Jordan T. Shin

Sildenafil Improves Exercise Hemodynamics and Oxygen Uptake in Patients With Systolic Heart Failure

Background— Heart failure (HF) is frequently associated with dysregulation of nitric oxide–mediated pulmonary vascular tone. Sildenafil, a type 5 phosphodiesterase inhibitor, lowers pulmonary vascular resistance in pulmonary hypertension by augmenting intracellular levels of the nitric oxide second messenger, cyclic GMP. We tested the hypothesis that a single oral dose of sildenafil (50 mg) would improve exercise capacity and exercise hemodynamics in patients with chronic systolic HF through pulmonary vasodilation. Methods and Results— Thirteen patients with New York Heart Association class III HF underwent assessment of right heart hemodynamics, gas exchange, and first-pass radionuclide ventriculography at rest and with cycle ergometry before and 60 minutes after administration of 50 mg of oral sildenafil. Sildenafil reduced resting pulmonary arterial pressure, systemic vascular resistance, and pulmonary vascular resistance, and increased resting and exercise cardiac index (P<0.05 for all) without altering mean arterial pressure, heart rate, or pulmonary capillary wedge pressure. Sildenafil reduced exercise pulmonary arterial pressure, pulmonary vascular resistance, and pulmonary vascular resistance/systemic vascular resistance ratio, which indicates a selective pulmonary vasodilator effect with exercise. Peak &OV0312;o2 increased (15±9%) and ventilatory response to CO2 output (&OV0312;e/&OV0312;co2 slope) decreased (16±5%) after sildenafil treatment. Improvements in right heart hemodynamics and exercise capacity were confined to patients with secondary pulmonary hypertension (rest pulmonary arterial pressure >25 mm Hg). Conclusions— The present study shows that in patients with systolic HF, type 5 phosphodiesterase inhibition with sildenafil improves peak &OV0312;o2, reduces &OV0312;e/&OV0312;co2 slope, and acts as a selective pulmonary vasodilator during rest and exercise in patients with HF and pulmonary hypertension.

Use of amino-terminal pro-B-type natriuretic peptide to guide outpatient therapy of patients with chronic left ventricular systolic dysfunction.

OBJECTIVES The aim of this study was to evaluate whether chronic heart failure (HF) therapy guided by concentrations of amino-terminal pro-B-type natriuretic peptide (NT-proBNP) is superior to standard of care (SOC) management. BACKGROUND It is unclear whether standard HF treatment plus a goal of reducing NT-proBNP concentrations improves outcomes compared with standard management alone. METHODS In a prospective single-center trial, 151 subjects with HF due to left ventricular (LV) systolic dysfunction were randomized to receive either standard HF care plus a goal to reduce NT-proBNP concentrations ≤1,000 pg/ml or SOC management. The primary endpoint was total cardiovascular events between groups compared using generalized estimating equations. Secondary endpoints included effects of NT-proBNP-guided care on patient quality of life as well as cardiac structure and function, assessed with echocardiography. RESULTS Through a mean follow-up period of 10 ± 3 months, a significant reduction in the primary endpoint of total cardiovascular events was seen in the NT-proBNP arm compared with SOC (58 events vs. 100 events, p = 0.009; logistic odds for events 0.44, p = 0.02); Kaplan-Meier curves demonstrated significant differences in time to first event, favoring NT-proBNP-guided care (p = 0.03). No age interaction was found, with elderly patients benefitting similarly from NT-proBNP-guided care as younger subjects. Compared with SOC, NT-proBNP-guided patients had greater improvements in quality of life, demonstrated greater relative improvements in LV ejection fraction, and had more significant improvements in both LV end-systolic and -diastolic volume indexes. CONCLUSIONS In patients with HF due to LV systolic dysfunction, NT-proBNP-guided therapy was superior to SOC, with reduced event rates, improved quality of life, and favorable effects on cardiac remodeling. (Use of NT-proBNP Testing to Guide Heart Failure Therapy in the Outpatient Setting; NCT00351390).

Locus for Atrial Fibrillation Maps to Chromosome 6q14–16

Background—Atrial fibrillation (AF), the most common clinical arrhythmia, is a major cause of morbidity and mortality. Although AF is often associated with other cardiovascular conditions, many patients present without an obvious etiology. Inherited forms of AF exist, but the causative gene has been defined only in a single family. We have identified a large family (family FAF‐1) in which AF segregates as a Mendelian trait. Methods and Results—Thirty‐four family members were evaluated by 12‐lead ECG, echocardiogram, 24‐hour Holter monitoring, and laboratory studies. Individuals with electrocardiographically documented AF were defined as affected. Subjects were considered unaffected if they were >60 years of age, had no personal history of AF, and had no offspring with a history of AF. DNA was extracted and genotypic analyses were performed using polymorphic microsatellite markers. Evidence of linkage was obtained on chromosome 6, with a peak 2‐point logarithm of the odds (LOD) score of 3.63 (&thetas;=0) at the marker D6S1021. A maximal multipoint LOD score of 4.9 was obtained between D6S286 and D6S1021, indicating odds of ≈100 000:1 in favor of this interval as the location of the gene defect responsible for AF in this family. The LOD scores were robust to changes in penetrance and allele frequency. Haplotype analyses further supported this minimal genetic interval. Conclusion—We have mapped a novel locus for AF to chromosome 6q14‐16. The identification of the causative gene in this interval will be an important step in understanding the fundamental mechanisms of AF. (Circulation. 2003;107: 2880‐2883.)

