit and may impose harm.

HDL Mimetic Peptide Administration Improves Left Ventricular Filling and Cardiac output in Lipopolysaccharide-Treated Rats

AIMS: Cardiac dysfunction is a complication of sepsis and contributes to morbidity and mortality. Since raising plasma apolipoprotein (apo) A-I and high density lipoprotein (HDL) concentration reduces sepsis complications, we tested the hypothesis that the apoA-I mimetic peptide 4F confers similar protective effects in rats treated with lipopolysaccharide (LPS). METHODS AND RESULTS: Male Sprague-Dawley (SD) rats were randomized to receive saline vehicle (n=13), LPS (10 mg/kg: n=16) or LPS plus 4F (10 mg/kg each: n=13) by intraperitoneal injection. Plasma cytokine and chemokine levels were significantly elevated 24 hrs after LPS administration. Echocardiographic studies revealed changes in cardiac dimensions that resulted in a reduction in left ventricular end-diastolic volume (LVEDV), stroke volume (SV) and cardiac output (CO) 24 hrs after LPS administration. 4F treatment reduced plasma levels of inflammatory mediators and increased LV filling, resulting in improved cardiac performance. Chromatographic separation of lipoproteins from plasma of vehicle, LPS and LPS+4F rats revealed similar profiles. Further analyses showed that LPS treatment reduced the agarose electrophoretic mobility of isolated HDL fractions. HDL-associated proteins were characterized by SDSPAGE and mass spectrometry. ApoA-I and apoA-IV were reduced while apoE content was increased in LPStreated rats. 4F treatment in vivo attenuated changes in HDL-associated apolipoproteins and increased the electrophoretic mobility of the particle. CONCLUSIONS: The ability of 4F to reduce inflammation and improve cardiac performance in LPS-treated rats may be due to its capacity to neutralize endotoxin and prevent adverse changes in HDL composition and function.

Toll-like receptor 4 stimulation initiates an inflammatory response that decreases cardiomyocyte contractility

Toll-like receptors (TLRs) have been identified as primary innate immune receptors for the recognition of pathogen-associated molecular patterns by immune cells, initiating a primary response toward invading pathogens and recruitment of the adaptive immune response. TLRs, especially Toll-like receptor 4 (TLR4), can also be stimulated by host-derived molecules and are expressed in the cardiovascular system, thus acting as a possible key link between cardiovascular diseases and the immune system. TLR4 is involved in the acute myocardial dysfunction caused by septic shock and myocardial ischemia. We used wild-type (WT) mice, TLR4-deficient (TLR4-knockout [ko]) mice, and chimeras that underwent myeloablative bone marrow transplantation to dissociate between TLR4 expression in the heart (TLR4-ko/WT) and the immunohematopoietic system (WT/TLR4-ko). Following lipopolysaccharide (LPS) challenge (septic shock model) or coronary artery ligation, myocardial ischemia (MI) model, we found WT/TLR4-ko mice challenged with LPS or MI displayed reduced cardiac function, increased myocardial levels of interleukin-1β and tumor necrosis factor-α, and upregulation of mRNA encoding TLR4 prior to myocardial leukocyte infiltration. The cardiac function of TLR4-ko or WT/TLR4-ko mice was less affected by LPS and demonstrated reduced suppression by MI compared with WT. These results suggest that TLR4 expressed in the cardiomyocytes plays a key role in this acute phenomenon.

Cross-bridge apparent rate constants of human gallbladder smooth muscle

This paper studies human gallbladder (GB) smooth muscle contractions. A two-state cross-bridge model was used to estimate the apparent attachment and detachment rate constants, as well as increased Ca2+ concentration from the peak active stress during the isometric contraction. The active stress was computed from a mechanical model based entirely on non-invasive routine ultrasound scans. In the two-state cross-bridge model, the two apparent rate constants, representing the total attached/detached cross-bridges, respectively, were estimated using active stress prediction for 51 subjects undergoing cholecystokinin-provocation test, together with estimates from the four-state cross-bridge model for a swine carotid, bovine tracheal and guinea pig GB smooth muscles. The study suggests that the apparent rate constants should be patient-specific, i.e. patients with a lower stress level are characterized by smaller apparent rate constants. In other words, the diseased GB may need to develop fast cycling cross-bridges to compensate in the emptying process. This is a first step towards more quantitative and non-invasive measures of GB pain, and may provide useful insight in understanding GB motility and developing effective drug treatments.

Complement dependency of cardiomyocyte release of mediators during sepsis

We have recently shown that antibody-induced blockade of C5a, C5a receptors, or IL-17A greatly reduced the harmful outcomes of sepsis. In the current study, normal cardiomyocytes from young (300 g) male Sprague-Dawley rats responded in vitro to C5a (ED(50)=55 nM) with release of IL-6 and TNFα, peaking between 2 to 8 h. Neutralizing antibodies to mouse C5a or IL-17A (ED(50)=40 μg for each, based on improved survival) reduced spontaneous in vitro release of cardiosuppressive cytokines and chemokines in cardiomyocytes obtained from mice with polymicrobial sepsis. A non-neutralizing C5a antibody had no such effects. Cardiomyocytes from septic mice (C57Bl/6) showed increased mRNA for TNFR1, IL-6 (gp80), and C5aR at 6 h after sepsis. Cardiomyocytes from septic C5aR(-/-) or C5L2(-/-) mice did not show spontaneous in vitro release of cytokines and chemokines. These data suggest that cardiomyocytes from septic mice release suppressive cytokines in a C5a-, C5aR-, and IL-17A-dependent manner, followed by mediator reactivity with receptors on cardiomyocytes, resulting in defective contractility and relaxation. These data may be relevant to a strategy for the treatment of heart dysfunction developing during sepsis.

