Expression and control of C-type natriuretic peptide in rat vascular smooth muscle cells

Role of PDE10A in vascular smooth muscle cell hyperplasia and pathological vascular remodelling

AIMS

Intimal hyperplasia is a common feature of vascular remodelling disorders. Accumulation of synthetic smooth muscle cell (SMC)-like cells is the main underlying cause. Current therapeutic approaches including drug-eluting stents are not perfect due to the toxicity on endothelial cells and novel therapeutic strategies are needed. Our preliminary screening for dysregulated cyclic nucleotide phosphodiesterases (PDEs) in growing SMCs revealed the alteration of PDE10A expression. Herein, we investigated the function of PDE10A in SMC proliferation and intimal hyperplasia both in vitro and in vivo.

METHODS AND RESULTS

RT-qPCR, immunoblot, and in situ proximity ligation assay were performed to determine PDE10A expression in synthetic SMCs and injured vessels. We found that PDE10A mRNA and/or protein levels are up-regulated in cultured SMCs upon growth stimulation, as well as in intimal cells in injured mouse femoral arteries. To determine the cellular functions of PDE10A, we focused on its role in SMC proliferation. The anti-mitogenic effects of PDE10A on SMCs were evaluated via cell counting, BrdU incorporation, and flow cytometry. We found that PDE10A deficiency or inhibition arrested the SMC cell cycle at G1-phase with a reduction of cyclin D1. The anti-mitotic effect of PDE10A inhibition was dependent on cGMP-dependent protein kinase Iα (PKGIα), involving C-natriuretic peptide (CNP) and particulate guanylate cyclase natriuretic peptide receptor 2 (NPR2). In addition, the effects of genetic depletion and pharmacological inhibition of PDE10A on neointimal formation were examined in a mouse model of femoral artery wire injury. Both PDE10A knockout and inhibition decreased injury-induced intimal thickening in femoral arteries by at least 50%. Moreover, PDE10A inhibition decreased ex vivo remodelling of cultured human saphenous vein segments.

CONCLUSIONS

Our findings indicate that PDE10A contributes to SMC proliferation and intimal hyperplasia at least partially via antagonizing CNP/NPR2/cGMP/PKG1α signalling and suggest that PDE10A may be a novel drug target for treating vascular occlusive disease.

Modified Natriuretic Peptides and their Potential Role in Cancer Treatment

The natriuretic peptide family (NPs) is a group of natural endocrine hormones, containing a 17-amino acid ring structure connected by disulfide bonds of two cysteines. In this review, the members of the natriuretic peptide family and their corresponding receptors as well as the anti-cancer effects are introduced. Four cardiac hormones of NPs (ANP, VD, KP and LANP) can effectively inhibit the growth of human small cell lung cancer, breast cancer and other tumors and significantly reduce tumor volume in vivo. The in vitro experiments also show that cardiac hormones, CNP and urodilatin can effectively inhibit the growth of most tumor cells. We then further summarized the anti-cancer mechanism of natriuretic peptides. Finally, we introduce several methods that modify natriuretic peptides, leading to enhance their stability and prolong the biological effects of these peptides, which might be helpful for the clinical application in the future. Peptide therapy is a very promising field for cancer treatments since they can induce the death of cancer cells without dramatically affecting normal cells. The synthesis of a useful and stable natriuretic peptide can enhance the effect of cancer treatments and significantly reduce drug resistance and toxicity.

Circulating products of C-type natriuretic peptide and links with organ function in health and disease

Paracrine actions of CNP and rapid degradation at source severely limit study of CNP's many roles in vivo. However provided sensitive and validated assays are used, there is increasing evidence that low concentrations of bioactive CNP in plasma, and the readily detectable concentrations of the bio-inactive processed product of proCNP (aminoterminal proCNP), can be used to advance understanding of the hormone's role in pathophysiology. Provided renal function is normal, concordant changes in both CNP and NTproCNP reflect change in tissue production of proCNP whereas change in CNP alone results from altered rates of bioactive CNP degradation and are reflected in the ratio of NTproCNP to CNP. As already shown in juveniles, where plasma concentration of CNP products are higher and are associated with concurrent endochondral bone growth, measurements of plasma CNP products in mature adults have potential to clarify organ response to stress and injury. Excepting the role of CNP in fetal-maternal welfare, this review examines evidence linking plasma CNP products with function of a wide range of tissues in adults, including the impact of extraneous factors such as nutrients, hormone therapy and exercise.

