Expression of atrial natriuretic factor in the human ventricle is independent of chamber dilation

Detection of differentially methylated gene promoters in failing and nonfailing human left ventricle myocardium using computation analysis

Human dilated cardiomyopathy (DCM) is characterized by congestive heart failure and altered myocardial gene expression. Epigenetic changes, including DNA methylation, are implicated in the development of DCM but have not been studied extensively. Clinical human DCM and nonfailing control left ventricle samples were individually analyzed for DNA methylation and expressional changes. Expression microarrays were used to identify 393 overexpressed and 349 underexpressed genes in DCM (GEO accession number: GSE43435). Gene promoter microarrays were utilized for DNA methylation analysis, and the resulting data were analyzed by two different computational methods. In the first method, we utilized subtractive analysis of DNA methylation peak data to identify 158 gene promoters exhibiting DNA methylation changes that correlated with expression changes. In the second method, a two-stage approach combined a particle swarm optimization feature selection algorithm and a discriminant analysis via mixed integer programming classifier to identify differentially methylated gene promoters. This analysis identified 51 hypermethylated promoters and six hypomethylated promoters in DCM with 100% cross-validation accuracy in the group assignment. Generation of a composite list of genes identified by subtractive analysis and two-stage computation analysis revealed four genes that exhibited differential DNA methylation by both methods in addition to altered gene expression. Computationally identified genes (AURKB, BTNL9, CLDN5, and TK1) define a central set of differentially methylated gene promoters that are important in classifying DCM. These genes have no previously reported role in DCM. This study documents that rigorous computational analysis applied to microarray analysis of healthy and diseased human heart samples helps to define clinically relevant DNA methylation and expressional changes in DCM.

Novel natriuretic peptides: new compounds and new approaches

The natriuretic peptides (NPs) are a group of structurally similar yet genetically distinct peptides that have diverse actions in cardiovascular, renal, and endocrine homeostasis. Since the discovery of atrial natriuretic peptide in 1981, the diagnostic, prognostic, and therapeutic significance of NPs have been studied extensively in relation to heart failure. Indeed, it now is understood that a hallmark of heart failure is the activation of the cardiac endocrine system, in particular the natriuretic peptide family including atrial natriuretic peptide and B-type natriuretic peptide. Currently, the only approved therapeutic application for NPs is the intravenous treatment of acute decompensated heart failure. However, in recent years there has been considerable research aimed at creating novel NPs and administering them via novel routes. This review focuses on the novel NPs that have been created and on novel approaches for their administration.

Ventricular expression of atrial natriuretic peptide in chronic chagasic cardiomyopathy is not induced by myocarditis

BACKGROUND

The ventricles of the normal heart are virtually devoid of atrial natriuretic peptide (ANP). Although ANP occurs in ventricles submitted to elevated wall stress, it is not clear whether ANP expression is affected by myocarditis. We investigated the immunohistochemical expression of ANP in chronic chagasic cardiomyopathy, an inflammatory cardiomyopathy caused by infection with the protozoan Trypanosoma cruzi.

METHODS

Necropsy samples from the left and right ventricles of 16 patients exhibiting chronic chagasic cardiomyopathy were evaluated for myocarditis, fibrosis, T. cruzi parasites and ANP immunoreactivity. The diameters of 50 myocytes per sample were measured.

RESULTS

ANP was present in myocytes of the subendocardial region in 13/16 (81.3%) left and 10/16 (62.5%) right ventricular samples (P=0.25). Myocytes present in the inflammatory foci, near the infiltrating inflammatory cells but distant from the subendocardial region, did not express ANP. Trypanosoma cruzi parasites exhibited intense immunoreactivity for ANP. The mean myocyte diameter and the incidence of myocarditis, fibrosis, and T. cruzi parasites was similar between the left and right ventricular samples. No statistical differences were found between the ANP-positive and ANP-negative cases.

CONCLUSIONS

In chronic chagasic cardiomyopathy, both ventricles exhibit hypertrophy, fibrosis and ANP in the subendocardial region. The inflammatory infiltrate does not induce ANP expression in the myocytes. Regional stress but not myocarditis itself, is probably responsible for ventricular ANP expression in myocarditis.

