Anthrax lethal toxin induces acute diastolic dysfunction in rats through disruption of the phospholamban signaling network.

BACKGROUND: Anthrax lethal toxin (LT), secreted by Bacillus anthracis, causes severe cardiac dysfunction by unknown mechanisms. LT specifically cleaves the docking domains of MAPKK (MEKs); thus, we hypothesized that LT directly impairs cardiac function through dysregulation of MAPK signaling mechanisms. METHODS AND RESULTS: In a time-course study of LT toxicity, echocardiography revealed acute diastolic heart failure accompanied by pulmonary regurgitation and left atrial dilation in adult Sprague-Dawley rats at time points corresponding to dysregulated JNK, phospholamban (PLB) and protein phosphatase 2A (PP2A) myocardial signaling. Using isolated rat ventricular myocytes, we identified the MEK7-JNK1-PP2A-PLB signaling axis to be important for regulation of intracellular calcium (Ca(2+)(i)) handling, PP2A activation and targeting of PP2A-B56α to Ca(2+)(i) handling proteins, such as PLB. Through a combination of gain-of-function and loss-of-function studies, we demonstrated that over-expression of MEK7 protects against LT-induced PP2A activation and Ca(2+)(i) dysregulation through activation of JNK1. Moreover, targeted phosphorylation of PLB-Thr(17) by Akt improved sarcoplasmic reticulum Ca(2+)(i) release and reuptake during LT toxicity. Co-immunoprecipitation experiments further revealed the pivotal role of MEK7-JNK-Akt complex formation for phosphorylation of PLB-Thr(17) during acute LT toxicity. CONCLUSIONS: Our findings support a cardiogenic mechanism of LT-induced diastolic dysfunction, by which LT disrupts JNK1 signaling and results in Ca(2+)(i) dysregulation through diminished phosphorylation of PLB by Akt and increased dephosphorylation of PLB by PP2A. Integration of the MEK7-JNK1 signaling module with Akt represents an important stress-activated signalosome that may confer protection to sustain cardiac contractility and maintain normal levels of Ca(2+)(i) through PLB-T(17) phosphorylation.

Echocardiographic effects of eplerenone and aldosterone in hypertensive rats.

The effects of aldosterone receptor blockade on echocardiography in spontaneously hypertensive rats (SHR) are not fully characterized. In this study, multiple echocardiographic parameters were compared for 42 weeks between SHR versus Wistar-Kyoto rats (WKY) serving as normotensive controls. In addition, echocardiographic parameters were compared for 28 weeks between the SHR versus SHR treated with eplerenone 100 mg/kg/day or spironolactone 50 mg/kg/day. Compared to normotensive WKY rats, SHRs had significantly increased systolic blood pressure, increased cardiac mass, increased isovolumic relaxation time (IVRT), decreased E/A ratio, increased mitral closure opening time interval (MCO) and increased Tei index. Both eplerenone and spironolactone significantly decreased systolic blood pressure compared to the SHR controls. The spironolactone treatment group demonstrated significant increases in heart rate and cardiac output and a decrease in cardiac index compared to SHR controls. Any aldosterone blockade in SHR protected against the increased cardiac mass. Similar to clinical echocardiographic observations, hypertension in rats results in left ventricular hypertrophy (LVH) and diastolic dysfunction and aldosterone receptor blockade reduces LVH in SHR.

Norepinephrine induces systolic failure and inhibits antiapoptotic genes in a polymicrobial septic rat model.

