B-type natriuretic peptide exerts broad functional opposition to transforming growth factor-beta in primary human cardiac fibroblasts: fibrosis, myofibroblast conversion, proliferation, and inflammation

NPRA-mediated suppression of AngII-induced ROS production contribute to the antiproliferative effects of B-type natriuretic peptide in VSMC

Excessive proliferation of vascular smooth cells (VSMCs) plays a critical role in the pathogenesis of diverse vascular disorders, and inhibition of VSMCs proliferation has been proved to be beneficial to these diseases. In this study, we investigated the antiproliferative effect of B-type natriuretic peptide (BNP), a natriuretic peptide with potent antioxidant capacity, on rat aortic VSMCs, and the possible mechanisms involved. The results indicate that BNP potently inhibited AngiotensinII (AngII)-induced VSMCs proliferation, as evaluated by [(3)H]-thymidine incorporation assay. Consistently, BNP significantly decreased AngII-induced intracellular reactive oxygen species (ROS) and NAD(P)H oxidase activity. 8-Br-cGMP, a cGMP analog, mimicked these effects. To confirm its mechanism, siRNA of natriuretic peptide receptor-A(NRPA) strategy technology was used to block cGMP production in VSMCs, and siNPRA attenuated the inhibitory effects of BNP in VSMCs. Taken together, these results indicate that BNP was capable of inhibiting VSMCs proliferation by NPRA/cGMP pathway, which might be associated with the suppression of ROS production. These results might be related, at least partly, to the anti-oxidant property of BNP.

Molecular and physiological effects of nesiritide

BACKGROUND

Nesiritide (Natrecor, Janssen-Ortho Inc, Canada), or recombinant human B-type natriurtic peptide (BNP), is a molecule identical in structure to endogenous BNP-32. This peptide is secreted from cardiac myocytes in response to volume and pressure overload. While high levels of circulating BNP are measured by commercially available assays during acute decompensated heart failure (ADHF), the detection of alternate, potentially more active, but undermeasured forms of BNP needs to be considered.

AIM

The present review summarizes the molecular and physiological effects of nesiritide in the setting of hospitalized patients with ADHF. In particular, an overview of the molecular structure and circulating isoforms of BNP is given, followed by a discussion of the vasodilatory, renal, antagonistic neurohormonal, pulmonary, anti-inflammatory and cardiac remodelling effects of recombinant human BNP.

SUMMARY

Nesiritide has beneficial effects in the treatment of ADHF that go beyond the traditional goals of reducing pulmonary capillary wedge pressure, preload and afterload, and relieving symptoms of dyspnea. Therefore, the unique pharmacological profile of this medication provides an additional treatment option for Canadian patients with ADHF.

Genetic variation in the natriuretic peptide system and heart failure

Heart failure (HF) is a modern epidemic and is one of the few cardiovascular diseases which is increasing in prevalence. The growing importance of the Natriuretic Peptide (NP) system in HF is well recognized. Laboratory tests for B-type Natriuretic Peptide (BNP) have proven value as diagnostic and prognostic tools in HF and are now part of routine clinical care. Furthermore, recombinant atrial natriuretic peptide (ANP) (carperitide) and BNP (nesiritide) and are approved HF therapies in Japan and the US, respectively and additional natriuretic peptides (e.g., CNP, urodilatin, and designer NPs) are under investigation for use in HF. Common genetic sequence variants are increasingly being recognized as determinants of disease risk or drug response and may help explain a portion of the inter-individual variation in the human NP system. This review describes current knowledge of NP system genetic variation as it pertains to HF as well as ongoing studies and where the field is expected to progress in the near future. To briefly summarize, NP system genetic variants have been associated with alterations in gene expression, NP levels, and cardiovascular disease. The next step forward will include specific investigations into how this genetic variation can advance 'Personalized Medicine', such as whether they impact the utility of diagnostic BNP testing or effectiveness of therapeutic NP infusion. This is already in progress, with pharmacogenetic studies of nesiritide currently underway. We expect that within 5 years there should be a reasonable idea of whether NP system genetic variation will have important clinical implications.

The effects of brain natriuretic peptide on scar formation in incisional rat wounds

BACKGROUND

Brain natriuretic peptide (BNP) is a peptide that reduces scar formation in the heart by blocking transforming growth factor-beta (TGF-beta). Although TGF-beta is known to play a role in scar formation in the myocardium, little is known about the effects of BNP on cutaneous wound healing.

OBJECTIVES

The objective was to determine if the administration of BNP in healing cutaneous wounds reduces the amount of scarring.

METHODS

This was a laboratory investigation using 40 wild-strain rats. Three full-thickness 1-cm incisional wounds were created on each animal and randomized to intradermal BNP, saline, or no treatment. Wounds were excised at 3, 7, 14, 31, and 60 days and examined histologically for scar surface area and collagen architecture. Those wounds excised at 30 days were subjected to a measure of tensile strength and those excised at 60 days were evaluated prior to excision for cosmesis using a scar evaluation scale. The proportion of wounds healing without visually apparent scar was the main outcome. Groups were compared with Fisher's exact and Kruskal-Wallis tests.

RESULTS

Wounds treated with BNP were more likely to heal without an apparent scar when compared to those treated with saline or control (37.5% vs. 0%, p = 0.03). There were no between-group differences in the surface area of the scars or the collagen architecture. Incisional tensile strength was also similar across treatments.

CONCLUSIONS

Treatment of rat incisions with BNP reduced the number of visually apparent scars but did not affect the histologic appearance of the scars or the incisional tensile strength.

Dysregulation of microRNAs after myocardial infarction reveals a role of miR-29 in cardiac fibrosis

Acute myocardial infarction (MI) due to coronary artery occlusion is accompanied by a pathological remodeling response that includes hypertrophic cardiac growth and fibrosis, which impair cardiac contractility. Previously, we showed that cardiac hypertrophy and heart failure are accompanied by characteristic changes in the expression of a collection of specific microRNAs (miRNAs), which act as negative regulators of gene expression. Here, we show that MI in mice and humans also results in the dysregulation of specific miRNAs, which are similar to but distinct from those involved in hypertrophy and heart failure. Among the MI-regulated miRNAs are members of the miR-29 family, which are down-regulated in the region of the heart adjacent to the infarct. The miR-29 family targets a cadre of mRNAs that encode proteins involved in fibrosis, including multiple collagens, fibrillins, and elastin. Thus, down-regulation of miR-29 would be predicted to derepress the expression of these mRNAs and enhance the fibrotic response. Indeed, down-regulation of miR-29 with anti-miRs in vitro and in vivo induces the expression of collagens, whereas over-expression of miR-29 in fibroblasts reduces collagen expression. We conclude that miR-29 acts as a regulator of cardiac fibrosis and represents a potential therapeutic target for tissue fibrosis in general.

