Citations

Background —Endothelin-converting enzyme-1 (ECE-1) processes big endothelin-1 (ET-1) to ET-1, a peptide implicated in atheroma formation. ECE-1 exists in 2 isoforms (ECE-1α and ECE-1β), the result of alternative splicing of a common gene. Neutral endopeptidase (NEP) is a genetically distinct metallopeptidase that degrades the natriuretic peptides. These peptides mediate antiproliferative and vasodilating actions. We sought to demonstrate the distribution of the 2 ECE-1 isoforms in experimental atherosclerosis, to determine the effects of chronic NEP-I on plasma cGMP concentrations, vascular wall ECE-1 activity, and ET-1 concentration, and to correlate these actions with atheroma formation. Our hypothesis was that chronic NEP-I, in association with augmented cGMP, would inhibit ECE-1 conversion of big ET-1 to active ET-1, thus reducing tissue ET-1 concentrations and associated atheroma formation. Methods and Results —Cholesterol-fed New Zealand White rabbits (n=8, 1% cholesterol diet) and NEP-I–treated cholesterol-fed New Zealand White rabbits (n=8; candoxatril, 30 mg/kg per day, Pfizer) were euthanized after 8 weeks of feeding. ECE-1α and ECE-1β immunoreactivity was present in the aortas of both groups. Compared with control values, plasma cGMP concentrations were increased (2.8±0.6 versus 8.4±1.2 pmol/mL, P <0.05), ECE-1 activity was attenuated (68±3% versus 32±8%, P <0.05), aortic tissue ET-1 concentrations were reduced (4.6±0.5 versus 3.2±0.3 pg/mg protein, P <0.05), and atheroma formation was attenuated (62±6% versus 34±5%, P <0.01) by NEP-I. Conclusions —These studies suggest that ECE-1 is present and functionally active in the vascular wall in atherosclerosis. Inhibition of ECE-1 by NEP-I represents a novel approach to interruption of the endothelin system in this cardiovascular disease state.

Background —Interaction of complement with endothelial cells (ECs) underlies the development of inflammation and coagulation in disease. Assembly of the membrane attack complex (MAC) of complement on EC membrane, like stimulation with cytokines, upregulates tissue factor and cyclooxygenase-2 but does so via the intermediary action of IL-1α. We asked whether the MAC activates porcine aortic and microvascular ECs in a global manner by this mechanism and whether this mechanism is used by membrane pore-forming structures. Methods and Results —Exposure of ECs to complement caused upregulation of mRNAs for E-selectin, intracellular adhesion molecule-1, vascular cell adhesion molecule-1, Iκ-Bα, interleukin (IL)-1α, IL-1β, IL-8, and plasminogen activator inhibitor-1 over a period of 6 hours. The expression of these genes was not a primary response to stimulation, however, because IL-1 receptor antagonist inhibited expression of these genes. Activation of ECs by complement depended on the autocrine action of IL-1α, because complement-mediated EC activation was inhibited by anti–IL-1α antibodies. Melittin and mastoparan, amphiphilic pore-forming peptides like the MAC, induced E-selectin through intermediary action of IL-1. Conclusions —These findings suggest that transmembrane pore-forming proteins, as a class of molecules, activate ECs through the autocrine effects of IL-1α.

Background —Cardiotrophin-1 (CT-1) is a potent hypertrophic factor discovered by coupling expression cloning in a mouse embryonic stem cell–based model of cardiogenesis. Methods and Results —The present study was designed to investigate the potential activation of atrial and ventricular CT-1 expression in pacing-induced experimental congestive heart failure (CHF) and its relationship to left ventricular hypertrophy by the method of Northern blot analysis and immunohistochemistry. We used a canine model of pacing-induced experimental CHF based on hemodynamic and neurohumoral characteristics that closely mimic human dilated cardiomyopathy. Northern blot analysis demonstrated that CT-1 gene expression was present in normal atrium and ventricle and was increased in CHF hearts. There was a positive correlation between ventricular CT-1 mRNA and left ventricular mass index. Immunohistochemistry revealed positive immunostaining in the atrial and ventricular cardiomyocytes from both normal and CHF hearts. CT-1 immunoreactivity was more intense in the atrium and ventricle from CHF hearts than in normal hearts. Conclusions —The present study demonstrates that both atrium and ventricle synthesize CT-1 and that cardiac production of CT-1 is augmented in a canine model of experimental CHF. This study also demonstrates that ventricular CT-1 mRNA correlates with left ventricular hypertrophy, suggesting that CT-1 plays an important role in the structural remodeling that characterizes CHF.