AIMS: We examined the effect of norepinephrine (NE) infusion on left ventricular function and apoptotic genes during progression of polymicrobial sepsis. METHODS: Male Sprague-Dawley rats (350-400 g) were made septic by intraperitoneal (i.p.) administration of 200mg/kg cecal inoculum. Sham animals received 5% dextrose water, i.p. Echocardiography was performed at baseline, 3 days and 7 days post-sepsis/sham. NE (0.6 µgkg(-1)h(-1)) was infused for 2h, before the end of day 3 of echocardiography. At the end of day 7, rats were euthanized and heart tissues harvested for isolation of total RNA. PCR was performed using RT(2) profiler™ PCR array PARN-012 (Rat apoptosis array; SuperArray, MD) using RT(2) Real-Time™ SYBR Green PCR master mix PA-012. KEY FINDINGS: NE-infusion resulted in a significant decrease in the left ventricular ejection fraction (EF) (62.56±2.07 from the baseline 71.11±3.23, p<0.05) and fractional shortening (FS) (39.90±2.64 from the sham group 54.41±2.19, p<0.05) at 7 days post-sepsis, respectively. Super Array data revealed that during sepsis, tumor necrosis factor (TNF-α) (2.85±0.07 fold, p<0.0001), anti-apoptotic molecules, Prok2 (16.07±0.48 fold, p<0.0001) and interleukin-10 (IL-10) (23.5±0.57 fold, p<0.0001) were up regulated at day 1. At 7-days post-sepsis, CD40l g (2.49±0.54 fold, p<0.08) and Birc1b (17.8±0.58 fold, p<0.0001) were up regulated compared to the sham, 1 and 3-days post-sepsis groups. SIGNIFICANCE: The data suggest that upregulation of a series of pro-apoptotic molecules could be responsible for systolic and diastolic dysfunction during 3 and 7 days post sepsis.

Enhanced external counterpulsation is a regenerative therapy.

Enhanced external counterpulsation (EECP) is used for the treatment of severe angina and heart failure in patients who are not candidates for revascularization. The clinical benefits of EECP extend well beyond the time period of any hemodynamic effects, but the cause of this prolonged effect is not understood. The prolonged clinical benefits suggest EECP could be a regenerative therapy. This study was performed to determine whether EECP increased circulating hematopoietic progenitor cells (HPCs) or endothelial progenitor cells (EPCs) and thus be a possible regenerative therapy. The proposed mechanism of the increase in regenerative circulating stem cells is the enhanced shear forces induced on the endothelial boundary by the flow reversal produced by the sequential inflation of the pneumatic cuffs during EECP therapy.

Integrins and proximal signaling mechanisms in cardiovascular disease.

Integrins are heterodimeric cell-surface molecules, which act as the principle mediators of molecular dialog between a cell and its extracellular matrix environment. In addition to their structural functions, integrins mediate signaling from the extracellular space into the cell through integrin-associated signaling and adaptor molecules such as FAK (focal adhesion kinase), ILK (integrin-linked kinase), PINCH (particularly interesting new cysteine-histidine rich protein) and Nck2 (non-catalytic (region of) tyrosine kinase adaptor protein-2). Via these molecules, integrin signaling tightly and cooperatively interacts with receptor tyrosine kinases (RTKs) signaling to regulate survival, proliferation and cell shape as well as polarity, adhesion, migration and differentiation. In the heart and blood vessels, the function and regulation of these molecules can be partially disturbed and thus contribute to cardiovascular diseases such as cardiac hypertrophy and atherosclerosis. In this review, we discuss the primary mechanisms of action and signaling of integrins in the cardiac and vascular system in normal and pathological states, as well as therapeutic strategies for targeting these systems (1).

Anthrax toxin: pathologic effects on the cardiovascular system.

Anthrax is a disease caused by infection with spores from the bacteria Bacillus anthracis. After entering the body, the spores germinate into bacteria and secrete a toxin that causes local edema and, in systemic infections, cardiovascular collapse and death. The toxin is a tripartite polypeptide, consisting of protective antigen (PA), lethal factor (LF) and edema factor (EF), which have key roles in the bacterial pathogenesis and disease progression. PA facilitates transfer of LF and EF to the cytosol. Lethal toxin is a zinc metalloproteinase, which has the capacity to inactivate mitogen-activated protein (MAP) kinase kinase (MEK) and stimulates the release of sepsis-related cytokines tumor necrosis factor-alpha and interleukin-1beta. Edema factor is a calmodulin (CaM)-dependent adenylate cyclase, which increases levels of cyclic AMP, causing impaired neutrophil function and disruption of water balance that ultimately results in massive tissue edema. Together, the toxins effectively inhibit host innate and adaptive immune responses, allowing the bacteria to grow unrestrained and overwhelming any resistance. Clinically, inhalational anthrax presents in a biphasic pattern with initial nonspecific "flu-like" symptoms nausea and vomiting 1 to 4 days after exposure, followed by severe illness with dyspnea, high fever and circulatory shock. The latter symptoms represent a terminal stage and treatment is often ineffective when started at that time. Key indicators of early anthrax cardiovascular-related pathogenesis include mediastinal widening in association with pleural effusion and edema. In this review, we describe the current understanding of anthrax toxins on cellular function in the context of cardiovascular function and discuss potential therapeutic strategies.