Natriuretic peptides: an update on bioactivity, potential therapeutic use, and implication in cardiovascular diseases

The natriuretic peptide system includes three known peptides: atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP). They contribute to the regulation of cardiovascular homeostasis through diuretic, natriuretic, and vasodilatory properties. Among them, ANP has received particular attention because of its effects on blood pressure regulation and cardiac function. Although the potential for its therapeutic application in the treatment of hypertension and heart failure has been evaluated in several experimental and clinical investigations, no pharmacological approach directly targeted at modulation of ANP levels has ever reached the stage of being incorporated into clinical practice. Recently, ANP has also received attention as being a possible cardiovascular risk factor, particularly in the context of hypertension, stroke, obesity, and metabolic syndrome. Abnormalities in either peptide levels or peptide structure are thought to underlie its implied role in mediating cardiovascular diseases. Meanwhile, BNP has emerged as a relevant marker of left ventricular (LV) dysfunction and as a useful predictor of future outcome in patients with heart failure. This review deals with the major relevant findings related to the cardiovascular and metabolic effects of natriuretic peptides, to their potential therapeutic use, and to their role in mediating cardiovascular diseases.

Inhibition of the TGF-beta receptor I kinase promotes hematopoiesis in MDS

MDS is characterized by ineffective hematopoiesis that leads to peripheral cytopenias. Development of effective treatments has been impeded by limited insight into pathogenic pathways governing dysplastic growth of hematopoietic progenitors. We demonstrate that smad2, a downstream mediator of transforming growth factor-beta (TGF-beta) receptor I kinase (TBRI) activation, is constitutively activated in MDS bone marrow (BM) precursors and is overexpressed in gene expression profiles of MDS CD34(+) cells, providing direct evidence of overactivation of TGF-beta pathway in this disease. Suppression of the TGF-beta signaling by lentiviral shRNA-mediated down-regulation of TBRI leads to in vitro enhancement of hematopoiesis in MDS progenitors. Pharmacologic inhibition of TBRI (alk5) kinase by a small molecule inhibitor, SD-208, inhibits smad2 activation in hematopoietic progenitors, suppresses TGF-beta-mediated gene activation in BM stromal cells, and reverses TGF-beta-mediated cell-cycle arrest in BM CD34(+) cells. Furthermore, SD-208 treatment alleviates anemia and stimulates hematopoiesis in vivo in a novel murine model of bone marrow failure generated by constitutive hepatic expression of TGF-beta1. Moreover, in vitro pharmacologic inhibition of TBRI kinase leads to enhancement of hematopoiesis in varied morphologic MDS subtypes. These data directly implicate TGF-beta signaling in the pathobiology of ineffective hematopoiesis and identify TBRI as a potential therapeutic target in low-risk MDS.

Significance of plasma levels of N-terminal Pro-B-type natriuretic peptide on left ventricular remodeling in non-obstructive hypertrophic cardiomyopathy attributable to the Asp175Asn mutation in the alpha-tropomyosin gene

Hypertrophic cardiomyopathy (HC) is an inherited heart disease characterized by left ventricular (LV) remodeling. The present study was conducted to investigate the association of N-terminal pro-B-type natriuretic peptide (NT-pro-BNP) levels with LV remodeling on magnetic resonance imaging and procollagen formation in 17 healthy controls and 24 patients with nonobstructive HC attributable to an identical Asp175Asn (aspartic acid to asparagine at codon 175) mutation in the alpha-tropomyosin gene. None of the patients had history of decompensated heart failure, and all patients had normal LV ejection fraction. Patients with HC had higher NT-pro-BNP levels compared with controls (median 60 pmol/L, range <40 to 359, vs <40 pmol/L; p <0.001), but 9 patients with HC had normal NT-pro-BNP levels (<40 pmol/L). In patients with HC, levels of NT-pro-BNP were correlated significantly with LV end-systolic volume index (r = 0.50, p <0.05), LV mass index (r = 0.47, p <0.05), proportion of hypokinetic segments (r = 0.50, p <0.05), and levels of serum aminoterminal propeptide of type III procollagen (r = 0.52, p <0.01). When patients with HC were divided into 3 groups on the basis of their NT-pro-BNP levels, there were statistically significant linear associations of LV end-systolic volume (test for linearity p = 0.034), LV mass index (p = 0.009), proportion of hypokinetic segments (p = 0.016), and levels of serum aminoterminal propeptide of type III procollagen (p = 0.020) with NT-pro-BNP levels over the 3 groups, suggesting a tight relation between LV remodeling and levels of NT-pro-BNP. In conclusion, in patients with nonobstructive HC attributable to an Asp175Asn mutation in the alpha-tropomyosin gene, elevated NT-pro-BNP levels are associated with incipient LV remodeling, suggesting that NT-pro-BNP could be used to diagnose insidious unfavorable LV remodeling in HC.

Natriuretic peptides in cardiovascular diseases

The natriuretic peptide family comprises atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), dendroaspis natriuretic peptide (DNP), and urodilatin. The activities of natriuretic peptides and endothelins are strictly associated with each other. ANP and BNP inhibit endothelin-1 (ET-1) production. ET-1 stimulates natriuretic peptide synthesis. All natriuretic peptides are synthesized from polypeptide precursors. Changes in natriuretic peptides and endothelin release were observed in many cardiovascular diseases: e.g. chronic heart failure, left ventricular dysfunction and coronary artery disease.

Relationship between natriuretic peptides and inflammation: proteomic evidence obtained during acute cellular cardiac allograft rejection in humans

BACKGROUND

Cardiac natriuretic peptides (NPs) atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) are polypeptide hormones secreted by the heart. Previously, we found that BNP, but not ANF, plasma levels may increase during an acute cellular cardiac allograft rejection episode. In vitro, the pro-inflammatory cytokines interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) produced a selective increase of BNP gene expression and secretion. Other pro-inflammatory cytokines had no such effects.

METHODS

We identified cytokines associated with the selective upregulation of BNP during cardiac allograft rejection using a proteomics approach to measure 120 cytokines and related substances in the plasma of 16 transplant patients before, during and after an acute rejection episode. The values obtained were correlated with BNP plasma levels. Cytokines identified as being significantly related to BNP plasma levels were tested in neonatal rat ventricular cardiocytes in culture for their ability to selectively promote BNP secretion. The signaling pathway related to this phenomenon was pharmacologically characterized.

RESULTS

Regulated-on-activation, normal T-expressed and secreted (RANTES), neutrophil-activating protein-2 (NAP-2) and insulin growth factor binding protein-1 (IGFBP-1) had significant correlations with BNP plasma levels during Grade 3A (Grade 2 revised [2R]) or above rejection as diagnosed by endomyocardial biopsy score according to the International Society for Heart and Lung Transplantation (ISHLT) grading system. In rat neonatal ventricular cardiocyte cultures, IGFBP-1 and RANTES were capable of promoting BNP, but not ANF secretion, as observed in rejecting patients. The BNP-promoting secretion activity of the identified cytokines was abolished by SB203580, a specific p38 MAP kinase inhibitor.

CONCLUSIONS

This work shows that cytokines other than pro-inflammatory cytokines correlate with BNP plasma levels observed during acute cardiac allograft rejection, and that the substances identified have in common p38 signaling. This finding provides a unifying mechanistic explanation regarding the relationship between inflammation and cardiac hormone production in acute cardiac allograft rejection.