Cardiomyocyte Toll-like receptor 4 is involved in heart dysfunction following septic shock or myocardial ischemia

Toll-like receptors are expressed in immune cells and cardiac muscle. We examined whether the cardiac Toll-like receptor 4 (TLR4) is involved in the acute myocardial dysfunction caused by septic shock and myocardial ischemia (MI). We used wild type mice (WT), TLR4 deficient (TLR4-ko) mice and chimeras that underwent myeloablative bone marrow transplantation to dissociate between TLR4 expression in the heart (TLR4-ko/WT) and the immunohematopoietic system (WT/TLR4-ko). Mice were injected with lipopolysaccharide (LPS) (septic shock model) or subjected to coronary artery ligation (MI model) and tested in vivo and ex vivo, for function, histopathology proinflammatory cytokine and TLR4 expression. WT mice challenged with LPS or MI displayed reduced cardiac function, increased myocardial levels of IL-1 beta and TNF-alpha and upregulation of mRNA encoding TLR4 prior to myocardial leukocyte infiltration. TLR4 deficient mice sustained significantly smaller infarctions as compared to control mice at comparable areas at risk. The cardiac function of TLR4-ko mice was not affected by LPS and demonstrated reduced suppression by MI compared to WT. Chimeras deficient in myocardial TLR4 were resistant to suppression induced by LPS and the heart function was less depressed, compared to the TLR4-ko, following MI in the acute phase (4h). In contrast, hearts of chimeras deficient in immunohematopoietic TLR4 expression were suppressed both by LPS and MI, exhibiting increased myocardial cytokine levels, similar to WT mice. We concluded that cardiac function of TLR4-ko mice and chimeric mice expressing TLR4 in the immunohematopoietic system, but not in the heart, revealed resistance to LPS and reduced cardiac depression following MI, suggesting that TLR4 expressed by the cardiomyocytes themselves plays a key role in this acute phenomenon.

Parenteral calcium for intensive care unit patients

BACKGROUND

Hypocalcemia is prevalent among critically ill patients requiring intensive care. Several epidemiological studies highlight a direct association between hypocalcemia and mortality. These data provide the impetus for current guidelines recommending parenteral calcium administration to normalize serum calcium. However, in light of the considerable variation in the threshold for calcium replacement, the lack of evidence to support a causal role of hypocalcemia in mortality, and animal studies illustrating that calcium supplementation may worsen outcomes, a systematic review is essential to evaluate whether or not the practice of calcium supplementation for intensive care unit (ICU) patients provides any benefit.

OBJECTIVES

To assess the effects of parenteral calcium administration in ICU patients on the following outcomes: mortality, multiple organ dysfunction, ICU and hospital length of stay, costs, serum ionized calcium concentration, and complications of parenteral calcium administration.

SEARCH STRATEGY

We searched The Cochrane Library, MEDLINE, EMBASE, Current Controlled Trials, and the National Research Register. We hand-searched conference abstracts from the Society of Critical Care Medicine, the European Society of Intensive Care Medicine, the American Thoracic Surgery, the American College of Surgeons, the American College of Chest Physicians, the American College of Physicians, and the International Consensus Conference in Intensive Care Medicine. We checked references of publications and attempted to contact authors to identify additional published or unpublished data.

SELECTION CRITERIA

Randomised controlled and controlled clinical trials of ICU patients comparing parenteral calcium chloride or calcium gluconate administration with no treatment or placebo.

DATA COLLECTION AND ANALYSIS

Two reviewers independently applied eligibility criteria to trial reports for inclusion and extracted data.

MAIN RESULTS

There are no identifiable studies that have evaluated the association between parenteral calcium supplementation in critically ill ICU patients and the following outcomes: mortality, multiple organ dysfunction, ICU and hospital length of stay, costs, and complications of calcium administration. Serum ionized calcium concentration was reported in 5 studies (12 trial arms, 159 participants). These trials showed a small but significant increase in serum ionized calcium concentration after calcium administration. These trials showed considerable statistical heterogeneity and differed extensively in the population studied (adult versus neonate), the indication (hypocalcemia versus prophylaxis) and threshold of hypocalcemia for which parenteral calcium was administered, and the timing of subsequent measurement of serum ionized calcium concentration to the extent that we consider a pooled estimate almost inappropriate.

AUTHORS' CONCLUSIONS

There is no clear evidence that parenteral calcium supplementation impacts the outcome of critically ill patients.