Guidewire pacing safely and effectively treats bradyarrhythmias induced by rheolytic thrombectomy and precludes the need for transvenous pacing: the Scott & White experience.

Rheolytic thrombectomy (RT) is useful in certain percutaneous coronary interventions but may be associated with transient bradyarrhythmias. Clinicians have devised numerous strategies to deal with these arrhythmias apart from transvenous right ventricular pacing, some of which are described in other parts of this supplement. We report the Scott & White experience utilizing guidewire pacing to quickly and safely pace the heart in the event of bradyarrhythmia. We found this method to be safe and reliable (96.2% successful) during RT and now use this technique almost exclusively in the cardiac catheterization lab to deal with transient bradyarrhythmias during RT or due to any other cause.We also report an increased incidence of bradyarrhythmia occurring during RT when it is performed in the right coronary artery, with a trend toward an increased incidence during the clinical presentation of ST-elevation myocardial infarction.

Anthrax toxins induce shock in rats by depressed cardiac ventricular function.

Anthrax infections are frequently associated with severe and often irreversible hypotensive shock. The isolated toxic proteins of Bacillus anthracis produce a non-cytokine-mediated hypotension in rats by unknown mechanisms. These observations suggest the anthrax toxins have direct cardiovascular effects. Here, we characterize these effects. As a first step, we administered systemically anthrax lethal toxin (LeTx) and edema toxin (EdTx) to cohorts of three to twelve rats at different doses and determined the time of onset, degree of hypotension and mortality. We measured serum concentrations of the protective antigen (PA) toxin component at various time points after infusion. Peak serum levels of PA were in the microg/mL range with half-lives of 10-20 minutes. With doses that produced hypotension with delayed lethality, we then gave bolus intravenous infusions of toxins to groups of four to six instrumented rats and continuously monitored blood pressure by telemetry. Finally, the same doses used in the telemetry experiments were given to additional groups of four rats, and echocardiography was performed pretreatment and one, two, three and twenty-four hours post-treatment. LeTx and EdTx each produced hypotension. We observed a doubling of the velocity of propagation and 20% increases in left ventricular diastolic and systolic areas in LeTx-treated rats, but not in EdTx-treated rats. EdTx-but not LeTx-treated rats showed a significant increase in heart rate. These results indicate that LeTx reduced left ventricular systolic function and EdTx reduced preload. Uptake of toxins occurs readily into tissues with biological effects occurring within minutes to hours of serum toxin concentrations in the microg/mL range. LeTx and EdTx yield an irreversible shock with subsequent death. These findings should provide a basis for the rational design of drug interventions to reduce the dismal prognosis of systemic anthrax infections.

Lethal and edema toxins of anthrax induce distinct hemodynamic dysfunction.

Fatalities due to anthrax are associated with severe hypotension suggesting that the toxins generated from Bacillus anthracis, lethal toxin (LeTx) and edema toxin (EdTx), have cardiovascular effects. Here, we demonstrate the effects of these toxins and characterize their effects by echocardiography. LeTx leads to a significant reduction in ejection fraction, decreased velocity of propagation (diastolic dysfunction), decreased velocity of circumferential fiber shortening (decreased contractility), and increased LV systolic area (pathophysiology). EdTx leads to a significant reduction in left ventricular volumes and cardiac output (reduced stroke volume) but does not cause significant change in ejection fraction or contractility. These results indicate that LeTx reduces left ventricular systolic function and EdTx reduces preload but does not have direct myocardial effects. Together, these findings suggest that LeTx and EdTx exert distinct hemodynamic dysfunction associated with anthrax infection.

Integrins: novel therapeutic targets for cardiovascular diseases.