Mutant Desmocollin-2 Causes Arrhythmogenic Right Ventricular Cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetically heterogeneous heart-muscle disorder characterized by progressive fibrofatty replacement of right ventricular myocardium and an increased risk of sudden cardiac death. Mutations in desmosomal proteins that cause ARVC have been previously described; therefore, we investigated 88 unrelated patients with the disorder for mutations in human desmosomal cadherin desmocollin-2 (DSC2). We identified a heterozygous splice-acceptor-site mutation in intron 5 (c.631-2A-->G) of the DSC2 gene, which led to the use of a cryptic splice-acceptor site and the creation of a downstream premature termination codon. Quantitative analysis of cardiac DSC2 expression in patient specimens revealed a marked reduction in the abundance of the mutant transcript. Morpholino knockdown in zebrafish embryos revealed a requirement for dsc2 in the establishment of the normal myocardial structure and function, with reduced desmosomal plaque area, loss of the desmosome extracellular electron-dense midlines, and associated myocardial contractility defects. These data identify DSC2 mutations as a cause of ARVC in humans and demonstrate that physiologic levels of DSC2 are crucial for normal cardiac desmosome formation, early cardiac morphogenesis, and cardiac function.

Mutation in the transcriptional coactivator EYA4 causes dilated cardiomyopathy and sensorineural hearing loss

We identified a human mutation that causes dilated cardiomyopathy and heart failure preceded by sensorineural hearing loss (SNHL). Unlike previously described mutations causing dilated cardiomyopathy that affect structural proteins, this mutation deletes 4,846 bp of the human transcriptional coactivator gene EYA4. To elucidate the roles of eya4 in heart function, we studied zebrafish embryos injected with antisense morpholino oligonucleotides. Attenuated eya4 transcript levels produced morphologic and hemodynamic features of heart failure. To determine why previously described mutated EYA4 alleles cause SNHL without heart disease, we examined biochemical interactions of mutant Eya4 peptides. Eya4 peptides associated with SNHL, but not the shortened 193–amino acid peptide associated with dilated cardiomyopathy and SNHL, bound wild-type Eya4 and associated with Six proteins. These data define unrecognized and crucial roles for Eya4-Six–mediated transcriptional regulation in normal heart function.

Cardiac Transplantation Followed by Dose-intensive Melphalan and Autologous Stem-cell Transplantation for Light Chain Amyloidosis and Heart Failure

Background. Patients with light chain (AL) amyloidosis who present with severe heart failure due to cardiac involvement rarely survive more than 6 months. Survival after cardiac transplantation is markedly reduced due to the progression of amyloidosis. Autologous stem-cell transplantation (ASCT) has become a common therapy for AL amyloidosis, but there is an exceedingly high treatment-related mortality in patients with heart failure. Methods. We developed a treatment strategy of cardiac transplant followed by ASCT. Twenty-six patients were evaluated, and of 18 eligible patients, nine patients underwent cardiac transplantation. Eight of these patients subsequently received an ASCT. Results. Six of seven evaluable patients achieved a complete hematologic remission, and one achieved a partial remission. At a median follow-up of 56 months from cardiac transplant, five of seven patients are alive without recurrent amyloidosis. Their survival is comparable with 17,389 patients who received heart transplants for nonamyloid heart disease: 64% in nonamyloid vs. 60% in amyloid patients at 7 years (P=0.83). Seven of eight transplanted patients have had no evidence of amyloid in their cardiac allograft. Conclusions. This demonstrates that cardiac transplantation followed by ASCT is feasible in selected patients with AL amyloidosis and heart failure, and that such a strategy may lead to improved overall survival.

The tuning of a splash

A water drop falling into a shallow pool of water can give rise to a splash that ejects droplet fragments high into the air. The height reached by the highest‐flying ejected droplet is greatest when the depth of the target liquid is equal to the radius of the hemispherical crater formed by the impact of the incident drop. This phenomenon, referred to here as the tuning of a splash, is still observed when liquids of very different viscosity and surface tension are substituted for water, but a thin sponge layer cemented over the floor of the pan all but destroys the tuning behavior. Cine images reveal a possible explanation for the tuning phenomenon based on a delay of the upward retraction of the collapsing crater.