C-type natriuretic peptide (CNP)/guanylate cyclase B (GC-B) system and endothelin-1(ET-1)/ET receptor A and B system in human vasculature

To assess the physiological and clinical implications of the C-type natriuretic peptide (CNP)/guanylyl cyclase B (GC-B) system in the human vasculature, we have examined gene expressions of CNP and its receptor, GC-B, in human vascular endothelial cells (ECs) and smooth muscle cells (SMCs) and have also compared the endothelin-1(ET-1)/endothelin receptor-A (ETR-A) and endothelin receptor-B (ETR-B) system in human aortic ECs (HAECs) and vascular SMCs (HSMCs) in vitro. We also examined these gene expressions in human embryonic stem (ES)/induced pluripotent stem cell (iPS)-derived ECs and mural cells (MCs). A little but significant amount of mRNA encoding CNP was detected in both human ES-derived ECs and HAECs. A substantial amount of GC-B was expressed in both ECs (iPS-derived ECs and HAECs) and SMCs (iPS-derived MCs and HSMCs). ET-1 was expressed solely in ECs. ETR-A was expressed in SMCs, while ETR-B was expressed in ECs. These results indicate the existence of a vascular CNP/GC-B system in the human vascular wall, indicating the evidence for clinical implication of the CNP/GC-B system in concert with the ET-1/ETR-A and ETR-B system in the human vasculature.

Localization profiles of natriuretic peptides in hearts of pre-hibernating and hibernating Anatolian ground squirrels (Spermophilus xanthoprymnus)

The Anatolian ground squirrel (Spermophilus xanthoprymnus) is a typical example of true mammalian hibernators. In order to adapt to extreme external and internal environments during hibernation, they lower their body temperatures, heart rates and oxygen consumption; however, pathological events such as ischemia and ventricular fibrillation do not occur in their cardiovascular systems. During the hibernation, maintenance of cardiac function is very important for survival of ground squirrels. Natriuretic peptides (NPs) are key factors in the regulation of cardiovascular hemostasis. Since NPs' role on the protection of heart during hibernation are less clear, the aim of this study was to investigate dynamic changes in NPs content in the cardiac chambers and to reveal the possible role of NPs on establishing cardiac function in ground squirrel during hibernation using immunohistochemistry. The immunohistochemical results indicate that cardiac NP expressions in atrial and ventricular cardiomyocytes were different from each other and were sex-independent. ANP and BNP were expressed in a chamber-dependent manner in female and male squirrel hearts. Furthermore, cardiac NPs expression levels in hibernation period were lower than those at the pre-hibernation period. During prehibernation period, ANP, BNP and CNP were expressed in the white and beige adipocytes of epicardial adipose tissue (EAT); while during hibernation period, the brown adipocytes of EAT were positive for BNP and CNP. These data suggest that the hibernation-dependent reduction in levels of NPs, particularly ANP, in cardiac chambers and EAT may be associated with low heart rate and oxygen consumption during hibernation. However, further studies are needed to better delineate the roles of NPs during the hibernation.

Immunolocalization of natriuretic peptides and their receptors in goat (Capra hircus) heart