Natriuretic peptide C receptor signalling in the heart and vasculature

Natriuretic peptides (NPs), including atrial, brain and C-type natriuretic peptides (ANP, BNP and CNP), bind two classes of cell surface receptors: the guanylyl cyclase-linked A and B receptors (NPR-A and NPR-B) and the C receptor (NPR-C). The biological effects of NPs have been mainly attributed to changes in intracellular cGMP following their binding to NPR-A and NPR-B. NPR-C does not include a guanylyl cyclase domain. It has been denoted as a clearance receptor and is thought to bind and internalize NPs for ultimate degradation. However, a substantial body of biochemical work has demonstrated the ability of NPR-C to couple to inhibitory G proteins (Gi) and cause inhibition of adenylyl cyclase and activation of phospholipase-C. Recently, novel physiological effects of NPs, mediated specifically by NPR-C, have been discovered in the heart and vasculature. We have described the ability of CNP, acting via NPR-C, to selectively inhibit L-type calcium currents in atrial and ventricular myocytes, as well as in pacemaker cells (sinoatrial node myocytes). In contrast, our studies of the electrophysiological effects of CNP on cardiac fibroblasts demonstrated an NPR-C-Gi-phospholipase-C-dependent activation of a non-selective cation current mediated by transient receptor potential (TRP) channels. It is also known that CNP and BNP have important anti-proliferative effects in cardiac fibroblasts that appear to involve NPR-C. In the mammalian resistance vessels, including mesenteric and coronary arteries, CNP has been found to function as an NPR-C-dependent endothelium-derived hyperpolarizing factor that regulates local blood flow and systemic blood pressure by hyperpolarizing smooth muscle cells. In this review we highlight the role of NPR-C in mediating these NP effects in myocytes and fibroblasts from the heart as well as in vascular smooth muscle cells.

Usefulness of BNP-administration in cardiac surgery: animal model

OBJECTIVE

The pharmacologic properties of Brain natriuretic peptide make it a favourable substance to use after cardiac operations. The goal of this study was to evaluate the effect of BNP following cardio-pulmonary bypass (CPB).

METHOD

Nineteen pigs were operated on using CPB. One group received BNP and the control group received placebo. A 30-minute ischemic episode was simulated. Following declamping, BNP was administered by an IV bolus, followed by an infusion for 60 minutes. Hemodynamic and clinical chemistry parameters were documented, as well as the amount of catecholamines.

RESULTS

The Cardiac output and Cardiac Index in the BNP group were significantly higher 60 minutes after ending CPB. Seven of ten animals in the control group needed catecholamines at the end of the experiment, whereas none of the animals in the BNP group did at this juncture. Creatine kinase and Lactate were significantly lower.

CONCLUSION

BNP is a well-tolerated agent that could present a new treatment option for heart failure following cardiac surgery. Hemodynamics are greatly improved with almost no need for pharmacological support.

Recombinant vascular endothelial growth factor 121 attenuates hypertension and improves kidney damage in a rat model of preeclampsia

Inhibitors of angiogenic factors are known to be upregulated, and their levels increase in the maternal circulation before the onset of preeclampsia. We reproduced a previously characterized model of preeclampsia by adenoviral overexpression of the soluble vascular endothelial growth factor (VEGF) receptor sFlt-1 (also referred to as sVEGFR-1) in pregnant and nonpregnant Sprague-Dawley rats. Animals were treated with VEGF121 at 0, 100, 200, or 400 microg/kg once or twice daily (n=8 per group; 64 total) and compared with normal control animals (n=4 per group) by examination of systolic blood pressure, urinary albumin and creatinine, renal histopathology, and glomerular gene expression profiling. sFlt-1 expression induced hypertension with proteinuria and glomerular endotheliosis and significant changes in gene expression. VEGF121 treatment alleviated these symptoms and reversed 125 of 268 sFlt-1-induced changes in gene expression. VEGF121 had beneficial effects in this rat model of preeclampsia without apparent harm to the fetus. Further study of VEGF121 as a potential therapeutic agent for preeclampsia is warranted.

Inhibition of Tgf beta signaling by endogenous retinoic acid is essential for primary lung bud induction

Disruption of retinoic acid (RA) signaling during early development results in severe respiratory tract abnormalities, including lung agenesis. Previous studies suggest that this might result from failure to selectively induce fibroblast growth factor 10 (Fgf10) in the prospective lung region of the foregut. Little is known about the RA-dependent pathways present in the foregut that may be crucial for lung formation. By performing global gene expression analysis of RA-deficient foreguts from a genetic [retinaldehyde dehydrogenase 2 (Raldh2)-null] and a pharmacological (BMS493-treated) mouse model, we found upregulation of a large number of Tgfbeta targets. Increased Smad2 phosphorylation further suggested that Tgfbeta signaling was hyperactive in these foreguts when lung agenesis was observed. RA rescue of the lung phenotype was associated with low levels of Smad2 phosphorylation and downregulation of Tgfbeta targets in Raldh2-null foreguts. Interestingly, the lung defect that resulted from RA-deficiency could be reproduced in RA-sufficient foreguts by hyperactivating Tgfbeta signaling with exogenous TGF beta 1. Preventing activation of endogenous Tgfbeta signaling with a pan-specific TGFbeta-blocking antibody allowed bud formation and gene expression in the lung field of both Raldh2-null and BMS493-treated foreguts. Our data support a novel mechanism of RA-Tgfbeta-Fgf10 interactions in the developing foregut, in which endogenous RA controls Tgfbeta activity in the prospective lung field to allow local expression of Fgf10 and induction of lung buds.

Inhibition of TGF-beta induced lung fibroblast to myofibroblast conversion by phosphodiesterase inhibiting drugs and activators of soluble guanylyl cyclase

Pulmonary fibroblast to myofibroblast conversion is a pathophysiological feature of idiopathic pulmonary fibrosis and COPD. This conversion is induced by transforming growth factor (TGF)-beta derived from epithelial cells as well as activated macrophages that have infiltrated the lung. Preventing this conversion might be a favourable therapeutic approach. Within this study we examined the activity of different members of the phosphodiesterase (PDE) family in primary human lung fibroblasts and various lung fibroblast cell lines both before and after TGF-beta induced differentiation to myofibroblasts as reflected by the expression of alpha-smooth muscle actin. We showed that the predominant PDE activities in lung fibroblasts are attributed to PDE5, PDE1 and to a smaller extent to PDE4. cyclic GMP (cGMP)-hydrolyzing activity declines by about half after differentiation to myofibroblasts in all pulmonary fibroblasts investigated, which is accompanied by a down-regulation of PDE5 protein. Lung fibroblast to myofibroblast differentiation is blocked by treatment with the PDE4 inhibitor piclamilast alone, depending on the TGF-beta concentration applied, and in combination with prostaglandin E(2) (PGE(2)) in a synergistic manner. Despite the high PDE5 activity the PDE5 inhibitor sildenafil by itself as well as in combination with brain natriuretic peptide or the nitric oxide-donor DETA-NONOate shows no inhibiting effects. However, combining sildenafil with the guanylyl cyclase (GC) activator BAY58-2667 and ODQ (which sensitizes GC for activation by BAY58-2667) suppressed TGF-beta induced differentiation. In summary, our data indicate that drugs interfering with the cyclic AMP (cAMP)-as well as with the NO-cGMP-pathway offer the therapeutic opportunity to prevent the differentiation of pulmonary fibroblasts to myofibroblasts in lung fibrosis.

The presence of B-type natriuretic peptide in burns and the responsiveness of fibroblasts to BNP: proof of principle

BACKGROUND

B-type natriuretic peptide (BNP) released from cardiac myocytes plays an important role in cardiac homeostasis through cyclic guanosine monophosphate (cGMP) activation. BNP also reduces cardiac remodeling and fibrosis. The antifibrotic effects of BNP are mediated in part by blocking the effects of transforming growth factor beta, a profibrotic cytokine that plays a significant role in cutaneous wound healing. It is unclear if BNP plays any role in cutaneous wound healing.