High-resolution cardiovascular function confirms functional orthology of myocardial contractility pathways in zebrafish

Phenotype-driven screens in larval zebrafish have transformed our understanding of the molecular basis of cardiovascular development. Screens to define the genetic determinants of physiological phenotypes have been slow to materialize as a result of the limited number of validated in vivo assays with relevant dynamic range. To enable rigorous assessment of cardiovascular physiology in living zebrafish embryos, we developed a suite of software tools for the analysis of high-speed video microscopic images and validated these, using established cardiomyopathy models in zebrafish as well as modulation of the nitric oxide (NO) pathway. Quantitative analysis in wild-type fish exposed to NO or in a zebrafish model of dilated cardiomyopathy demonstrated that these tools detect significant differences in ventricular chamber size, ventricular performance, and aortic flow velocity in zebrafish embryos across a large dynamic range. These methods also were able to establish the effects of the classic pharmacological agents isoproterenol, ouabain, and verapamil on cardiovascular physiology in zebrafish embryos. Sequence conservation between zebrafish and mammals of key amino acids in the pharmacological targets of these agents correlated with the functional orthology of the physiological response. These data provide evidence that the quantitative evaluation of subtle physiological differences in zebrafish can be accomplished at a resolution and with a dynamic range comparable to those achieved in mammals and provides a mechanism for genetic and small-molecule dissection of functional pathways in this model organism.

Visnagin protects against doxorubicin-induced cardiomyopathy through modulation of mitochondrial malate dehydrogenase

A drug that targets the mitochondrial enzyme malate dehydrogenase protects against cardiotoxicity from the anticancer drug doxorubicin. Taming the Red Devil The cancer chemotherapy drug doxorubicin saves lives but its propensity to also inflict damage on the heart has earned it the nickname of the Red Devil. Liu et al. have now identified a compound that can prevent this drug-induced heart damage while leaving its cancer killing qualities intact. This agent, visnatin, was found among 3000 tested on a versatile piscine model, the zebrafish. After doxorubicin treatment, zebrafish hearts too suffer damage and visnagin protected them from injury. These salutary effects of visnagin were also apparent in mice, where it acts through mitochondrial malate dehydrogenase, a key metabolic enzyme. This or similar drugs may prove to be a valuable companion for doxorubicin, allowing it to acquire a less fiendish nickname. Doxorubicin is a highly effective anticancer chemotherapy agent, but its use is limited by its cardiotoxicity. To develop a drug that prevents this toxicity, we established a doxorubicin-induced cardiomyopathy model in zebrafish that recapitulates the cardiomyocyte apoptosis and contractility decline observed in patients. Using this model, we screened 3000 compounds and found that visnagin (VIS) and diphenylurea (DPU) rescue the cardiac performance and circulatory defects caused by doxorubicin in zebrafish. VIS and DPU reduced doxorubicin-induced apoptosis in cultured cardiomyocytes and in vivo in zebrafish and mouse hearts. VIS treatment improved cardiac contractility in doxorubicin-treated mice. Further, VIS and DPU did not reduce the chemotherapeutic efficacy of doxorubicin in several cultured tumor lines or in zebrafish and mouse xenograft models. Using affinity chromatography, we found that VIS binds to mitochondrial malate dehydrogenase (MDH2), a key enzyme in the tricarboxylic acid cycle. As with VIS, treatment with the MDH2 inhibitors mebendazole, thyroxine, and iodine prevented doxorubicin cardiotoxicity, as did treatment with malate itself, suggesting that modulation of MDH2 activity is responsible for VIS’ cardioprotective effects. Thus, VIS and DPU are potent cardioprotective compounds, and MDH2 is a previously undescribed, druggable target for doxorubicin-induced cardiomyopathy.

Differential activation of natriuretic peptide receptors modulates cardiomyocyte proliferation during development

Organ development is a highly regulated process involving the coordinated proliferation and differentiation of diverse cellular populations. The pathways regulating cell proliferation and their effects on organ growth are complex and for many organs incompletely understood. In all vertebrate species, the cardiac natriuretic peptides (ANP and BNP) are produced by cardiomyocytes in the developing heart. However, their role during cardiogenesis is not defined. Using the embryonic zebrafish and neonatal mammalian cardiomyocytes we explored the natriuretic peptide signaling network during myocardial development. We observed that the cardiac natriuretic peptides ANP and BNP and the guanylate cyclase-linked natriuretic peptide receptors Npr1 and Npr2 are functionally redundant during early cardiovascular development. In addition, we demonstrate that low levels of the natriuretic peptides preferentially activate Npr3, a receptor with Gi activator sequences, and increase cardiomyocyte proliferation through inhibition of adenylate cyclase. Conversely, high concentrations of natriuretic peptides reduce cardiomyocyte proliferation through activation of the particulate guanylate cyclase-linked natriuretic peptide receptors Npr1 and Npr2, and activation of protein kinase G. These data link the cardiac natriuretic peptides in a complex hierarchy modulating cardiomyocyte numbers during development through opposing effects on cardiomyocyte proliferation mediated through distinct cyclic nucleotide signaling pathways.