The therapeutic effect of natriuretic peptides in heart failure; differential regulation of endothelial and inducible nitric oxide synthases

Bioavailability and molecular activities of anthocyanins as modulators of endothelial function

Anthocyanins (AC) are water-soluble natural pigments found in various parts of higher plants. Despite their limited oral bioavailability and very low post-absorption plasma concentrations, the dietary consumption of these pigments has been proposed to be associated with a significant protection against several human pathological conditions, including cardiovascular diseases. Many studies highlighted that some health benefits of AC localize in particular at endothelium level, contributing to vascular homeostasis and also to the control of angiogenesis, inflammation, and platelet aggregation. This review reports and comments on the large existing literature addressing the molecular mechanisms that, beyond the antioxidant properties, may have a significant role in the effects of AC and AC-rich foods on vessel endothelium. Among these, AC have been reported to prevent peroxynitrite-mediated endothelial dysfunction in endothelial cells (ECs), thanks to their capability to modulate the expression and activity of several enzymes involved in NO metabolism. Furthermore, evidence indicates that AC can prevent the expression of adhesion molecules and the adhesion of monocytes to ECs challenged by pro-inflammatory agents. Overall, the activity of AC could be associated with the ability to elicit cell adaptive responses involving the transcription factor Nrf2 by affecting the "nucleophilic tone" of the organism. This review confirms the importance of specific nutritional molecules for human health and suggests new avenues for nutrition-based interventions to reduce the risk of cardiovascular disease in the population.

Carperitide induces coronary vasodilation and limits infarct size in canine ischemic hearts: role of NO

Carperitide is effective for heart failure (HF) owing to its diuretic and vasodilatory effects. This recombinant peptide may also have direct cardioprotective effects because carperitide reduces the severity of heart failure and limits infarct size. Because coronary vasodilation is an important cardioprotective treatment modality, we investigated whether carperitide increased coronary blood flow (CBF) and improved myocardial metabolic and contractile dysfunction during ischemia in canine hearts. We also tested whether carperitide is directly responsible for limiting the infarct size. We infused carperitide at 0.025-0.2 μg kg(-1) min(-1) into the canine coronary artery. A minimum dose of 0.1 μg kg(-1) min(-1) was required to obtain maximal vasodilation. To test the effects of carperitide on ischemic hearts, we reduced perfusion pressure in the left anterior descending coronary artery such that CBF decreased to one-third of the baseline value. At 10 min after carperitide was infused at a dose of 0.1 μg kg(-1) min(-1), we observed increases in CBF, fractional shortening (FS) and pH levels in coronary venous blood without concomitant increases in cardiac nitric oxide (NO) levels; these changes were attenuated using either the atrial natriuretic peptide receptor antagonist HS-142-1 or the NO synthase inhibitor L(ω)-nitroarginine methyl ester (L-NAME). Cyclic guanosine monophosphate (GMP) levels in the coronary artery were elevated in response to carperitide that also limited the infarct size after 90 min of ischemia and subsequent reperfusion. Again, these effects were blunted by L-NAME. Carperitide increases CBF, reduces myocardial contractile and metabolic dysfunction and limits infarct size. In addition, NO is necessary for carperitide-induced vasodilation and cardioprotection in ischemic hearts.

Activation of SUR2B/Kir6.1 subtype of adenosine triphosphate-sensitive potassium channel improves pressure overload-induced cardiac remodeling via protecting endothelial function

We sought to explore new strategies targeting SUR2B/Kir6.1, a subtype of adenosine triphosphate (ATP)-sensitive potassium channels (KATP), against pressure overload-induced heart failure. The effects of natakalim, a SUR2B/Kir6.1 selective channel opener, on progression of cardiac remodeling were investigated. Pressure overload-induced heart failure was induced in Wistar rats by abdominal aortic banding. The effects of natakalim (1, 3, and 9 mg·kg⁻¹·d⁻¹ for 10 weeks) on myocardial hypertrophy and heart failure, cardiac histology, vasoactive compounds, and gene expression were assessed. Ten weeks after the onset of pressure overload, natakalim treatment potently inhibited cardiac hypertrophy and prevented heart failure. Natakalim remarkably inhibited the changes of left ventricular hemodynamic parameters and reversed the increase of heart mass index, left ventricular weight index, and lung weight index. Histological examination demonstrated that there was no significant hypertrophy or fibrosis in pressure-overloaded hearts of natakalim-treated rats. Ultrastructural examination of hearts revealed well-organized myofibrils with mitochondria grouped along the periphery of longitudinally oriented fibers in rats from the natakalim group. The content of serum nitric oxide and plasma prostacyclin was increased, whereas that of plasma endothelin-1 and cardiac tissue hydroxyproline and atrial and B-type natriuretic peptide messenger RNA was downregulated in natakalim-treated rats. Natakalim at 0.01-100 µM had no effects on isolated working hearts derived from Wistar rats; however, natakalim had endothelium-dependent vasodilatory effects on the isolated tail artery helical strips precontracted with norepinephrine. These results indicate that natakalim reduces heart failure caused by pressure overloading by activating the SUR2B/Kir6.1 KATP channel subtype and protecting against endothelial dysfunction.