Prevention of endotoxin-induced sarcoplasmic reticulum calcium leak improves mitochondrial and myocardial dysfunction

OBJECTIVE

Growing evidence suggests that mitochondria function is impaired in sepsis. Here, we tested the hypothesis that lipopolysaccharide would induce mitochondrial Ca2+ overload and oxygen utilization abnormalities as consequences of sarcoplasmic reticulum Ca2+ handling derangements that are typically observed in sepsis. As lipopolysaccharide-induced sarcoplasmic reticulum dysfunction was mainly characterized by reduced sarcoplasmic reticulum Ca2+ uptake and Ca2+ leak, we tested whether dantrolene, a sarco(endo)plasmic reticulum calcium ATPase leak inhibitor, would prevent mitochondrial and cardiac contractile dysfunction.

DESIGN

Randomized controlled trial.

SETTING

Experimental laboratory.

SUBJECTS

Male Sprague Dawley rats.

INTERVENTIONS

Sepsis was induced by injection of endotoxin lipopolysaccharide (10 mg/kg/intravenously). Assessment of contractile function and Ca2+ handling was performed 4 hr after lipopolysaccharide. The relative contribution of the different Ca2+ transporters to relaxation in intact cardiomyocytes was studied during successive electrically evoked twitches and caffeine stimulation. Sarcoplasmic reticulum vesicles and mitochondria from ventricles of rats treated or not with lipopolysaccharide were prepared to evaluate Ca2+ uptake-release and oxygen fluxes, respectively. Effects of dantrolene (10 mg/kg) treatment in rats were evaluated in sarcoplasmic reticulum vesicles, mitochondria, and isolated hearts.

MEASUREMENTS AND MAIN RESULTS

Lipopolysaccharide challenge elicited cardiac contractile dysfunction that was accompanied by severe derangements in sarcoplasmic reticulum function, i.e., reduced Ca2+ uptake and increased sarcoplasmic reticulum Ca2+ leak. Functional sarcoplasmic reticulum changes were associated with modification in the status of phospholamban phosphorylation whereas SERCA was unchanged. Rises in mitochondrial Ca2+ content observed in lipopolysaccharide-treated rats coincided with derangements in mitochondrial oxygen efficacy, i.e., reduced respiratory control ratio. Administration of dantrolene in lipopolysaccharide-treated rats prevented mitochondrial Ca2+ overload and mitochondrial oxygen utilization abnormalities. Moreover, dantrolene treatment in lipopolysaccharide rats improved heart mitochondrial redox state and myocardial dysfunction.

CONCLUSION

These experiments suggest that sarcoplasmic reticulum Ca2+ handling dysfunction is an early event during endotoxemia that could be responsible for, or contribute to, mitochondrial Ca2+ overload, metabolic failure, and cardiac dysfunction.

Cardiac Pharmacokinetics and Inotropic Response of Verapamil in Rats With Endotoxemia

The present study evaluated the effect of endotoxin-induced systemic inflammation on cardiac uptake and negative inotropic response to verapamil in isolated rat hearts. Rats received an i.p. dose of 4 mg/kg Escherichia coli lipopolysaccharide (LPS) or saline. After 5.5 h the outflow concentration-time curve and inotropic response data were measured following a 1.5 nmol dose of [(3)H]-verapamil (infused within 1 min) in Langendorff-perfused hearts and analyzed by pharmacokinetic/pharmacodynamic modeling, where the inotropic effects at individual time points were evaluated in relation to outflow concentrations at corresponding times. Endotoxemia decreased the rate of cardiac verapamil uptake and the maximal negative inotropic effect E(max) to 78% and 55%, respectively, of the values estimated in the control group (p < 0.01). The reduction in E(max) was correlated with the increase in body temperature. With verapamil as a model drug, the results give some information about potential effects of endotoxemia on the cardiac kinetics and dynamics of calcium antagonists.

Lipopolysaccharide induces cellular hypertrophy through calcineurin/NFAT-3 signaling pathway in H9c2 myocardiac cells

Evidences suggest that lipopolysaccharide (LPS) participates in the inflammatory response in the cardiovascular system; however, it is unknown if LPS is sufficient to cause the cardiac hypertrophy. In the present study, we treated H9c2 myocardiac cells with LPS to explore whether LPS causes cardiac hypertrophy, and to identify the precise molecular and cellular mechanisms behind hypertrophic responses. Here we show that LPS challenge induces pathological hypertrophic responses such as the increase in cell size, the reorganization of actin filaments, and the upregulation of hypertrophy markers including atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) in H9c2 cells. LPS treatment significantly promotes the activation of GATA-4 and the nuclear translocation of NFAT-3, which act as transcription factors mediating the development of cardiac hypertrophy. After administration of inhibitors including U0126 (ERK1/2 inhibitor), SB203580 (p38 MAPK inhibitor), SP600125 (JNK1/2 inhibitor), CsA (calcineurin inhibitor), FK506 (calcineurin inhibitor), and QNZ (NFkappaB inhibitor), LPS-induced hypertrophic characteristic features, such as increases in cell size, actin fibers, and levels of ANP and BNP, and the nuclear localization of NFAT-3 are markedly inhibited only by calcineurin inhibitors, CsA and FK506. Collectively, these results suggest that LPS leads to myocardiac hypertrophy through calcineurin/NFAT-3 signaling pathway in H9c2 cells. Our findings further provide a link between the LPS-induced inflammatory response and the calcineurin/NFAT-3 signaling pathway that mediates the development of cardiac hypertrophy.