OBJECTIVES

To investigate if BNP levels would be elevated in thermally injured human skin and if human-derived fibroblasts would respond to BNP exposure by increasing levels of cGMP.

METHODS

This was an in vitro analysis of human skin. Skin samples and cells were collected from patients with and without thermal injury. The authors stained three skin samples from normal skin (taken at the time of elective cosmetic surgery) with antibodies to BNP and compared these with three tissue samples obtained from burned human skin taken during tangential excision of deep burns. Normal human-derived fibroblasts and keratinocytes were exposed in triplicate to BNP in vitro, and cGMP accumulation was evaluated. Levels of cGMP were quantified and compared with analysis of variance.

RESULTS

BNP was present in all specimens of thermally injured skin (especially around collagen, epithelial cells, and endothelial cells) but not in any uninjured skin samples (p = 0.05, single-tailed Fisher's exact test). In vitro grown fibroblasts showed significant increases of cGMP levels with increasing levels of BNP exposure (mean [+/-SD]: 0.6 [+/-0.3], 1.2 [+/-0.2], 4.6 [+/-0.1], and 5.0 [+/-0.9] pmol/mL with BNP concentrations of 0, 10, 500, and 1,000 nmol/L, respectively; p < 0.001). The effect of BNP on keratinocytes was minimal and below the level of quantification.

CONCLUSIONS

These findings demonstrate proof of principle that human fibroblasts are responsive to the effects of BNP in vitro and that BNP is present in injured skin, suggesting that BNP may play a role in cutaneous wound healing.

Increased Brain Natriuretic Peptide Secretion is a Marker of Disease Progression in Nonobstructive Hypertrophic Cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is associated with increased plasma brain natriuretic peptide (BNP), but sequential plasma and myocardial BNP assessment in stable and dilated HCM has never been performed.

METHODS AND RESULTS

Forty consecutive HCM patients (42 +/- 8 years, 25 males) underwent cardiac catheterization, angiography, and left ventricular (LV) endomyocardial biopsy. During follow-up (70.5 +/- 6.7 months), 30 patients (Group 1) remained stable whereas 10 patients (Group 2) progressed to dilated phase. Group 2 patients underwent a second invasive study with LV biopsy. BNP plasma levels were measured at baseline and at follow-up in all patients. All biopsies were processed for histology and immunohistochemistry with anti-BNP antibodies. BNP plasma levels remained unchanged in Group 1, whereas it significantly increased in all Group 2 patients who exhibited an elevation of LV and right ventricular end-diastolic pressure. Immunohistochemistry showed an increase of BNP-positive myocytes in follow-up biopsies when compared with baseline (75.0 +/- 15.0 % versus 29.8 +/- 10.0 %; P = .005) with a significant correlation with LV end-diastolic pressure (r = 0.78, P < .001) and plasma BNP (r = 0.83, P < .001).

CONCLUSIONS

Progression to end-stage of HCM is characterized by further increase of myocardial and plasma BNP. Serial assessment of plasma BNP may provide noninvasive recognition of hemodynamic deterioration, allowing prompt institution of heart failure therapy.

Increased connective tissue growth factor relative to brain natriuretic peptide as a determinant of myocardial fibrosis

Excessive fibrosis contributes to an increase in left ventricular stiffness. The goal of the present study was to investigate the role of connective tissue growth factor (CCN2/CTGF), a profibrotic cytokine of the CCN (Cyr61, CTGF, and Nov) family, and its functional interactions with brain natriuretic peptide (BNP), an antifibrotic peptide, in the development of myocardial fibrosis and diastolic heart failure. Histological examination on endomyocardial biopsy samples from patients without systolic dysfunction revealed that the abundance of CTGF-immunopositive cardiac myocytes was correlated with the excessive interstitial fibrosis and a clinical history of acute pulmonary congestion. In a rat pressure overload cardiac hypertrophy model, CTGF mRNA levels and BNP mRNA were increased in proportion to one another in the myocardium. Interestingly, relative abundance of mRNA for CTGF compared with BNP was positively correlated with diastolic dysfunction, myocardial fibrosis area, and procollagen type 1 mRNA expression. Investigation with conditioned medium and subsequent neutralization experiments using primary cultured cells demonstrated that CTGF secreted by cardiac myocytes induced collagen production in cardiac fibroblasts. Further, G protein-coupled receptor ligands induced expression of the CTGF and BNP genes in cardiac myocytes, whereas aldosterone and transforming growth factor-beta preferentially induced expression of the CTGF gene. Finally, exogenous BNP prevented the production of CTGF in cardiac myocytes. These data suggest that a disproportionate increase in CTGF relative to BNP in cardiac myocytes plays a central role in the induction of excessive myocardial fibrosis and diastolic heart failure.

Examining potential therapies targeting myocardial fibrosis through the inhibition of transforming growth factor-beta 1

After injury, the heart undergoes a remodeling process consisting primarily of myocyte hypertrophy, apoptosis and interstitial fibrosis. Although initially beneficial, excess fibrosis gradually results in alteration of left ventricular properties and cardiac dysfunction. Transforming growth factor-beta 1 (TGF-beta(1)) is thought to be a primary mediator of fibrosis within the heart after injury. Currently, angiotensin II blockade is used to inhibit the actions of TGF-beta(1). However, recent studies indicate that angiotensin II blockade alone may not be sufficient to prevent TGF-beta(1)-induced fibrosis. Thus far, both in vivo and in vitro models have shown that direct TGF-beta(1) inhibition, NAPDH oxidase inhibitors, growth factors and hormonal treatment regimens targeting TGF-beta(1) may significantly reduce cardiac fibrosis after injury. This study attempts to underline these alternatives to angiotensin II blockade in combating TGF-beta(1)-induced cardiac dysfunction.

BNP-induced activation of cGMP in human cardiac fibroblasts: interactions with fibronectin and natriuretic peptide receptors

Cardiac remodeling involves the accumulation of extracellular matrix (ECM) proteins including fibronectin (FN). FN contains RGD motifs that bind integrins at DDX sequences allowing signaling from the ECM to the nucleus. We noted that the natriuretic peptide receptor A (NPR-A) sequence contains both RGD and DDX sequences. The goal of the current investigation was to determine potential interactions between FN and NPR-A on BNP induction of cGMP in cultured human cardiac fibroblasts (CFs). Further, we sought to determine whether a Mayo designed NPR-A specific RGD peptide could modify this interaction. Here we reconfirm the presence of all three natriuretic peptide receptors (NPR) in CFs. CFs plated on FN demonstrated a pronounced increase in cGMP production to BNP compared to non-coated plates. This production was also enhanced by the NPR-A specific RGD peptide, which further augmented FN associated cGMP production. Addition of HS-142-1, a NPR-A/B antagonist, abrogated the responses of BNP to both FN and the NPR-A specific RGD peptide. Finally, we defined a possible role for the NPR-C through non-cGMP mechanisms in mediating the anti-proliferative actions of BNP in CFs where the NPR-C antagonist cANF 4-28 but not HS-142-1 blocked BNP-mediated inhibition of proliferation of CFs. We conclude that NPR-A interacts with components of the ECM such as FN to enhance BNP activation of cGMP and that a small NPR-A specific RGD peptide augments this action of BNP with possible therapeutic implications. Lastly, the NPR-C may also have a role in mediating anti-proliferative actions of BNP in CFs.