Integrins are the principle mediators of molecular dialog between a cell and its extracellular matrix environment. The unique combinations of integrin subunits determine which extracellular matrix molecules are recognized by a cell. Recent studies have demonstrated that remodeling in heart and vasculature is linked to alterations in extracellular matrix and integrin expression. The roles of integrins in controlling cellular behavior have made these molecules highly attractive drug targets. New insights into mechanisms whereby the extracellular matrix takes part in the control of smooth muscle cell proliferation and cardiac growth suggest a number of putative targets for future therapies that can be applied to increase plaque stability, prevent the clinical consequences of atherosclerosis and improve outcomes after interventional procedures such as cardiac transplantation. Therapeutic candidates include antibodies, cyclic peptides, peptidomimetics and small molecules. The integrin inhibitors Integrilin and ReoPro have been approved as blood thinners in cardiovascular disease, and newer agents are undergoing testing. Although integrin function is important in the cardiovascular system, there are wide gaps in knowledge. In this review, we discuss the primary mechanisms of action and signaling of integrins in the cardiac and vascular system in normal and pathological states, as well as therapeutic strategies for targeting these molecules in the cardiovascular system.

Cyclooxygenase-2 inhibitors: a painful lesson.

Non-steroidal anti-inflammatory drugs (NSAIDs) represent a clinically important class of agents. NSAIDs are commonly used in treatment of conditions such as headache, fever, inflammation and joint pain. Complications often arise from chronic use of NSAIDs. Gastrointestinal (GI) toxicity in the form of gastritis, peptic erosions and ulcerations and GI bleeds limit usage of NSAIDs. These toxicities are thought to be due to cyclooxygenase (COX)-1 blockade. COX-1 generates cytoprotective prostanoids such as prostaglandin (PG) E2 and prostacyclin (PGI2). COX-2 inhibitors, commonly referred to as coxibs, were developed to inhibit inflammatory prostanoids without interfering with production of COX-1 prostanoids. Concerns over cardiovascular safety, however, have evolved based on the concept of inhibition of COX-2-derived endothelial prostanoids without inhibition of platelet thromboxane A2, leading to increased cardiovascular risk. The Celecoxib Long-Term Arthritis Safety Study (CLASS) trial did not show a significant increase in cardiovascular risk for celecoxib (Celebrex), but results of the Vioxx Gastrointestinal Outcomes Research (VIGOR) study showed an increased cardiovascular risk with long-term daily usage of rofecoxib in patients with rheumatoid arthritis. The Adenomatous Poly Prevention on Vioxx (APPROVe) trial further evaluated cardiovascular effects of rofecoxib and recently led to removal of this drug from the marketplace. Coxibs affect renal function via blockade of normal COX-2 functions. COX-2 expression increases in high renin states and in response to a high-sodium diet or water deprivation. PGI2 and PGE2 are the most important renal prostanoids. PGI2 inhibition results in hyperkalemia. PGE2 inhibition results in sodium retention, which leads to hypertension, peripheral edema and potentially exacerbation of heart failure. This review article discusses beneficial and deleterious effects associated with prostanoids produced by COX-1 and COX-2 in various organs and how blockade of these products translates into clinical medicine.

Aldosterone receptor antagonists and cardiovascular disease: do we need a change of the guard?

Aldosterone is a mineralocorticoid primarily produced in the zona glomerulosa of the adrenal gland. For many years, aldosterone (Aldo) was thought to have its sole site of action in the kidney, where it regulated sodium excretion and potassium reabsorption. It is now known that Aldo is produced in cardiovascular tissues, and has been implicated in the development of ventricular hypertrophy and cardiac fibrosis. The precise mechanisms whereby Aldo acts in cardiac tissues are diverse. It was assumed that Aldo production could be limited by angiotensin-converting enzyme (ACE) inhibition, but serial measurements during therapy reveal only a transient decrease in Aldo levels. Moreover, the effects of Aldo on cardiac tissues occur even when angiotensin II (Ang II) has been suppressed or eliminated. Multiple investigators have examined effects of Aldo receptor blockade in human subjects and various animal models using the two Aldo receptor antagonists (ARAs), spironolactone and eplerenone. Major clinical trials involving spironolactone (RALES) and eplerenone (EPHESUS) ARAs have shown significant benefits in the treatment of congestive heart failure (CHF). In RALES, patients with New York Heart Association (NYHA) Class III or IV systolic heart failure treated with spironolactone had a 30% relative risk decrease in mortality. Although spironolactone is an effective competitive inhibitor of the mineralocorticoid receptor (MR), progestational and antiandrogenic side effects limit its use in some patients. Eplerenone, a more selective ARA, lacks these undesirable side effects. Although eplerenone is 20-fold less potent at the MR, it demonstrates efficacy similar to spironolactone, possibly due to decreased protein binding. Eplerenone has fewer side effects than spironolactone, which has been attributed to the low cross-reactivity with androgen and progesterone receptors. In EPHESUS, patients with left ventricular systolic dysfunction [Ejection Fraction (EF) <40%] and CHF following an acute myocardial infarction (AMI), were treated with eplerenone, resulting in a 17% reduction in cardiovascular mortality. However, these studies were limited in that diastolic function was not evaluated, although approximately 1/2 of CHF is due to diastolic dysfunction alone. To date, neither ARA has been studied for the treatment of diastolic dysfunction in a major clinical trial. However, numerous animal studies employing ARAs have shown a decrease in cardiac hypertrophy and fibrosis, indicating the potential benefits of these agents in the treatment of diastolic heart failure. In this review, we discuss possible underlying mechanisms responsible for Aldo effects on cardiovascular function and compare the beneficial effects of spironolactone and eplerenone in the treatment of heart disease.