Sepsis and burn complicated by sepsis alter cardiac transporter expression

Sepsis alone and burn complicated by sepsis produce significant cardiac dysfunction. Since calcium handling by the cardiomyocyte is essential for cardiac function, one mechanism for cardiac abnormalities may be calcium dyshomeostasis. We hypothesized that sepsis and burn plus sepsis alter cardiac calcium transporter expression. Sprague-Dawley rats were divided into: (1) control, (2) sepsis (intratracheal S. Pneumoniae, 4x10(6) CFU), and (3) burn (40% TBSA) plus sepsis. Myocyte [Ca(2+)](i) and [Na(+)](i) were quantified with Fura-2 AM and SBFI, respectively. Western blot analysis of rat hearts used antibodies against the sarcoplasmic reticular Ca(2+) ATPase (SERCA), the L-type calcium channel, the Na(+)/Ca(2+) exchanger or the Na(+)/K(+) ATPase.

RESULTS

Sepsis in the presence and absence of burn trauma increased [Ca(2+)](i) and [Na(+)](i). SERCA expression was decreased in the sepsis and burn plus sepsis groups while calcium channel expression was transiently increased in these sepsis groups. Na(+)/Ca(2+) exchanger expression exhibited a biphasic pattern of altered expression. Sepsis and burn plus sepsis reduced Na(+)/K(+) ATPase protein levels. These data suggest that altered transporter expression produce cardiomyocyte calcium and sodium loading and may contribute to sepsis-mediated cardiac contractile dysfunction.

Lipopolysaccharide activates calcineurin in ventricular myocytes

OBJECTIVES

We investigated whether lipopolysaccharide (LPS), a proximate cause of inflammation, activates calcineurin in cardiac myocytes and if calcineurin regulates apoptosis in this setting.

BACKGROUND

Calcineurin regulates myocardial growth and hypertrophy, but its role in inflammation is unknown. Calcineurin has proapoptotic or antiapoptotic effects depending on the stimuli.

METHODS

Calcineurin activity was measured in left ventricular myocytes from adult Sprague Dawley rats. Cardiac apoptosis was measured by terminal deoxy-nucleotidyl transferase-mediated dUTP nick end-labeling staining and caspase-3 activity after in vitro and in vivo exposure to LPS.

RESULTS

Lipopolysaccharide increased calcineurin activity in myocytes over 1 to 24 h (t 1/2 = 4.8 h) with an EC(50) of 0.80 ng/ml LPS (p < 0.05, n = 4). The LPS (10 ng/ml) effects were mimicked by angiotensin II (Ang II) (100 nmol/l); both increased calcineurin activity and induced apoptosis without additive effects (p < 0.05, n = 5 to 9). Lipopolysaccharide and/or Ang II effects were prevented by 1 h pre-treatment with an Ang II type 1 receptor blocker (losartan, 1 micromol/l), calcineurin inhibitor (cyclosporin A, 0.5 micromol/l), calcium chelator (1,2-Bis(2-amino-5-fluorophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl) ester, 0.1 micromol/l), or by inhibiting sarcoplasmic reticulum (SR) calcium (Ca)-ATPase (thapsigargin, 1 micromol/l) or SR calcium release channel (ryanodine, 1 micromol/l). Left ventricular apoptosis increased from 4 to 24 h after LPS (1 mg/kg intravenously) in vivo, but not in rats pre-treated with cyclosporin A (20 mg/kg/day subcutaneously) for 3 days (p < 0.05, n = 5).

CONCLUSIONS

In cardiac myocytes, LPS activates calcineurin in association with apoptosis by Ang II and SR calcium-dependent mechanisms. This expands the paradigm for cardiac calcineurin to be activated by low levels of LPS in inflammation and chronic conditions (e.g., infections, smoking, and heart failure).

Glibenclamide attenuates the antiarrhythmic effect of endotoxin with a mechanism not involving K(ATP) channels

The role of K(ATP) channels in the antiarrhythmic effect of Escherichia coli endotoxin-induced nitric oxide synthase (iNOS) was examined in an anesthetised rat model of myocardial ischemia and reperfusion arrhythmia by using glibenclamide (1 mg kg(-1)), nateglinide (10 mg kg(-1)) and repaglinide (0.5 mg kg(-1)). Endotoxin (1 mg kg(-1)) was administered intraperitoneally 4 h before the occlusion of the left coronary artery and glibenclamide, nateglinide or repaglinide was administered 30 min before coronary artery occlusion. We also evaluated the effects of K(ATP) channel blockers and nonselective K(+) channel blocker tetraethylammonium (TEA) on cardiac action potential configuration in the atria obtained from endotoxemic rats. The mean arterial blood pressure of rats receiving endotoxin was lower during both the occlusion and reperfusion periods. Endotoxin significantly reduced the total number of ectopic beats and the duration of ventricular tachycardia. Glibenclamide, but not nateglinide and repaglinide, prevented the hypotension and antiarrhythmic effects of endotoxin. Atria obtained from endotoxin-treated rats had prolonged action potential duration. This effect was abolished with pretreatment of iNOS inhibitors, l-canavanine and dexamethasone and perfusion of glibenclamide, but not with TEA and non-sulfonylurea drug, nateglinide. We demonstrated that glibenclamide inhibits the antiarrhythmic effect of endotoxin and this effect does not appear to involve K(ATP) channels.