Brain Natriuretic Peptide Levels and Left Ventricular Functional Recovery in a Chronic Heart Failure Population

Due to the poor correlation between symptoms and left ventricular (LV) ejection fraction in a chronic heart failure (HF) population, the ability to identify patients who demonstrate LV functional recovery poses a dilemma for the clinician. Serial echocardiograms are not practical in a large outpatient HF population. Plasma brain natriuretic peptide (BNP) levels have a high predictive value for excluding patients with ventricular dysfunction and therefore could serve as a marker for identifying patients who demonstrate improved LV function. To evaluate this point, the researchers obtained baseline BNP levels in 380 chronic systolic HF patients seen in an outpatient HF clinic. Each patient already had a baseline echocardiogram performed before or on entry into the clinic. Fifty patients were identified in this group as having normal BNP levels (< or = 100 pg/mL). Echocardiograms were then repeated in this group and compared with initial echocardiographic data obtained from a retrospective chart review. The results showed that the mean LV ejection fraction for the group was increased (p < 0.001), mean LV internal dimension was decreased (p < 0.001), and the number of patients with an ejection fraction > 50% increased from zero to 20 (p < 0.001). Thus, normal BNP levels can correlate with LV recovery and could potentially offer a cost-effective method of assessing changes in LV function in patients with chronic HF.

C-type natriuretic peptide activates a non-selective cation current in acutely isolated rat cardiac fibroblasts via natriuretic peptide C receptor-mediated signalling

In the heart, fibroblasts play an essential role in the deposition of the extracellular matrix and they also secrete a number of hormonal factors. Although natriuretic peptides, including C-type natriuretic peptide (CNP) and brain natriuretic peptide, have antifibrotic effects on cardiac fibroblasts, the effects of CNP on fibroblast electrophysiology have not been examined. In this study, acutely isolated ventricular fibroblasts from the adult rat were used to measure the effects of CNP (2 x 10(-8) M) under whole-cell voltage-clamp conditions. CNP, as well as the natriuretic peptide C receptor (NPR-C) agonist cANF (2 x 10(-8) M), significantly increased an outwardly rectifying non-selective cation current (NSCC). This current has a reversal potential near 0 mV. Activation of this NSCC by cANF was abolished by pre-treating fibroblasts with pertussis toxin, indicating the involvement of G(i) proteins. The cANF-activated NSCC was inhibited by the compounds Gd(3+), SKF 96365 and 2-aminoethoxydiphenyl borate. Quantitative RT-PCR analysis of mRNA from rat ventricular fibroblasts revealed the expression of several transient receptor potential (TRP) channel transcripts. Additional electrophysiological analysis showed that U73122, a phospholipase C antagonist, inhibited the cANF-activated NSCC. Furthermore, the effects of CNP and cANF were mimicked by the diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG), independently of protein kinase C activity. These are defining characteristics of specific TRPC channels. More detailed molecular analysis confirmed the expression of full-length TRPC2, TRPC3 and TRPC5 transcripts. These data indicate that CNP, acting via the NPR-C receptor, activates a NSCC that is at least partially carried by TRPC channels in cardiac fibroblasts.

Oral Brain Natriuretic Peptide: A Novel Strategy for Chronic Protein Therapy for Cardiovascular Disease

In 1956, secretory granules were detected via electron microscopy in the mammalian atria by Kisch. This remarkable discovery signaled the beginning of a new field of research that decades later has lead to the concept of the heart as an endocrine organ and the establishment of the natriuretic peptide (NP) system. In 1981, deBold and colleagues identified from the atrial myocardium the first member of the NP family, atrial NP. Thereafter, new members of this growing family of cardiac hormones were identified and investigated. The successful story of B-type or brain NP (BNP), from its discovery to its use in the diagnosis and prognosis of cardiovascular diseases and later as a tool in the treatment of acute congestive heart failure, have since taken place. However, the use of peptides as chronic therapies has been limited by enzymatic degradation. Chronic administration of BNP, particularly in disease states like hypertension and early heart failure, could be effective as an antihypertensive therapy and in delaying progression of cardiac disease. To date, the use of BNP is limited to patients with acute decompensated heart failure, but new strategies are under investigation to extend the use of chronic BNP in less severe stages of cardiovascular diseases. Innovative technologies have been recently developed that allow protection of proteins from enzymatic degradation, making feasible oral administration of small proteins such as BNP. This review will focus on the potential role of BNP as a new chronic therapeutic strategy in the treatment of cardiovascular diseases and will summarize our recent report of the development and in vivo evaluation of orally active human BNP.

Plasma B vitamins and their relation to the severity of chronic heart failure

BACKGROUND

Total homocysteine (tHcy) has been linked to the severity of chronic heart failure (CHF). Elevated tHcy concentrations are mainly caused by folate and vitamin B-12 deficiencies.

OBJECTIVE

We hypothesized that folate and vitamin B-12 deficiencies can explain the relation between tHcy and the severity of CHF.

DESIGN

We investigated 987 CHF patients. All subjects underwent a physical examination and blood sampling. Cardiac catheterization was performed in 929 patients and echocardiography in 460 patients. Serum tHcy, folate, vitamin B-12, and N-terminal pro-B-type natriuretic-peptide (NT-proBNP) were measured and renal and hepatic function were studied.

RESULTS

tHcy increased with increasing New York Heart Association (NYHA) classes of heart failure (P < 0.001) and correlated with the left ventricular ejection fraction (EF; r = -0.150, P < 0.001). Contrary to the hypothesis, vitamin B-12 (P < 0.001) increased with NYHA class (P < 0.001) and was negatively correlated with EF (r = -0.080, P = 0.015). Folate showed no relation with NYHA class or EF. Comparable results were obtained for NT-proBNP (tHcy: r = 0.27, P < 0.001; vitamin B-12: r = 0.091, P = 0.004; folate: r = -0.045, P = 0.169). The correlations between tHcy, EF, and NT-proBNP were significantly stronger in patients without coronary artery disease (CAD) than in those with CAD. Regression analysis showed that tHcy, but not B vitamins, is a strong predictor of EF and NT-proBNP.

CONCLUSIONS

This study showed that tHcy, but not folate and vitamin B-12, is related to clinical, echocardiographic, and laboratory variables of CHF, which indicates a relation between tHcy and the severity of CHF. This relation is stronger in patients without CAD. The lack of association of folate and the paradoxical relation of vitamin B-12 with CHF can possibly be explained by a disturbance in hepatic homeostasis.