The time course of natriuretic hormones as plasma markers of myocardial recovery in heart transplant candidates during ventricular assist device support reveals differences among device types

BACKGROUND

The natriuretic hormones ANP and BNP are expressed differently in the myocardium. Both hormones have compensatory diuretic activity during heart failure. Mechanical stretch of the myocardial walls induces the expression of these hormones. In failing human myocardium, both ANP and BNP are transcribed in the ventricular myocardium in high amounts. We measured the plasma concentrations of ANP and BNP in patients supported by various ventricular assist devices (VADs) at various times. We analyzed the time courses of ANP and BNP to determine (1) the time scale of their down-regulation as a marker of putative myocardial recovery, (2) their steady-state levels under VAD support and (3) differences caused by various VAD devices.

METHODS

We analyzed ANP and BNP using commercially available radioimmune assays. We analyzed the time courses of patients supported by Thoratec (THO) LVAD (n = 8), TCI Heartmate (TCI) (n = 6), Novacor (NOV) (n = 7), and Lionheart (LIO) (n = 3).

RESULTS

Patients supported with NOV and some patients with TCI showed down-regulation of BNP to a steady-state level at 30 to 50 days, following a single exponential decay. In contrast, patients supported by THO or LIO did not reveal a determined time course of the natriuretic hormones. Only a few patients reached normal plasma values during VAD support.

CONCLUSION

The time courses of ANP and BNP differ among VAD types because of construction and/or driving mode, which might be important when considering patients for weaning from VAD without heart transplant.

Expression of atrial and brain natriuretic peptides and their genes in hearts of patients with cardiac amyloidosis

OBJECTIVES

We investigated the expression of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) and their genes in the hearts of patients with cardiac amyloidosis and those with isolated atrial amyloidosis.

BACKGROUND

The expression of ANP and BNP is augmented in the ventricles of failing or hypertrophied hearts, or both. The expression of ANP and BNP in the ventricles of hearts with cardiac amyloidosis, which is hemodynamically similar to restrictive cardiomyopathy, is not yet known. ANP is the precursor protein of isolated atrial amyloid.

METHODS

We analyzed the immunohistocytochemical localizations of ANP and BNP as well as the expression of their mRNAs by in situ hybridization in the myocardium and measured the plasma levels of ANP and BNP in patients with cardiac amyloidosis.

RESULTS

Four of the five right and all six left ventricular endomyocardial biopsy specimens obtained from six patients with cardiac amyloidosis were immunohistochemically positive for both ANP and BNP; none of the biopsy specimens from eight normal subjects were positive for ANP or BNP. All four of the right atria obtained at operation showed positive immunoreactions for both peptides. Electron microscopy identified specific secretory granules in ventricular myocytes of the patients with cardiac amyloidosis, but not in ventricular myocytes from the normal control subjects. Double immunocytochemical analysis revealed the co-localization of ANP and BNP in the same granules and that isolated atrial amyloid fibrils were immunoreactive for ANP and BNP, whereas ventricular amyloid fibrils were negative for both peptides. Both ANP mRNA and BNP mRNA were expressed in the ventricles of the patients with cardiac amyloidosis but not in the normal ventricles. The autopsy study of four patients with cardiac amyloidosis revealed an almost transmural distribution of ANP and BNP, with predominance in the endocardial side. Plasma BNP levels in the patients were markedly elevated ([mean +/- SD] 1,165.1+/-561.2 pg/ml) compared with those in the control subjects (8.9+/-6.0 pg/ml, p < 0.05).

CONCLUSIONS

Expression of ANP and BNP and their genes was augmented in the ventricular myocytes of the patients with cardiac amyloidosis. Both regional mechanical stress by amyloid deposits and hemodynamic stress by diastolic dysfunction may be responsible for the expression of the peptides in patients with cardiac amyloidosis.