Reversible Cardiomyopathy After Severe Burn Injury

Cardiomyopathy can result in significant morbidity and mortality, leading to long-term cardiac disability or consideration for transplantation. This study reviewed our experience with pediatric burn patients who developed cardiomyopathy during their acute hospitalization. We identified five patients admitted from 1991 to 2003 who were diagnosed with cardiomyopathy during their initial hospitalization and retrospectively collected data regarding hospital course, cardiac dysfunction, radiographic and echocardiographic studies, pharmacologic treatment, and long-term cardiac function. All children were Caucasian males with extensive full-thickness burns requiring prolonged ventilatory support. Initial signs and symptoms of cardiomyopathy, including radiographic and echocardiographic evidence, were noted greater than 30 days after injury. Patients received a combination of digoxin, diuretics, angiotensin-enzyme converting inhibitor, and beta-blocker therapy. During follow-up over the course of 2 to 11 years, all patients returned to normal cardiac function. Cardiomyopathy after extensive burn injury appears reversible. With prompt diagnosis and treatment, cardiac function normalizes within 9 to 21 months after the initiation of treatment.

Is there a role for cardiomyocyte toll-like receptor 4 in endotoxemia?

Lipopolysaccharide (LPS) is thought to be an important molecule in myocardial depression in sepsis. Toll-like receptor 4 (TLR4), the lipopolysaccharide receptor, is known to underlie these responses. Because TLR4 is expressed on both cardiac myocytes and immune cells, it is unclear as to which cell type is responsible for myocyte depression. In this article, we present evidence that the early response is likely related to TLR4 on immune cells and most likely macrophages, whereas the more delayed response may involve various immune cells as well as myocytes.

Probing a putative dantrolene-binding site on the cardiac ryanodine receptor

Dantrolene is an inhibitor of intracellular Ca2+ release from skeletal muscle SR (sarcoplasmic reticulum). Direct photoaffinity labelling experiments using [3H]azidodantrolene and synthetic domain peptides have demonstrated that this drug targets amino acids 590-609 [termed DP1 (domain peptide 1)] of RyR1 (ryanodine receptor 1), the skeletal muscle RyR isoform. Although the identical sequence exists in the cardiac isoform, RyR2 (residues 601-620), specific labelling of RyR2 by dantrolene has not been demonstrated, even though some functional studies show protective effects of dantrolene on heart function. Here we test whether dantrolene-active domains exist within RyR2 and if so, whether this domain can be modulated. We show that elongated DP1 sequences from RyR1 (DP1-2s; residues 590-628) and RyR2 (DP1-2c; residues 601-639) can be specifically photolabelled by [3H]azidodantrolene. Monoclonal anti-RyR1 antibody, whose epitope is the DP1 region, can recognize RyR1 but not RyR2 in Western blot and immunoprecipitation assays, yet it recognizes both DP1-2c and DP1-2s. This suggests that although the RyR2 sequence has an intrinsic capacity to bind dantrolene in vitro, this site may be poorly accessible in the native channel protein. To examine whether it is possible to modulate this site, we measured binding of [3H]dantrolene to cardiac SR as a function of free Ca2+. We found that > or =10 mM EGTA increased [3H]dantrolene binding to RyR2 by approximately 2-fold. The data suggest that the dantrolene-binding site on RyR2 is conformationally sensitive. This site may be a potential therapeutic target in cardiovascular diseases sensitive to dysfunctional intracellular Ca2+ release.

Polyethylene glycol-superoxide dismutase prevents endotoxin-induced cardiac dysfunction

RATIONALE

Sepsis produces significant mitochondrial and contractile dysfunction in the heart, but the role of superoxide-derived free radicals in the genesis of these abnormalities is not completely understood.

OBJECTIVES

The study was designed to test the hypothesis that superoxide scavenger administration prevents endotoxin-induced cardiac mitochondrial and contractile dysfunction.

METHODS

Four groups of rats were studied, and animals were injected with either saline, endotoxin, endotoxin plus polyethylene glycol-adsorbed-superoxide dismutase (PEG-SOD; a free-radical scavenger), or PEG-SOD alone. Animals were killed 48 h after injections. We then measured cardiac mitochondrial generation of reactive oxygen species (ROS), formation of free-radical reaction products (protein carbonyls, lipid aldehydes, nitrotyrosine), mitochondrial function, and cardiac contractile function.

MEASUREMENTS AND MAIN RESULTS

Endotoxin elicited increases in cardiac mitochondrial ROS formation (p < 0.001), increases in cardiac levels of free-radical reaction products, reductions in mitochondrial ATP generation (p < 0.001), and decrements in cardiac pressure-generating capacity (p < 0.01). Administration of PEG-SOD blocked formation of free-radical reaction products, prevented mitochondrial dysfunction, and preserved cardiac contractility. For example, mitochondrial ATP generation was 923 +/- 50, 392 +/- 32, 753 +/- 25, and 763 +/- 36 nmol/min/mg, respectively, for control, endotoxin, endotoxin + PEG-SOD, and PEG-SOD groups (p < 0.001). In addition, cardiac systolic pressure generation at a diastolic pressure of 15 mm Hg averaged 110 +/- 11, 66 +/- 7, 129 +/- 10 and 124 +/- 5 mm Hg, respectively, for control, endotoxin, endotoxin + PEG-SOD, and PEG-SOD groups (p < 0.01).