Effect of AT2 blockade on cardiac hypertrophy as induced by high dietary salt in the proatrial natriuretic peptide (ANP) gene-disrupted mouse

The role of the angiotensin II type 2 receptor (AT2) during alterations in cardiac size remains largely unclear. Through employment of an AT2 antagonist, the present study explored a possible involvement of the AT2 receptor during salt-induced cardiac hypertrophy in the proatrial natriuretic peptide gene-disrupted mouse (ANP-/-). ANP-/- mice received either saline solution or the AT2 antagonist, PD123319, and were then placed on a high salt diet (8.0% NaCl) for 3 weeks. Cardiac and pulmonary size, expression of the renin-angiotensin system (RAS), and the behaviour of various hypertrophy marker genes were assessed. PD123319 caused enhanced expression of the systemic RAS, yet the cardiac RAS was largely unaffected. Although AT2 blockade did not alter whole cardiac mass, right ventricle mass, as well as pulmonary mass-to-body mass ratios were significantly decreased. Collagen type I was decreased in the latter tissues, likely contributing to the regression in mass. Several players essential in the maintenance of myocardial extracellular matrix homeostasis including B-type natriuretic peptide, matrix metalloproteinase-2, tumour necrosis factor, and transforming growth factor were also significantly altered by PD123319. These data suggest that AT2 blockade is involved in significant changes in myocardial extracellular matrix components translating into decreases in tissue mass in the salt-sensitive ANP-/- animal.

EPLERENONE PREVENTS ADVERSE CARDIAC REMODELLING INDUCED BY PRESSURE OVERLOAD IN ATRIAL NATRIURETIC PEPTIDE-NULL MICE

1. Atrial natriuretic peptide (ANP)-null mice (Nppa(-/-)) exhibit cardiac hypertrophy at baseline and adverse cardiac remodelling in response to transverse aortic constriction (TAC)-induced pressure overload stress. Previous studies have suggested that natriuretic peptides could potentially oppose mineralocorticoid signalling at several levels, including suppression of adrenal aldosterone production, inhibition of mineralocorticoid receptor (MR) activation or suppression of MR-mediated production of pro-inflammatory factors. Thus, we hypothesized that the MR blocker eplerenone would prevent the exaggerated left ventricular (LV) remodelling/fibrosis and dysfunction after TAC in Nppa(-/-). 2. In the present study, Nppa(-/-) and wild-type Nppa(+/+) mice fed eplerenone- or vehicle (oatmeal)-supplemented chow since weaning were subjected to TAC or sham operation. The daily dose of eplerenone administered was approximately 200 mg/kg. At 1 week after TAC, LV size and function were evaluated by echocardiogram and LV cross-sections were stained with picrosirius red for collagen volume measurement. Total RNA was extracted from the LV for real-time polymerase chain reaction analysis of osteopontin. 3. Eplerenone had no effect on baseline hypertrophy observed in sham-operated Nppa(-/-) compared with Nppa(+/+) mice. Eplerenone attenuated the TAC-induced increase in LV weight in both genotypes and completely prevented LV dilation, systolic dysfunction and interstitial collagen deposition seen in Nppa(-/-) mice after TAC. However, serum aldosterone levels were lower in Nppa(-/-) compared with Nppa(+/+) wild types. No interaction between eplerenone and genotype in osteopontin mRNA levels was observed. 4. Eplerenone prevents adverse cardiac remodelling related to pressure overload in ANP-deficient mice, mainly due to an antifibrotic effect. The mechanism whereby ANP deficiency leads to excess hypertrophy, fibrosis and early failure following TAC is increased profibrotic signals resulting from excess or unopposed MR activation, rather than increased levels of aldosterone.

Membrane guanylyl cyclase receptors: an update

Recent studies have demonstrated key roles for several membrane guanylyl cyclase receptors in the regulation of cell hyperplasia, hypertrophy, migration and extracellular matrix production, all of which having an impact on clinically relevant diseases, including tissue remodeling after injury. Additionally, cell differentiation, and even tumor progression, can be profoundly influenced by one or more of these receptors. Some of these receptors also mediate important communication between the heart and intestine, and the kidney to regulate blood volume and Na+ balance.

Earliest changes in the left ventricular transcriptome postmyocardial infarction

We report a genome-wide survey of early responses of the mouse heart transcriptome to acute myocardial infarction (AMI). For three regions of the left ventricle (LV), namely, ischemic/infarcted tissue (IF), the surviving LV free wall (FW), and the interventricular septum (IVS), 36,899 transcripts were assayed at six time points from 15 min to 48 h post-AMI in both AMI and sham surgery mice. For each transcript, temporal expression patterns were systematically compared between AMI and sham groups, which identified 515 AMI-responsive genes in IF tissue, 35 in the FW, 7 in the IVS, with three genes induced in all three regions. Using the literature, we assigned functional annotations to all 519 nonredundant AMI-induced genes and present two testable models for central signaling pathways induced early post-AMI. First, the early induction of 15 genes involved in assembly and activation of the activator protein-1 (AP-1) family of transcription factors implicates AP-1 as a dominant regulator of earliest post-ischemic molecular events. Second, dramatic increases in transcripts for arginase 1 (ARG1), the enzymes of polyamine biosynthesis, and protein inhibitor of nitric oxide synthase (NOS) activity indicate that NO production may be regulated, in part, by inhibition of NOS and coordinate depletion of the NOS substrate, L: -arginine. ARG1: was the single-most highly induced transcript in the database (121-fold in IF region) and its induction in heart has not been previously reported.

Genetic bases of arrhythmogenic right ventricular Cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a heart muscle disease in which the pathological substrate is a fibro-fatty replacement of the right ventricular myocardium. The major clinical features are different types of arrhythmias with a left branch block pattern. ARVC shows autosomal dominant inheritance with incomplete penetrance. Recessive forms were also described, although in association with skin disorders.

Ten genetic loci have been discovered so far and mutations were reported in five different genes. ARVD1 was associated with regulatory mutations of transforming growth factor beta-3 (TGFβ3), whereas ARVD2, characterized by effort-induced polymorphic arrhythmias, was associated with mutations in cardiac ryanodine receptor-2 (RYR2). All other mutations identified to date have been detected in genes encoding desmosomal proteins: plakoglobin (JUP) which causes Naxos disease (a recessive form of ARVC associated with palmoplantar keratosis and woolly hair); desmoplakin (DSP) which causes the autosomal dominant ARVD8 and plakophilin-2 (PKP2) involved in ARVD9. Desmosomes are important cell-to-cell adhesion junctions predominantly found in epidermis and heart; they are believed to couple cytoskeletal elements to plasma membrane in cell-to-cell or cell-to-substrate adhesions.

The broad homeostatic role of natriuretic peptides

A brief non-inclusive review on natriuretic peptides (NP), their receptors, and their main functional properties is presented. The three main NP, atrial (ANP), brain (BNP) and C-type (CNP) are considered. Guanylyl cyclase receptors modulate all the known systemic effects of NP. Clearance receptors determine the metabolic disposal of NP and in this manner regulate their plasma levels and/or local tissue concentrations. Structure-function properties, and homeostatic properties of NP receptors are presented. ANP, which plays a major role in pressure-volume homeostasis, is discussed in relationship to its effects on renal hemodynamic and excretory functions, inhibition of the renin-angiotensin-aldosterone system, vasorelaxant, and third-spacing action. For BNP special attention is directed to its role as a negative modulator of ventricular remodeling, in view of its anti-hypertrophic, anti-fibrotic and anti-inflammatory effects in the heart. The major effect of CNP in promoting vertebral and longitudinal bone growth is briefly addressed. Finally, emphasis is placed on the recent discovery that ANP affects fat metabolism in humans due to its powerful lipolytic action.