Nesiritide acutely increases pulmonary and systemic levels of nitric oxide in patients with pulmonary hypertension

BACKGROUND

Pulmonary hypertension (PH) is characterized by decreased pulmonary vascular expression of nitric oxide (NOx), a vasodilator that increases levels of smooth muscle cyclic guanosine monophosphate (cGMP). This study investigated mechanisms by which the vasodilator B-type natriuretic peptide (BNP) affects the systemic and pulmonary vasculature in PH patients.

METHODS AND RESULTS

Twenty PH patients with mean pulmonary artery (PA) pressure > 25 mm Hg were enrolled. Ten had precapillary (pulmonary capillary wedge pressure [PCWP] < or = 15 mm Hg) and 10 had postcapillary (PCWP > 15 mm Hg) PH. Right heart catheterization was performed before and 30 minutes after intravenous nesiritide infusion. NOx and cGMP levels from the PA and systemic (AO) arteries were obtained before and after nesiritide infusion. The postcapillary PH patients demonstrated significantly reduced pulmonary vascular resistance after nesiritide; there was no change in the precapillary PH cohort. NOx levels increased significantly in both AO (P < .0001) and PA (P = .0093), as did cGMP levels (P < .0001). There was a higher increase in NOx levels from the pulmonary arteries in precapillary PH patients compared to postcapillary PH patients (P = .020).

CONCLUSION

In PH patients, nesiritide infusion significantly increases NOx levels, suggesting a novel mechanism for its vasodilatory effects. These responses may differ between pre- and postcapillary PH patients.

Inhibition of nitric oxide biosynthesis by anthocyanin fraction of blackberry extract

Anthocyanins are natural colorant belonging to the flavonoid family, widely distributed among flowers, fruits, and vegetables. Some flavonoids have been found to possess anticarcinogenic, cytotoxic, cytostatic, antioxidant, and anti-inflammatory properties. Since increased nitric oxide (NO) plays a role in inflammation, we have investigated whether the pharmacological activity of the anthocyanin fraction of a blackberry extract (cyanidin-3-O-glucoside representing about 88% of the total anthocyanin content) was due to the suppression of NO synthesis. The markedly increased production of nitrites by stimulation of J774 cells with lipopolysaccharide (LPS) for 24 h was concentration-dependently inhibited by the anthocyanin fraction (11, 22, 45, and 90 microg/ml) of the extract. Moreover, this inhibition was dependent on a dual mechanism, since the extract attenuated iNOS protein expression and decreased the iNOS activity in lungs from LPS-stimulated rats. Inhibition of iNOS protein expression appeared to be at the transcriptional level, since the extract and similarly cyanidin-3-O-glucoside (10, 20, 40, and 80 microg/ml, amounts corresponding to the concentrations present in the extract) decreased LPS-induced NF-kappaB activation, through inhibition of IkappaBalpha degradation, and reduced ERK-1/2 phosphorylation in a concentration-dependent manner. In conclusion, our study demonstrates that at least some part of the anti-inflammatory activity of blackberry extract is due to the suppression of NO production by cyanidin-3-O-glucoside, which is the main anthocyanin present in the extract. The mechanism of this inhibition seems to be due to an action on the expression/activity of the enzyme. In particular, the protein expression was inhibited through the attenuation of NF-kappaB and/or MAPK activation.

Vitamin E increases production of vasodilator prostanoids in human aortic endothelial cells through opposing effects on cyclooxygenase-2 and phospholipase A2

Impairment of endothelium-dependent vasodilation is associated with the initiation and development of atherosclerosis. Vasodilator prostanoids constitute a protective mechanism in maintaining normal vasomotor function. In the current study, we determined the effect of in vitro vitamin E supplementation at physiologically relevant concentrations (10-60 micromol/L) on the production of the vasodilator prostanoids prostaglandin I(2) (PGI(2); prostacyclin) and prostaglandin E(2)(PGE(2)) by human aortic endothelial cells (HAECs) as well as its underlying mechanism. Results showed that vitamin E dose dependently (10-40 micromol/L) increased the production of both prostanoids by HAECs. This was associated with a dose-dependent (10-40 micromol/L) upregulation of cytosolic phospholipase A(2) (cPLA(2)) expression and arachidonic acid release. In contrast, vitamin E dose dependently (10-60 micromol/L) inhibited cyclooxygenase (COX) activity but did not affect the expression of either COX-1 or COX-2, indicating that the effect of vitamin E on COX activity was post-translational. Thus, vitamin E had opposing effects on the 2 key enzymes in prostanoid biosynthesis; at the concentrations used in this study, this resulted in a net increase in the production of vasodilator prostanoids. The vitamin E-induced increase in PGI(2) and PGE(2) production may contribute to its suggested beneficial effect in preserving endothelial function.