CONCLUSION

These data indicate that superoxide-derived oxidants play a critical role in the development of cardiac mitochondrial and contractile dysfunction in endotoxin-induced sepsis.

Effects of neutral sulfate berberine on LPS-induced cardiomyocyte TNF-alpha secretion, abnormal calcium cycling, and cardiac dysfunction in rats

AIM

To evaluate the effect of neutral sulfate berberine on cardiac function, tumor necrosis factor alpha (TNF-alpha) release, and intracellular calcium concentration ([Ca(2+)]i) in cardiomyocytes exposed to lipopolysaccharide (LPS).

METHODS

Primary cultured rat cardiomyocytes were prepared from ventricles of 3-4-day old Sprague-Dawley rats. TNF-alpha concentrations in cell-conditioned media were measured by using a Quantikine enzyme-linked immunosorbent assay kit, and cardiomyocyte [Ca(2+)]i was measured by using Fura-2/AM. The isolated rat hearts were perfused in the Langendorff mode.

RESULTS

LPS at doses of 1, 5, 10, and 20 microg/mL markedly stimulated TNF-alpha secretion from cardiomyocytes, and neutral sulfate berberine inhibited LPS-induced TNF-alpha production. Intracellular calcium concentration was significantly decreased after LPS stimulation for 1 h, and increased 2 h after LPS treatment. Pretreatment with neutral sulfate berberine reversed the LPS-induced [Ca(2+)]i alterations, although neutral sulfate berberine did not inhibit a rapid increase in cardiomyocyte [Ca(2+)]i induced by LPS. Perfusion of isolated hearts with LPS (100 microg/mL) for 20 min resulted in significantly impaired cardiac performance at 120 min after LPS challenge: the maximal rate of left ventricular pressure rise and fall (+/-dp/dt(max)) decreased compared with the control. In contrast, +/-dp/dt(max) at 120 min in hearts perfused with neutral sulfate berberine (1 micromol/L) for 10 min followed by 20 min LPS (100 microg/mL) was greater than the corresponding value in the LPS group.

CONCLUSION

Neutral sulfate berberine inhibits LPS-stimulated myocardial TNF-alpha production, impairs calcium cycling, and improves LPS-induced contractile dysfunction in intact heart.

Nitric oxide modifies the sarcoplasmic reticular calcium release channel in endotoxemia by both guanosine-3',5' (cyclic) phosphate-dependent and independent pathways

OBJECTIVES

a) To determine whether decreased sarcoplasmic calcium release channel (CRC) activity is a mechanism by which myocardial contractility is reduced in endotoxemia; b) to determine whether nitric oxide modulates CRC activity in endotoxemia; and c) to examine two nitric oxide signaling pathways in relation to CRC function in endotoxemia.

DESIGN

Randomized, prospective using a rat model of endotoxemia.

SETTING

: Research laboratory.

SUBJECTS

Sprague-Dawley rats.

INTERVENTIONS

Endotoxemia was induced by lipopolysaccharide administration. The effects of nitric oxide were studied using the highly selective inducible nitric oxide synthase inhibitor N-(3-(aminomethyl)benzyl)acetamidine dihydrochloride (1400W) and the specific guanylyl cyclase inhibitor 1-H (1, 2, 4)oxadiazolo[4,3-a]quinoxalin-1-one (ODQ).

MEASUREMENTS AND MAIN RESULTS

We assessed myocardial contractility, myocardial nitric oxide content, and guanosine-3',5' (cyclic) phosphate (cGMP) content. We determined CRC activity by calcium release and ryanodine binding assays. We followed these variables at four time points through the course of endotoxemia. We found that myocardial contractility and CRC activity were decreased in late but not in early endotoxemia. Furthermore, inducible nitric oxide synthase inhibition with 1400W restored contractility and CRC activity in late endotoxemia but paradoxically worsened these variables in early endotoxemia. Through the use of the guanylyl cyclase inhibitor ODQ, we demonstrate that nitric oxide acts through cGMP-mediated mechanisms in early and late endotoxemia. We investigated cGMP-independent pathways by assessing the oxidative status of the CRC. We found that in late endotoxemia, nitric oxide decreased the number of free thiols, demonstrating that nitric oxide also acts through cGMP-independent pathways.

CONCLUSIONS

Nitric oxide has a dual effect on the CRC in endotoxemia. At low concentrations, as measured in early endotoxemia, nitric oxide stabilizes the CRC through cGMP-mediated mechanisms. In late endotoxemia, high nitric oxide concentrations decrease channel activity through both cGMP-dependent and cGMP-independent mechanisms.