Role of aldosterone blockade for treatment of heart failure and post-acute myocardial infarction

Heart failure continues to significantly impact morbidity and mortality after acute myocardial infarction (AMI), especially when associated with left ventricular systolic dysfunction (LVSD). Therefore, routine use of optimal therapy for patients with heart failure after AMI is needed in the future. Data from the Eplerenone Post-Acute Myocardial Infarction Heart Failure Efficacy and Survival Study (EPHESUS) has demonstrated that addition of eplerenone to standard therapy in patients with LVSD and clinical heart failure post-AMI significantly improves outcomes in these patients, providing the basis for acceptance of aldosterone blockade as an integral component of therapy. However, further studies are needed to more broadly explore the usefulness of aldosterone blockade in heart failure therapy. As research clarifies the many complex pathophysiologic processes involved in post-AMI remodeling, treatment should continue to move beyond symptom-targeted therapies to disease- and mechanism-targeted therapies that will further improve outcomes in the setting of heart failure post-AMI and beyond.

Transforming Growth Factor-β Receptor Type 1 (TGFβRI) Kinase Activity but Not p38 Activation Is Required for TGFβRI-Induced Myofibroblast Differentiation and Profibrotic Gene Expression

Transforming growth factor-beta (TGFbeta) is a major mediator of normal wound healing and of pathological conditions involving fibrosis, such as idiopathic pulmonary fibrosis. TGFbeta also stimulates the differentiation of myofibroblasts, a hallmark of fibrotic diseases. In this study, we examined the underlying processes of TGFbetaRI kinase activity in myofibroblast conversion of human lung fibroblasts using specific inhibitors of TGFbetaRI (SD-208) and p38 mitogen-activated kinase (SD-282). We demonstrated that SD-208, but not SD-282, inhibited TGFbeta-induced SMAD signaling, myofibroblast transformation, and collagen gel contraction. Furthermore, we extended our findings to a rat bleomycin-induced lung fibrosis model, demonstrating a significant decrease in the number of myofibroblasts at fibroblastic foci in animals treated with SD-208 but not those treated with SD-282. SD-208 also reduced collagen deposition in this in vivo model. Microarray analysis of human lung fibroblasts identified molecular fingerprints of these processes and showed that SD-208 had global effects on reversing TGFbeta-induced genes involved in fibrosis, inflammation, cell proliferation, cytoskeletal organization, and apoptosis. These studies also revealed that although the p38 pathway may not be needed for appearance or disappearance of the myofibroblast, it can mediate a subset of inflammatory and fibrogenic events of the myofibroblast during the process of tissue repair and fibrosis. Our findings suggest that inhibitors such as SD-208 may be therapeutically useful in human interstitial lung diseases and pulmonary fibrosis.

The natriuretic peptide system: kidney and cardiovascular effects

PURPOSE OF REVIEW

The natriuretic peptide (NP) system is primarily an endocrine system that maintains fluid and pressure homeostasis by modulating cardiac and renal function. The physiologic functions of the NP system in healthy humans and in patients with cardiovascular disease are not fully understood. NP levels are elevated in patients with heart failure (HF) and other cardiac diseases; measurement of NPs may be used in the clinical setting to aid diagnosis and prognosis. In addition, synthetic NPs such as nesiritide are available for use in management of patients with acutely decompensated congestive HF.

RECENT FINDINGS

Not only do NPs modulate volume and pressure homeostasis, but they also exert important anti-proliferative, anti-fibrotic effects in the heart. Thus, NPs may prove useful for prevention of remodeling after myocardial infarction and in advanced HF. BNP is emerging as an important biomarker in patients with HF and other cardiovascular diseases, such as pulmonary hypertension and atherosclerotic vascular disease. Elevated NP levels may serve as an early warning system to help to identify patients at high risk for cardiac events. Recombinant human ANP (carperitide) and BNP (nesiritide) are useful for management of acutely decompensated HF; these drugs are also being investigated for myocardial and renal protection in the setting of cardiac surgery and for prevention of cardiac remodeling.

SUMMARY

The clinical application of NPs is expanding rapidly. Recent basic science and clinical research findings continue to improve our understanding of the NP system and guide use of ANP and BNP as biomarkers and as therapeutic agents.

Normalizing the bone marrow microenvironment with p38 inhibitor reduces multiple myeloma cell proliferation and adhesion and suppresses osteoclast formation

The multiple myeloma (MM) bone marrow (BM) microenvironment plays a critical role in supporting tumor growth and survival as well as in promoting formation of osteolytic lesions. Recent results suggest that the p38 mitogen-activated protein kinase (MAPK) is an important factor in maintaining this activated environment. In this report, we demonstrate that the p38alpha MAPK inhibitor, SCIO-469, suppresses secretion of the tumor-supportive factors IL-6 and VEGF from BM stromal cells (BMSCs) as well as cocultures of BMSCs with MM cells, resulting in reduction in MM cell proliferation. Additionally, we show that SCIO-469 prevents TNFalpha-induced adhesion of MM cells to BMSCs through an ICAM-1- and VCAM-1-independent mechanism. Microarray analysis revealed a novel set of TNFalpha-induced chemokines in BMSCs that is strongly inhibited by SCIO-469. Furthermore, reintroduction of chemokines CXCL10 and CCL8 to BMSCs overcomes the inhibitory effect of SCIO-469 on TNFalpha-induced MM adhesion. Lastly, we show that SCIO-469 inhibits secretion and expression of the osteoclast-activating factors IL-11, RANKL, and MIP-1alpha as well as prevents human osteoclast formation in vitro. Collectively, these results suggest that SCIO-469 treatment can suppress factors in the bone marrow microenvironment to inhibit MM cell proliferation and adhesion and also to alleviate osteolytic activation in MM.

A Constitutively Active Hypoxia-Inducible Factor-1α/VP16 Hybrid Factor Activates Expression of the Human B-Type Natriuretic Peptide Gene

Hypoxia-inducible factor-1 (HIF-1) is a primary regulator of the physiological response to hypoxia. A recombinant adenovirus expressing a constitutively active hybrid form of the HIF-1alpha subunit (Ad2/HIF-1alpha/VP16) is being evaluated as a gene therapy for the treatment of peripheral vascular disease. Ad2/HIF-1alpha/VP16 up-regulates known HIF-1-responsive genes, including those involved in angiogenesis. Expression profile analysis revealed that the brain natriuretic peptide (BNP) gene was significantly up-regulated in response to HIF-1alpha/VP16 in human fetal cardiac cells. Real-time reverse transcription-polymerase chain reaction analyses confirmed transcriptional activation of the BNP gene by HIF-1alpha/VP16 in human but not rat cardiac cells. Because hypoxia itself did not increase human BNP gene expression in these analyses, the mechanism of the HIF-1alpha/VP16 effect was determined. Analyses of promoter deletion mutants suggested that the cis-acting sequence in the human BNP promoter mediating activation by HIF-1alpha/VP16 was a putative HIF-1 responsive element (HRE) located at -466. An SV40 basal promoter-luciferase plasmid containing a minimal BNP HRE was up-regulated by HIF-1alpha/VP16, whereas a similar construct carrying a mutation within the HIF-1 binding site was not. Mutation of an E-box motif within the BNP HRE reduced HIF-1alpha/VP16-mediated transcriptional activation by 50%. Gel-shift analyses showed that both the native HIF-1alpha and HIF-1alpha/VP16 are able to bind to a probe containing the HIF-1 binding site. These experiments demonstrate the existence of a functional HRE in the BNP promoter and further define the scope and mechanism of action of Ad2/HIF-1alpha/VP16.