Natriuretic peptides are structurally similar, but genetically distinct, hormones that participate in cardiovascular homeostasis by regulating blood and extracellular fluid volume and blood pressure. We investigated the distribution of natriuretic peptides and their receptors in goat (Capra hircus) heart tissue using the peroxidase-anti-peroxidase (PAP) immunohistochemical method. Strong staining of atrial natriuretic peptide (ANP) was observed in atrial cardiomyocytes, while strong staining for brain natriuretic peptide (BNP) was observed in ventricular cardiomyocytes. Slightly stronger cytoplasmic C-type natriuretic peptide (CNP) immunostaining was detected in the ventricles compared to the atria. Natriuretic peptide receptor-A (NPR-A) immunoreactivity was more prominent in the atria, while natriuretic peptide receptor-B (NPR-B) immunoreactivity was stronger in the ventricles. Cytoplasmic natriuretic peptide receptor-C (NPR-C) immunoreactivity was observed in both the atria and ventricles, although staining was more prominent in the ventricles. ANP immunoreactivity ranged from weak to strong in endothelial and vascular smooth muscle cells. Endothelial cells exhibited moderate to strong BNP immunoreactivity, while vascular smooth cells displayed weak to strong staining. Endothelial cells exhibited weak to strong cytoplasmic CNP immunoreactivity. Vascular smooth muscle cells were labeled moderately to strongly for CNP. Weak to strong cytoplasmic NPR-A immunoreactivity was found in the endothelial cells and vascular smooth muscle cells stained weakly to moderately for NPR-A. Endothelial and vascular smooth cells exhibited weak to strong cytoplasmic NPR-B immunoreactivity. Moderate to strong NPR-C immunoreactivity was observed in the endothelial and smooth muscle cells. Small gender differences in the immunohistochemical distribution of natriuretic peptides and receptors were observed. Our findings suggest that endothelial cells, vascular smooth cells and cardiomyocytes express both natriuretic peptides and their receptors.

Natriuretic Peptides and Normal Body Fluid Regulation

Natriuretic peptides are structurally related, functionally diverse hormones. Circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are delivered predominantly by the heart. Two C-type natriuretic peptides (CNPs) are paracrine messengers, notably in bone, brain, and vessels. Natriuretic peptides act by binding to the extracellular domains of three receptors, NPR-A, NPR-B, and NPR-C of which the first two are guanylate cyclases. NPR-C is coupled to inhibitory proteins. Atrial wall stress is the major regulator of ANP secretion; however, atrial pressure changes plasma ANP only modestly and transiently, and the relation between plasma ANP and atrial wall tension (or extracellular volume or sodium intake) is weak. Absence and overexpression of ANP-related genes are associated with modest blood pressure changes. ANP augments vascular permeability and reduces vascular contractility, renin and aldosterone secretion, sympathetic nerve activity, and renal tubular sodium transport. Within the physiological range of plasma ANP, the responses to step-up changes are unimpressive; in man, the systemic physiological effects include diminution of renin secretion, aldosterone secretion, and cardiac preload. For BNP, the available evidence does not show that cardiac release to the blood is related to sodium homeostasis or body fluid control. CNPs are not circulating hormones, but primarily paracrine messengers important to ossification, nervous system development, and endothelial function. Normally, natriuretic peptides are not powerful natriuretic/diuretic hormones; common conclusions are not consistently supported by hard data. ANP may provide fine-tuning of reno-cardiovascular relationships, but seems, together with BNP, primarily involved in the regulation of cardiac performance and remodeling. © 2017 American Physiological Society. Compr Physiol 8:1211-1249, 2018.

The multifaceted role of natriuretic peptides in metabolic syndrome

Due to globalization and sophisticated western and sedentary lifestyle, metabolic syndrome has emerged as a serious public health challenge. Obesity is significantly increasing worldwide because of increased high calorie food intake and decreased physical activity leading to hypertension, dyslipidemia, atherosclerosis, and insulin resistance. Thus, metabolic syndrome constitutes cardiovascular disease, type 2 diabetes, obesity, and nonalcoholic fatty liver disease (NAFLD) and recently some cancers are also considered to be associated with this syndrome. There is increasing evidence of the involvement of natriuretic peptides (NP) in the pathophysiology of metabolic diseases. The natriuretic peptides are cardiac hormones, which are produced in the cardiac atrium, ventricles of the heart and the endothelium. These peptides are involved in the homeostatic control of body water, sodium intake, potassium transport, lipolysis in adipocytes and regulates blood pressure. The three known natriuretic peptide hormones present in the natriuretic system are atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and c-type natriuretic peptide (CNP). These three peptides primarily function as endogenous ligands and mainly act via their membrane receptors such as natriuretic peptide receptor A (NPR-A), natriuretic peptide receptor B (NPR-B) and natriuretic peptide receptor C (NPR-C) and regulate various physiological and metabolic functions. This review will shed light on the structure and function of natriuretic peptides and their receptors and their role in the metabolic syndrome.