Functional explanation for increased atrial natriuretic peptide in systemic sclerosis

We related atrial natriuretic peptide (ANP) among 30 consecutive patients with systemic sclerosis (SScl) and 48 gender- and age-matched controls to the measurements of left ventricular (LV) function as evaluated by echocardiography and external pulse curves to determine possible causative factors for an increased level of plasma ANP. The patients had a markedly elevated plasma ANP level (239.4 +/- 59 vs. 178.2 +/- 36 pmol/l, p < 0.0005), which was not related to LV systolic function, heart rate, or blood pressure. Patients had LV hypertrophy and plasma ANP correlated directly to interventricular septal thickness (r = 0.41, p < 0.005), LV posterior wall thickness (r = 0.32, p < 0.01), and wall thickness to cavity dimension (r = 0.44, p < 0.0005), LV mass index (r = 0.40, p < 0.005). LV early filling properties were impaired, with reduction of atrial emptying index (p < 0.0005) and increased contribution of atrial contraction to LV filling. Plasma ANP correlated to atrial emptying index (r = 0.41, p < 0.0005) and to apex-cardiographic a wave (r = 0.28, p < 0.05). Plasma ANP was also related to left atrial dimension index (r = 0.27, p < 0.05), and was still related to atrial emptying index, but not to left atrial dimension, when considering the degree of LV hypertrophy in multivariate analysis. We conclude that ANP is elevated in patients with SScl. Reduced LV compliance, probably due to increased fibrosis, may cause changes in atrial pressure sufficient to stimulate ANP production without systolic dysfunction as a prerequisite.

Differential localization of atrial natriuretic peptide and skeletal alpha-actin messenger RNAs in left ventricular myocytes of patients with dilated cardiomyopathy

OBJECTIVES

This study was designed to determine whether atrial natriuretic peptide and skeletal alpha-actin messenger RNAs (mRNAs) are co-localized in ventricular myocytes of patients with dilated cardiomyopathy.

BACKGROUND

Atrial natriuretic peptide and skeletal alpha-actin are known as augmented genes with cardiac hypertrophy. However, the expression and localization of both genes in chronic failing heart remain unclear.

METHODS

Left ventricular biopsy specimens were obtained from 14 patients with dilated cardiomyopathy. Atrial natriuretic peptide and skeletal alpha-actin mRNAs were detected by in situ hybridization with specific sulfur-35 uridine triphosphate-labeled RNA probes in the serial sections.

RESULTS

Atrial natriuretic peptide mRNA was detected in 10 patients, and intense signals were localized in the myocytes located in the subendocardium and around the interstitial fibrous area. By contrast, skeletal alpha-actin mRNA was homogeneously detected in all myocytes in seven patients. By left ventriculography, patients with skeletal alpha-actin-positive findings had a lower ejection fraction (37.1 +/- 6.0%) than those with negative findings (46.3 +/- 5.8%, p < 0.05), but atrial natriuretic peptide mRNA expression was not related to left ventricular function.

CONCLUSIONS

These results indicate that the expression of atrial natriuretic peptide and skeletal alpha-actin mRNAs are not always co-localized in the left ventricle of patients with dilated cardiomyopathy and suggest that the mechanisms of the regulation of these two genes in the chronic failing heart are different.

Molecular forms of atrial natriuretic factor in normal and failing human myocardium

BACKGROUND

Atrial natriuretic factor (ANF) is produced by myocardial tissue, and the plasma ANF concentration is known to be elevated in congestive heart failure (CHF). Data from animal models indicate that myocardial concentrations of ANF are depleted in CHF, and this has given rise to the hypothesis that CHF is characterized by depletion of stored ANF. To date, the molecular forms of ANF and their concentrations in atrial and ventricular myocardium remain poorly characterized in the normal and the failing human heart.

METHODS AND RESULTS

We measured ANF concentrations in fresh tissue from failing human hearts explanted at the time of cardiac transplantation and from organ donors whose normal hearts could not be used for transplantation. We determined total ANF and alpha, beta, and gamma ANF concentrations in the right and left atrial appendages, atrial free walls, and ventricles. In normal hearts, ANF concentration in the atrial appendages was 40-fold higher than ANF in the rest of the atrial free wall and in the ventricles. In the failing hearts, atrial appendage ANF concentrations increased 5- to 10-fold, and atrial free wall ANF concentrations increased 200-fold. Analysis of molecular forms of ANF demonstrated significant increases in the gamma and beta forms in the left atrial appendage of failing hearts. alpha, beta, and gamma ANF forms were also significantly increased in right and left atrial free wall tissue from failing hearts. In addition, failing hearts were characterized by absolute and relative increases in the precursor form gamma ANF.