Background —Use of mortality as an end point in randomized trials of reperfusion therapy requires increasingly large sample sizes to test advances compared with existing therapy, which is already highly effective. There has been a growing interest in infarct size measurements by 99m Tc-sestamibi SPECT (single photon emission computed tomographic) imaging as a surrogate end point. Methods and Results —We reviewed the reports published in English regarding infarct size measurements by 99m Tc-sestamibi. Four separate lines of published evidence support the validity of SPECT imaging with 99m Tc-sestamibi for determination of infarct size. This end point has been used in a total of 7 randomized trials—1 single center and 6 multicenter. The end point compares favorably with left ventricular function and infarct size measurements with the use of other radiopharmaceuticals. The most important limitation of this approach is the absence thus far of a randomized trial that has shown a corresponding decrease in mortality in association with a therapy that reduces infarct size. Conclusions —SPECT imaging with 99m Tc-sestamibi is the best available measurement tool for infarct size. It has already served as an end point in early pilot studies to evaluate potential efficacy and in dose-ranging studies. It has the potential to serve as a surrogate end point to uncover advantages of new therapies that may be equivalent to existing therapies with respect to early mortality.

Background—This study compared the efficacy of ischemic preconditioning (IPC) and sodium-hydrogen exchanger (NHE)-1 inhibition to reduce infarct size (IS) induced by a 90-minute ischemic insult and examined the interaction between NHE-1 inhibition and IPC.Methods and Results—In a canine infarct model, either IPC, produced by 1 or four 5-minute coronary artery occlusions, or the specific NHE-1 inhibitor BIIB 513, 0.75 or 3.0 mg/kg, was administered 15 minutes before either a 60- or 90-minute coronary artery occlusion followed by 3 hours of reperfusion. IS was determined by TTC staining and expressed as a percentage of the area at risk (IS/AAR). Although both IPC and BIIB 513 at 0.75 mg/kg produced comparable and significant reductions in IS/AAR in the 60-minute occlusion model, insignificant reductions in IS/AAR were observed in the 90-minute occlusion model. However, BIIB 513 at 3.0 mg/kg markedly reduced IS in both models (P<0.05). Next, to examine the interaction between NHE-1 blockade and IPC, BIIB 0.75 mg/kg was administered either before IPC or during the washout phase of IPC before 90 minutes of coronary artery occlusion. Both combinations resulted in a greater-than-additive reduction in IS/AAR (P<0.05).Conclusions—These data demonstrate that although IPC and NHE-1 inhibition provide comparable protection against 60 minutes of myocardial ischemia, NHE-1 inhibition is more efficacious than IPC at protecting against a 90-minute ischemic insult. Furthermore, the combination of NHE-1 inhibition and IPC produces a greater-than-additive reduction in IS/AAR, suggesting either that NHE activity limits the efficacy of IPC or that different mechanisms are involved in the cardioprotective effect of IPC and NHE-1 inhibition.

Background—Neutral endopeptidase 24.11 (NEP) is a metalloprotease that is localized in the greatest abundance in the kidney and degrades natriuretic peptides, such as atrial natriuretic peptide (ANP). Mild congestive heart failure (CHF) is characterized by increases in circulating ANP without activation of the renin-angiotensin-aldosterone system (RAAS) or sodium retention. In contrast, severe CHF is characterized by sodium retention and coactivation of both ANP and the RAAS.Methods and Results—We defined the acute cardiorenal actions of the NEP inhibitor candoxatrilat (8 μg · kg−1· min−1) in 4 groups of anesthetized dogs (normal, n=8; mild CHF, n=6; severe CHF, n=5; and severe CHF with chronic AT1receptor antagonism, n=5). Mild CHF was produced by rapid ventricular pacing at 180 bpm for 10 days and severe CHF at 245 bpm for 10 days. In mild CHF, urinary sodium excretion and glomerular filtration rate were greatest in response to acute NEP inhibition compared with the response in either control animals or those with severe CHF. Furthermore, an increase in glomerular filtration rate was observed only in mild CHF in association with increases in renal blood flow and decreases in renal vascular resistance and distal tubular sodium reabsorption. Urinary ANP and cGMP excretion, markers for renal biological actions of ANP, were greatest in mild CHF. The renal actions observed in mild CHF were attenuated in severe CHF and not restored by chronic AT1receptor antagonism.Conclusions—The results of the present study demonstrate that acute NEP inhibition in mild CHF results in marked increases in renal hemodynamics and sodium excretion that exceed that observed in control animals and severe CHF. These studies underscore the potential therapeutic role for NEP inhibition to enhance renal function in mild CHF, an important phase of CHF that is marked by selective activation of endogenous ANP in the absence of an activated RAAS.

Background —Quantitative measures of myocardial perfusion defect severity from acute 99m Tc-sestamibi tomographic images (nadir) have correlated closely with collateral and residual antegrade blood flow during acute myocardial infarction. The purpose of this study was to determine whether a viability threshold could be identified from this measure in patients with acute myocardial infarction treated in a homogeneous manner with successful reperfusion therapy. Methods and Results —The study group consisted of 61 patients with acute myocardial infarction with a risk area of >6% LV treated with primary angioplasty between 120 and 240 minutes after symptom onset. All patients were injected with 20 to 30 mCi of 99m Tc-sestamibi before primary angioplasty and imaged after the procedure. Acute myocardium at risk (MAR) and subsequent infarct size (IS) were quantified by a threshold program. Severity (nadir) from the acute image was the lowest ratio of minimal/maximum counts from 5 short-axis slices. Infarct location was anterior in 22 and inferior in 39 patients. MAR was 33±15% LV and IS was 13±15% LV: 23 patients had no infarction despite MAR similar to those with infarction. Receiver-operator characteristic curve analysis identified a nadir value of 0.26 as providing the best separation of patients with and without infarction (sensitivity, 74%; specificity, 74%). This nadir threshold varied by infarct location: anterior defect, 0.21; inferior defect, 0.31. The sensitivity and specificity for absent infarction for these values were anterior, 69% and 67%, and inferior, 88% and 84%, respectively. Conclusions —In a time frame in which the presence of residual blood flow is important, the severity of the acute 99m Tc-sestamibi defect can be used to predict whether infarction will develop despite successful reperfusion.