Sepsis and myocardial depression in a young woman

Severe sepsis may be associated with depression of myocardial function, attributed to various inflammatory mediators. Myocardial dysfunction in sepsis is characterized by biventricular failure and complicates usual therapy with high-volume fluid resuscitation and vasopressors. However, in patients who survive septic shock, myocardial dysfunction can improve rapidly. We describe a young woman with septic shock due to Streptococcus pneumoniae, complicated by severe but reversible biventricular dysfunction.

Tumor necrosis factor-alpha-induced caspase activation mediates endotoxin-related cardiac dysfunction

OBJECTIVE

Sepsis-induced cardiac dysfunction is a serious clinical syndrome characterized by hypotension, decreased systemic vascular resistance, and elevated cardiac index. Although cytokines such as tumor necrosis factor (TNF)-alpha have been shown to play a significant role early in this response, the downstream effects of TNF-alpha signaling on cardiac function, specifically its relationship to apoptosis, have not been fully elucidated.

DESIGN

Previous studies from our laboratory have identified endotoxin-induced apoptosis in cardiac cells in vitro. To further determine the role of lipopolysaccharide-induced apoptosis in vivo, mice were injected intraperitoneally with lipopolysaccharide (4 mg/kg), and cardiac apoptosis was detected and inhibited using a broad-spectrum caspase inhibitor.

SETTING

University research laboratory.

SUBJECTS

Adult male wild-type (B6:129PF1/J) and TNF receptor 1/receptor 2 (TNFR-1/2) knockout mice (B6;129S-Tnfrsf1aTnfrsf1b).

INTERVENTIONS

We sought to determine the dependence of cardiac apoptosis on TNF-alpha signaling and determine the physiologic role of caspase activation on lipopolysaccharide-induced cardiac dysfunction.

MEASUREMENTS AND MAIN RESULTS

Cardiac apoptosis was determined at baseline and at 2, 4, 8, and 24 hrs by detection of capase-3 and -8 activity, cytoplasmic levels of Bax/Bcl-2, cleaved caspase-3 immunohistochemistry, and terminal deoxynucleotidyl transferase UTP nick-end labeling (TUNEL) staining of histologic sections in wild-type and TNFR-1/2 knockout mice. To determine the role of caspase activation in lipopolysaccharide-induced cardiac dysfunction, a broad-spectrum caspase inhibitor Z-Val-Ala-Asp (ome)-FMK (sad) was given, and cardiac function was determined in isolated beating hearts (Langendorff preparation). Our experiments determined that caspase-3-dependent apoptosis was active in cardiac tissue by 2 hrs and that this activation was completely mediated by TNFR-1/2. The Bax/Bcl-2 ratios supported the finding and time course of apoptosis, whereas TUNEL staining of cardiac tissue sections identified sporadic apoptotic ventricular cells. The administration of zVAD significantly inhibited myocardial caspase-3 activity and preserved cardiac physiologic function (Langendorff preparation).

CONCLUSIONS

Endotoxin induces a TNF-alpha-dependent apoptotic cascade in the myocardium, which contributes to the development of cardiac dysfunction.

Increased leakage of sarcoplasmic reticulum Ca2+ contributes to abnormal myocyte Ca2+ handling and shortening in sepsis*

OBJECTIVE

Changes in cardiac function due to sepsis have been widely reported. However, the underlying mechanisms remain poorly understood. In the mammalian heart, myocyte function and intracellular calcium homeostasis are closely coupled. In this study we tested the hypothesis that alterations in cardiac calcium homeostasis due to sepsis underlie the observed myocyte dysfunction.

DESIGN

Randomized prospective animal study.

SETTING

Research laboratory.

SUBJECTS

Male Sprague-Dawley rats weighing 250-275 g.

INTERVENTIONS

We induced sepsis by cecal ligation and puncture in the rat, which mimics the type of infection caused by perforation of the intestine in humans.

MEASUREMENTS AND RESULTS

Forty-eight hours after cecal ligation and puncture, isolated cardiac ventricular cardiomyocytes demonstrated a 57% decreased peak systolic [Ca]. The time constant of the Ca transient increased 71% and 57% in myocytes obtained 24 hrs and 48 hrs after cecal ligation and puncture, respectively. The average shortening of cardiomyocytes 48 hrs after cecal ligation and puncture was significantly decreased. To investigate the cellular mechanisms of altered Ca transients and myocyte shortening, we measured Ca sparks, the spontaneous local Ca release events in cardiomyocytes at resting states. The Ca spark frequency progressively increased in myocytes 24 hrs and 48 hrs after cecal ligation and puncture. The total activity of sparks also increased compared with sham-operated animals. The overall leakage of sarcoplasmic reticulum Ca in resting states was increased in sepsis and resulted in reduced sarcoplasmic reticulum Ca content.

CONCLUSIONS

Abnormal Ca leakage from the sarcoplasmic reticulum contributes significantly to the depressed myocyte shortening in sepsis. In the future, modalities that prevent this Ca leakage may prove beneficial in the treatment of sepsis-induced myocyte shortening.