Fluorescence imaging microscopy of cellular markers in ischemic vs non-ischemic cardiomyopathy after left ventricular unloading

BACKGROUND

The heart undergoes repair and initiates protective mechanisms via ventricular unloading. We examined the presence of 2 markers in pre-unloaded and post-unloaded human cardiac tissue that are important indicators of cardiac failure, tumor necrosis factor-alpha and inducible nitric oxide synthase. We also measured 2 nuclear transcription factors, NFkappaB50 and NFkappaB65, comparing quantities and localizations to determine if mechanical unloading reduced their presence, as these markers are also thought to be indicators of impending heart failure. Amounts and localizations in patients that had been diagnosed with either ischemic or non-ischemic cardiomyopathy were compared after mechanical unloading with a left ventricular assist device. To establish that unloading had been achieved, levels of atrial natriuretic protein were determined.

METHODS

Core biopsies were harvested at assist device implantation and removal. Fluorescence deconvolution microscopy image reconstructions of fluorescence probes were correlated with data obtained by western Blot and electrobility shift assays.

RESULTS

Statistically significant differences in localization and amounts of tumor necrosis factor and nitric oxide synthase were seen between pre- and post-assist device samples. Amounts of tumor necrosis factor and nitric oxide synthase in ischemic tissue were increased at the time of assist device removal, but decreased in dilated or idiomyopathic samples. Ventricular unloading resulted in reduced levels of natriuretic protein, with the greatest reduction being seen in ischemic tissue. Both NFkappaB50 and NFkappaB65 increased in ischemic tissue, but only NFkappaB50 in non-ischemic samples.

CONCLUSIONS

Changes in localization of the factors and altered levels of cytokine and nitric oxide synthase indicate that the heart switches to a "protective and repair" mode, and mechanical unloading allows this transition to occur. Observed changes were dependent on the etiology of the disease.

Putting the brakes on cardiac hypertrophy: exploiting the NO-cGMP counter-regulatory system

We know a great deal about the receptors and signaling pathways in cardiomyocytes that contribute to hypertrophic growth. Although drugs that target them have proven effective in substantially reducing left ventricular hypertrophy and associated mortality, cardiovascular disease remains the leading cause of death in the West. Another approach may rest with exploiting naturally occurring regulators of maladaptive cardiac hypertrophy that have been identified in the past few years. These endogenous negative regulators can be grouped, for the most part, into those constitutively active but whose activity is decreased by hypertrophic stimulation, and those with little or no baseline activity that are activated by hypertrophic stimulation. Spanning both groups are 4 systems that converge on cyclic guanosine 3', 5'-monophosphate (cGMP) generation, namely natriuretic peptides (ANP and BNP), kinins, nitric oxide (NO), and the angiotensin II type 2 receptor (AT2). Although holding promise as a means for restricting hypertrophy, each of these signaling molecules has certain limitations that need to be overcome. What follows is an overview of research over the past 2 years, much of it published in Hypertension, which has dealt with the antihypertrophic action of this particular group of endogenous signaling molecules. Understanding the function and regulation of the antihypertrophic NO-cGMP system offers the promise of novel therapeutic strategies for treating cardiac hypertrophy and heart failure.

UTP transactivates epidermal growth factor receptors and promotes cardiomyocyte hypertrophy despite inhibiting transcription of the hypertrophic marker gene, atrial natriuretic peptide

In neonatal rat ventricular myocytes, activation of receptors that couple to the G(q) family of heterotrimeric G proteins causes hypertrophic growth, together with expression of "hypertrophic marker" genes, such as atrial natriuretic peptide (ANP) and myosin light chain 2 (MLC2). As reported previously for other G(q)-coupled receptors, stimulation of alpha(1)-adrenergic receptors with phenylephrine (50 microM) caused phosphorylation of epidermal growth factor (EGF) receptors as well as activation of ERK1/2, cellular growth, and ANP transcription. These responses depended on EGF receptor activation. In marked contrast, stimulation of G(q)-coupled purinergic receptors with UTP caused EGF receptor phosphorylation, ERK1/2 activation, and cellular growth but minimal increases in ANP transcription. UTP inhibited phenylephrine-dependent transcription from ANP and MLC2 promoters but not transcription from myoglobin promoters or from AP-1 elements. Myocardin is a muscle-specific transcription enhancer that activates transcription from ANP and MLC2 promoters but not myoglobin promoters or AP-1 elements. UTP inhibited ANP and MLC2 responses to overexpressed myocardin but did not inhibit responses to c-Jun, GATA4, or serum response factor, all of which are active in nonmuscle cells. Thus, UTP inhibits transcriptional responses to phenylephrine only at cardiac-specific promoters, and this may involve the muscle-specific transcription enhancer, myocardin. These studies show that EGF receptor activation is necessary but not sufficient for ANP and MLC2 responses to activation of G(q)-coupled receptors in ventricular myocytes, because inhibitory mechanisms can oppose such stimulation. ANP is a compensatory and protective factor in cardiac hypertrophy, and mechanisms that reduce its generation need to be defined.