CONCLUSIONS

These data from fresh tissues suggest that cardiac ANF stores are not decreased in severe CHF in humans; rather, chronic CHF is characterized by marked increases in atrial ANF tissue concentrations, particularly the beta and gamma ANF forms. These findings are consistent with intracellular accumulation of precursor ANF forms in severe chronic human CHF.

Expression of A-, B-, and C-type natriuretic peptide genes in failing and developing human ventricles. Correlation with expression of the Ca(2+)-ATPase gene

Brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) are novel natriuretic peptides, originally isolated from porcine brain. Similar to atrial natriuretic peptide (ANP), BNP is also synthesized in and secreted from cardiocytes, but CNP is not expressed at significant levels in normal adult myocardium. Previous studies have indicated that the serum level and ventricular expression of the ANP gene were augmented in patients with heart failure. Recently, the serum level of BNP was also reported to increase in human heart failure. To examine whether or not the expression of these natriuretic peptides is regulated in ventricular myocardium in a concordant manner, we performed Northern blot analysis using total cellular RNA isolated from the diseased left ventricles of 30 cardiac transplant recipients with end-stage heart failure, seven ventricles from organ donors (control group), and two ventricles of artificially aborted 17- and 19-week-old fetuses. The levels of mRNAs encoding both BNP and ANP increased significantly (p less than 0.01) in the left ventricular myocardium from the patients with end-stage heart failure as compared with the control group. The levels of BNP mRNA correlated positively with those of ANP mRNA (r = 0.73, p less than 0.01) and negatively with those of sarcoplasmic reticulum Ca(2+)-ATPase mRNA (r = -0.66, p less than 0.01) in the left ventricular myocardium from the patients with heart failure. There was also a negative correlation between the levels of ANP and the sarcoplasmic reticulum Ca(2+)-ATPase mRNAs (r = -0.65, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Passive mechanical stretch releases atrial natriuretic peptide from rat ventricular myocardium

Ventricular hypertrophy is characterized by augmentation of synthesis, storage, and release of atrial natriuretic peptide (ANP) from ventricular tissue, but the physiological stimulus for ANP release from ventricles is not known. We determined the effect of graded, passive myocardial stretch on ANP release in isolated, arrested, perfused heart preparations after removal of the atria in 13-20-month-old Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). By this age, ANP gene expression was increased in the hypertrophic ventricular cells of SHR, as reflected by elevated levels of immunoreactive ANP and ANP mRNA and the increased ANP secretion (SHR, 93 +/- 14 pg/ml, n = 22; WKY rats, 22 +/- 2 pg/ml, n = 20; p less than 0.001) from perfused ventricles after removal of the atria. The release of ANP from ventricles was examined at two levels of left ventricular pressure by increasing the volume of the intraventricular balloon for 10 minutes. Stretching of the ventricles produced a rapid but transient increase in ANP secretion. As left ventricular pressure rose from 0 to 14 and 26 mm Hg in WKY rats and from 0 to 13 and 27 mm Hg in SHR, increases in ANP release into the perfusate of 1.4 +/- 0.1-fold and 1.5 +/- 0.2-fold (p less than 0.05) in WKY rats and 1.1 +/- 0.1-fold and 1.6 +/- 0.2-fold (p less than 0.05) in SHR, respectively, were observed. There was a highly significant correlation between the left ventricular pressure level and the maximal concentration of ANP in the perfusate during stretching (p less than 0.001, r = 0.59, n = 42), as well as between the maximal ANP concentrations in perfusate during stretching and the ventricular weight/body weight ratios of the corresponding animals (r = 0.38, p less than 0.05, n = 42). High performance liquid chromatographic analysis revealed that the ventricles both before and during stretch primarily released the processed, active, 28-amino acid ANP-like peptide into the perfusate. These results indicate that stretching is a direct stimulus for ventricular ANP release and show that ANP is also a ventricular hormone.