Baseline echocardiographic values for adult male rats.

BACKGROUND: Because of safety, repeatability, and portability, clinical echocardiography is well established as a standard for cardiac anatomy, cardiac function, and hemodynamics. Similarly, application of echocardiography in commonly used rat experimental models would be worthwhile. The use of noninvasive ultrasound imaging in the rat is a potential replacement for more invasive terminal techniques. Although echocardiography has become commonly used in the rat, normal parameters for cardiac anatomy and function, and comparison with established human values, have not been reported. METHODS: A total of 44 Sprague-Dawley male rats had baseline echocardiography replicating a protocol for clinical echocardiography. RESULTS: Complete 2-dimensional echocardiography for cardiac anatomy and function was obtained in 44 rats. Hemodynamic parameters could be recorded in 85% of rats. The ejection fraction and fractional shortening values of the left ventricle were similar to those reported for healthy human beings. Pulsed Doppler velocities of atrial systole for mitral valve inflow, pulmonary vein reversal, and Doppler tissue of the lateral mitral valve annulus also had similar means as healthy human beings. The calculated left ventricular mass was at the same order of magnitude as a proportion of body weight of rat to man. All other observations in the clinical protocol were different from those reported in healthy human beings. CONCLUSION: The use of echocardiography for assessment of cardiac anatomy, function, and hemodynamics can be consistently applied to the rat and replicates much of the information used routinely in human echocardiography.

Comparison of lipid and non-lipid markers of atherosclerosis in arterial versus venous blood.

BACKGROUND: Early studies have suggested that there may be differences in the concentration of lipoprotein particles and their associated apolipoproteins in arterial and venous blood and that this gradient might explain a proclivity to develop atherosclerotic lesions. The aim of this study was to use current methods of analysis to determine levels of these components, including particle densities and several common inflammatory markers in arterial and venous blood. METHODS: Samples of arterial and venous blood were obtained nearly simultaneously in 26 patients undergoing right and left heart catheterization. Analyses were performed using enzymatic, immunoturbidimetric and ultracentrifugation assays. RESULTS: Data obtained for total cholesterol, triglyceride, HDL-cholesterol, LDL-cholesterol, HDL and LDL particle density, high sensitivity C-reactive protein, serum amyloid-A and apoprotein B-100 concentrations in arterial and venous blood did not demonstrate any significant difference in the means. CONCLUSION: Arterial and venous blood can be used interchangeably to study the effect of blood concentrations of common soluble surrogate markers of atherosclerosis.

Single coronary artery with an ectopic origin and interarterial course: a case report and review of the literature.

A previously unreported variant of a single coronary artery arising between the aorta and pulmonary artery is presented. This variant had many high-risk features, so prophylactic coronary artery bypass grafting was recommended.

Intravenous immunoglobulin-related acute coronary syndrome and coronary angiography in idiopathic thrombocytopenic purpura--a case report and literature review.

In acute coronary syndromes, GPIIb/IIIa platelet inhibitors have demonstrated a reduction in recurrent myocardial ischemia. Conversely, one might expect that enhancing platelet activity in patients in acute coronary syndromes would have the opposite effect. We report a patient with idiopathic thrombocytopenic purpura (ITP) that had recurrent myocardial ischemia associated with administration of intravenous immunogloblin (IVIG). Literature is reviewed.