Pulmonary Hemodynamic Responses to Brain Natriuretic Peptide and Sildenafil in Patients With Pulmonary Arterial Hypertension

STUDY OBJECTIVES

Brain natriuretic peptide (BNP) blunts hypoxic pulmonary hypertension in animal models, but its acute hemodynamic effects in patients with pulmonary arterial hypertension (PAH) are not known. The aim of this study was to determine if human B-type natriuretic peptide is a safe and efficacious pulmonary vasodilator in patients with PAH and if the pulmonary hemodynamic effects are potentiated by phosphodiesterase inhibition.

DESIGN

Open-label study.

SETTING

Medical ICUs of three tertiary care hospitals in New England.

PATIENTS

Thirteen consecutive adult patients undergoing right-heart catheterization and a pulmonary vasodilator trial for the initial evaluation of PAH.

INTERVENTIONS

Patients were administered inhaled nitric oxide (iNO), i.v. epoprostenol, and a 3-h infusion of BNP alone and 1 h after an oral dose of the phosphodiesterase-5 inhibitor sildenafil.

RESULTS

iNO and sildenafil alone decreased mean pulmonary artery pressure (mPAP) without a significant fall in pulmonary vascular resistance (PVR). Epoprostenol decreased both mPAP and PVR. BNP alone had no significant effect on pulmonary hemodynamics, but the combination of sildenafil plus BNP decreased mPAP and PVR for up to 6 h after stopping BNP. The decrease in mPAP with sildenafil plus BNP (+/- SE) was greater than after 1 h of sildenafil alone (44.6 +/- 3.8 to 40.6 +/- 3.9 mm Hg, p = 0.027). An acute vasodilator response, defined as a decrease in mPAP > 10 mm Hg and end mPAP < 40 mm Hg, was seen in 0 of 8 patients with iNO, 1 of 13 patients with epoprostenol, 0 of 13 patients with BNP, and 4 of 12 patients with sildenafil plus BNP. BNP decreased mean systemic arterial pressure (5.6 +/- 2.8 mm Hg) but had no effect on cardiac output or systemic vascular resistance.

CONCLUSIONS

A 3-h BNP infusion does not significantly improve pulmonary hemodynamics in most patients with PAH but is well tolerated and augments the acute pulmonary vasodilator effect of sildenafil.

Natriuretic peptides, their receptors, and cyclic guanosine monophosphate-dependent signaling functions

Natriuretic peptides are a family of structurally related but genetically distinct hormones/paracrine factors that regulate blood volume, blood pressure, ventricular hypertrophy, pulmonary hypertension, fat metabolism, and long bone growth. The mammalian members are atrial natriuretic peptide, B-type natriuretic peptide, C-type natriuretic peptide, and possibly osteocrin/musclin. Three single membrane-spanning natriuretic peptide receptors (NPRs) have been identified. Two, NPR-A/GC-A/NPR1 and NPR-B/GC-B/NPR2, are transmembrane guanylyl cyclases, enzymes that catalyze the synthesis of cGMP. One, NPR-C/NPR3, lacks intrinsic enzymatic activity and controls the local concentrations of natriuretic peptides through constitutive receptor-mediated internalization and degradation. Single allele-inactivating mutations in the promoter of human NPR-A are associated with hypertension and heart failure, whereas homozygous inactivating mutations in human NPR-B cause a form of short-limbed dwarfism known as acromesomelic dysplasia type Maroteaux. The physiological effects of natriuretic peptides are elicited through three classes of cGMP binding proteins: cGMP-dependent protein kinases, cGMP-regulated phosphodiesterases, and cyclic nucleotide-gated ion channels. In this comprehensive review, the structure, function, regulation, and biological consequences of natriuretic peptides and their associated signaling proteins are described.

Natriuretic peptides: novel therapeutic targets in heart failure

Since the discovery of the cardiac hormone atrial natriuretic peptide by de Bold and colleagues in 1981, the field of natriuretic peptides has significantly advanced with translation of new knowledge to the clinical practice of heart failure. This new knowledge builds on the importance of cardiorenal mechanisms that contribute to optimal cardiovascular regulation. Recent investigations by our group and others have also established the direct myocardial actions of the natriuretic peptides, broadening their therapeutic potential beyond renal mechanisms. Indeed, a potential therapeutic target is cardiac remodeling and fibrosis based on the unique cardiorenal and humoral protective properties that natriuretic peptides possess. We review new insights into the natriuretic peptide system and specifically focus on the possible role of natriuretic peptides as a new therapeutic strategy to limit cardiac remodeling and fibrosis to delay worsening of cardiac function and the progression of heart failure.

Cardiac endocrine function is an essential component of the homeostatic regulation network: physiological and clinical implications

The discovery of cardiac natriuretic hormones required a profound revision of the concept of heart function. The heart should no longer be considered only as a pump but rather as a multifunctional and interactive organ that is part of a complex network and active component of the integrated systems of the body. In this review, we first consider the cross-talk between endocrine and contractile function of the heart. Then, based on the existing literature, we propose the hypothesis that cardiac endocrine function is an essential component of the integrated systems of the body and thus plays a pivotal role in fluid, electrolyte, and hemodynamic homeostasis. We highlight those studies indicating how alterations in cardiac endocrine function can better explain the pathophysiology of cardiovascular diseases and, in particular of heart failure, in which several target organs develop a resistance to the biological action of cardiac natriuretic peptides. Finally, we emphasize the concept that a complete knowledge of the cardiac endocrine function and of its relation with other neurohormonal regulatory systems of the body is crucial to correctly interpret changes in circulating natriuretic hormones, especially the brain natriuretic peptide.

PGE2 stimulates human brain natriuretic peptide expression via EP4 and p42/44 MAPK

Brain natriuretic peptide (BNP) produced by cardiac myocytes has antifibrotic and antigrowth properties and is a marker of cardiac hypertrophy. We previously showed that prostaglandin E2 (PGE2) is the main prostaglandin produced in myocytes treated with proinflammatory stimuli and stimulates protein synthesis by binding to its EP4 receptor. We hypothesized that PGE2, acting through EP4, also regulates BNP gene expression. We transfected neonatal ventricular myocytes with a plasmid encoding the human BNP (hBNP) promoter driving expression of a luciferase reporter gene. PGE2 increased hBNP promoter activity 3.5-fold. An EP4 antagonist reduced the stimulatory effect of PGE2 but not an EP1 antagonist. Because EP4 signaling can involve adenylate cyclase, cAMP, and protein kinase A (PKA), we tested the effect of H-89, a PKA inhibitor, on PGE2 stimulation of the hBNP promoter. H-89 at 5 muM decreased PGE2 stimulation of BNP promoter activity by 100%. Because p42/44 MAPK mediates the effect of PGE2 on protein synthesis, we also examined the role of MAPKs in the regulation of BNP promoter activity. PGE2 stimulation of the hBNP promoter was inhibited by a MEK1/2 inhibitor and a dominant-negative mutant of Raf, indicating that p42/44 MAPK was involved. In contrast, neither a p38 MAPK inhibitor nor a JNK inhibitor reduced the stimulatory effect of PGE2. Involvement of small GTPases was also studied. Dominant-negative Rap inhibited PGE2 stimulation of the hBNP promoter, but dominant-negative Ras did not. We concluded that PGE2 stimulates the BNP promoter mainly via EP4, PKA, Rap, and p42/44 MAPK.