Background —The appropriate management of patients with intermediate-risk Duke treadmill scores is not established. The purpose of this study was to determine the long-term risk of subsequent cardiovascular events in patients with an intermediate-risk treadmill score who do not have myocardial perfusion defects on radionuclide imaging. Methods and Results —The existing databases of the nuclear cardiology laboratories of 4 academic institutions were searched retrospectively. A total of 4649 patients were identified who had intermediate-risk Duke treadmill scores (−10 to 4), normal or near-normal exercise single photon-emission computed tomographic myocardial perfusion images using either thallium-201 or technetium-99m sestamibi, and no previous coronary revascularization. Follow-up was 95% complete. Cardiovascular survival was 99.8% at 1 year, 99.0% at 5 years, and 98.5% at 7 years. Cardiac survival free of myocardial infarction was similarly high at 96.6% at 7 years. Cardiac survival free of myocardial infarction or revascularization was 87.1% at 7 years. Near-normal scans and cardiac enlargement were independent predictors of time to cardiac death. Seven-year cardiac survival was still high at 97.0% in the 357 patients with near-normal scans and normal cardiac size and somewhat lower, at 89.0%, in the 167 patients with cardiac enlargement. Conclusions —Patients with an intermediate-risk treadmill score but with normal or near-normal exercise myocardial perfusion images and normal cardiac sizes are at low risk for subsequent cardiac death and can be safely managed medically until their symptoms warrant revascularization. The appropriate management of patients with cardiac enlargement will remain a matter of clinical judgment.

Background —Monocytes are constitutively activated in unstable angina (UA), resulting in the production of IL-6 and the upregulation of acute phase proteins. Underlying mechanisms are not understood. To explore whether the production of the potent monocyte activator IFN-γ is altered in UA, we compared cytokine production by T lymphocytes in patients with UA (Braunwald’s class IIIB) and with stable angina (SA). Methods and Results —Peripheral blood lymphocytes were collected at the time of hospitalization and after 2 and 12 weeks. Cytokine-producing CD4 + and CD8 + T cells were quantified by 3-color flow cytometry after stimulation with phorbol myristate acetate and ionomycin. UA was associated with an increased number of CD4 + and CD8 + T cells producing IFN-γ, whereas patients with SA had higher frequencies of IL-2 + and IL-4 + CD4 + T cells. Expansion of the IFN-γ + T-cell population in UA persisted for at least 3 months. Increased production of IFN-γ in UA could be attributed to the expansion of an unusual subset of T cells, CD4 + CD28 null T cells. Conclusions —Patients with UA are characterized by a perturbation of the functional T-cell repertoire with a bias toward IFN-γ production, suggesting that monocyte activation and acute phase responses are consequences of T-cell activation. IFN-γ is produced by CD4 + CD28 null T cells, which are expanded in UA and distinctly low in SA and controls. The emergence of CD4 + CD28 null T cells may result from persistent antigenic stimulation.

Background —Time to treatment with thrombolytic therapy is a critical determinant of mortality in acute myocardial infarction. Little is known about the relationship between the time to treatment with direct coronary angioplasty and clinical outcome. The objectives of this study were to determine both the time required to perform direct coronary angioplasty in the Global Use of Strategies to Open Occluded Arteries in Acute Coronary Syndromes (GUSTO-IIb) trial and its relationship to clinical outcome. Methods and Results —Patients randomized to direct coronary angioplasty (n=565) were divided into groups based on the time between study enrollment and first balloon inflation. Patients randomized to angioplasty who did not undergo the procedure were also analyzed. The median time from study enrollment to first balloon inflation was 76 minutes; 19% of patients assigned to angioplasty did not undergo an angioplasty procedure. The 30-day mortality rate of patients who underwent balloon inflation ≤60 minutes after study enrollment was 1.0%; 61 to 75 minutes after enrollment, 3.7%; 76 to 90 minutes after enrollment, 4.0%; and ≥91 minutes after enrollment, 6.4%. The mortality rate of patients assigned to angioplasty who never underwent the procedure was 14.1% ( P =0.001). Logistic regression analysis revealed that the time from enrollment to first balloon inflation was a significant predictor of mortality within 30 days; after adjustment for differences in baseline characteristics, the odds of death increased 1.6 times ( P =0.008) for a movement from each time interval to the next. Conclusions —The time to treatment with direct PTCA, as with thrombolytic therapy, is a critical determinant of mortality.