Burn trauma alters calcium transporter protein expression in the heart

We have shown previously that burn trauma produces significant cardiac dysfunction, which is first evident 8 h postburn and is maximal 24 h postburn. Because calcium handling by the cardiomyocyte is essential for cardiac function, one mechanism by which burn injury may cause cardiac abnormalities is via calcium dyshomeostasis. We hypothesized that major burn injury alters cardiomyocyte calcium handling through changes in calcium transporter expression. Sprague-Dawley rats were given either burn injury or no burn injury (controls). Cardiomyocyte intracellular calcium and sodium were quantified at various times postburn by fura 2-AM or sodium-binding benzofuran isophthalate fluorescent indicators, respectively. In addition, hearts freeze-clamped at various times postburn (2, 4, 8, and 24 h) were used for Western blot analysis using antibodies against the sarcoplasmic reticulum calcium-ATPase (SERCA), the L-type calcium-channel, the ryanodine receptor, the sodium/calcium exchanger, or the sodium-potassium-ATPase. Intracellular calcium levels were elevated significantly 8-24 h postburn, and intracellular sodium was increased significantly 4 through 24 h postburn. Expression of SERCA was significantly reduced 1-8 h postburn, whereas L-type calcium-channel expression was diminished 1 and 2 h postburn (P < 0.05) but returned toward control levels 4 h postburn. Ryanodine receptor protein was significantly reduced at 1 and 2 h postburn, returning to baseline by 4 h postburn. Sodium/calcium exchanger expression was significantly elevated 2 h postburn but was significantly reduced 24 h postburn. An increase in sodium-potassium-ATPase expression occurred 2-24 h postburn. These data confirm that burn trauma alters calcium transporter expression, likely contributing to cardiomyocyte calcium loading and cardiac contractile dysfunction.

ICAM-1 and VCAM-1 mediate endotoxemic myocardial dysfunction independent of neutrophil accumulation

Both intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) have been implicated in neutrophil-mediated lung and liver injury during sepsis. However, the role of these adhesion molecules as well as the contribution of neutrophils in myocardial dysfunction during sepsis remains to be determined. The purpose of this study was to examine the role of ICAM-1, VCAM-1, and neutrophils in lipopolysaccharide (LPS)-induced myocardial dysfunction. Mice were subjected to LPS (0.5 mg/kg ip) or vehicle (normal saline), and left ventricular developed pressure (LVDP) was determined by the Langendorff technique. LVDP was depressed by nearly 40% at 6 h after LPS. Immunofluorescent staining revealed a temporal increase in myocardial ICAM-1/VCAM-1 expression and neutrophils after LPS. Antibody blockade of VCAM-1 reduced myocardial neutrophil accumulation and abrogated LPS-induced cardiac dysfunction. Antibody blockade or absence of ICAM-1 (gene knockout) also abrogated LPS-induced cardiac dysfunction but did not reduce neutrophil accumulation. Neutrophil depletion (vinblastine or antibody) did not protect from LPS-induced myocardial dysfunction. Our results suggest that although endotoxemic myocardial dysfunction requires both ICAM-1 and VCAM-1, it occurs independent of neutrophil accumulation.

Cardiomyocyte intracellular calcium and cardiac dysfunction after burn trauma

OBJECTIVE

To examine the effects of pharmacologic agents designed to limit burn-mediated calcium overload on cardiomyocyte [Ca2+] and cardiac contractile function.

DESIGN

Experimental, comparative study.

SETTING

Cellular biology and physiology laboratory.

SUBJECTS

Adult Sprague Dawley rats.

INTERVENTIONS

Rats were given third-degree burn injury over 40% of the total body surface area, were fluid resuscitated, and then were divided randomly to receive one of five treatments: vehicle (normal saline); amiloride (50 mg/kg) to inhibit H+-Na+ exchange and subsequent Na+-Ca2+ exchange; dantrolene (10 mg/kg, 30 mins, 6 and 22 hrs postburn) to inhibit sarcoplasmic reticulum Ca2+ release; diltiazem (10 mg/kg given over first 6 hrs postburn); or amlodipine (0.07 mg/kg, 24 hrs preburn and 30 mins postburn) to block calcium slow channels. Appropriate controls (sham burns given the appropriate pharmacologic agent) were included in each group. Twenty-four hrs postburn, left ventricular function (Langendorff), cardiomyocyte [Ca2+]i and [Na+]i measured by fura-2-AM or sodium-binding benzofurzan isophthalate loading of cardiomyocytes, and myocyte secretion of tumor necrosis factor-alpha (enzyme-linked immunosorbent assay) were assessed in shams and burns from each experimental group. This time point was selected based on our previous work confirming maximal ventricular contractile defects and maximal cytokine secretion 24 hrs postburn.

MEASUREMENTS AND MAIN RESULTS

Burn trauma increased myocyte [Ca2+]i and [Na+]i, promoted tumor necrosis factor-alpha secretion by cardiomyocytes, and impaired left ventricular function. All pharmacologic agents reduced the burn-mediated Ca2+/Na+ accumulation in cardiomyocytes and ablated burn-mediated tumor necrosis factor-alpha secretion by myocytes; in contrast, dantrolene and amiloride provided significantly greater cardioprotection than pharmacologic agents that specifically targeted Ca2+ slow channels (diltiazem and amlodipine).

CONCLUSION

Our data suggest that the calcium antagonists used in this study provide cardioprotection by modulating several aspects of the overall inflammatory cascade rather than solely limiting cardiomyocyte accumulation of calcium.