Associations Between Genetic Variants of the Natriuretic Peptide System and Blood Pressure Response to Dietary Sodium Intervention: The GenSalt Study

BACKGROUND

The aim of this study was to comprehensively test the association of genetic variants in the natriuretic peptide (NP) system with blood pressure (BP) response to dietary sodium intervention in a Chinese population.

METHODS

We conducted a 7-day low-sodium intervention followed by a 7-day high-sodium intervention among 1,906 participants in rural China. BP measurements were obtained at baseline and each dietary intervention using a random-zero sphygmomanometer. Linear mixed-effect models were used to assess the associations of 48 single-nucleotide polymorphisms (SNPs) in 6 genes of NP system with BP response to dietary sodium intervention.

RESULTS

SNP rs5063 in the NPPA gene and SNP rs2077386 in the NPPC gene exhibited significant associations with BP response to low-sodium dietary intervention under recessive genetic model. For rs5063, absolute mean arterial pressure responses (95% confidence interval) to the low-sodium intervention were 1.31 (-1.08, 3.70) mm Hg for TT genotype and -3.74 (-4.01, -3.46) mm Hg for CC or TC genotype, respectively (P = 4.1 × 10(-5)). Individuals with at least one copy of the C allele of rs2077386 had significantly reduction in systolic BP during the low-sodium intervention compared to those with genotype GG with responses of -5.48 (-5.83, -5.14) vs. -2.76 (-3.52, -2.00) mm Hg, respectively (P = 1.9 × 10(-13)).

CONCLUSIONS

These novel findings suggested that genetic variants of NP system may contribute to the variation of BP response to sodium intervention in Chinese population. Certainly, replication of these results in other populations and further functional studies are warranted to clarify their role in the regulation of BP and hypertension.

C-type natriuretic peptide: a new cardiac mediator

Natriuretic peptides are endogenous hormones released by the heart in response to myocardial stretch and overload. While atrial and brain natriuretic peptides (ANP, BNP) were immediately considered cardiac hormones and their role was well-characterized and defined in predicting risk in cardiovascular disease, evidence indicating the role of C-type natriuretic peptide (CNP) in cardiovascular regulation was slow to emerge until about 8 years ago. Since then, considerable literature on CNP and the cardiovascular system has been published; the aim of this review is to examine current literature relating to CNP and cardiovascular disease, in particular its role in heart failure (HF) and myocardial infarction (MI). This review retraces the fundamental steps in research that led understanding the role of CNP in HF and MI; from increased CNP mRNA expression and plasmatic concentrations in humans and in animal models, to detection of CNP expression in cardiomyocytes, to its evaluation in human leukocytes. The traditional view of CNP as an endothelial peptide has been surpassed by the results of many studies published in recent years, and while its physiological role is still under investigation, information is now available regarding its contribution to cardiovascular function. Taken together, these observations suggest that CNP and its specific receptor, NPR-B, can play a very important role in regulating cardiac hypertrophy and remodeling, indicating NPR-B as a new potential drug target for the treatment of cardiovascular disease.

Overexpressed C-type natriuretic peptide serves as an early compensatory response to counteract extracellular matrix remodeling in unilateral ureteral obstruction rats

Although the mechanism underlying C-type natriuretic peptide (CNP) beneficial effects is not entirely understood, modulating the expression of matrix metalloproteinases (MMPs)/tissue inhibitors of metalloproteinases (TIMPs) may play an important role. The study presented herein was designed as a first demonstration of the regulative effects of CNP on MMPs/TIMPs expression in unilateral ureteral obstruction (UUO) rats. The continuous changes of CNP, MMP-2, MMP-9, TIMP-1, TIMP-2 and type IV collagen (Col-IV) expression were determined in the obstructed rat kidneys at 3 days, 1, 2, and 3 months post-UUO respectively. According to the real-time PCR analysis, CNP, MMP-2 and MMP-9 mRNA expression in the obstructed kidneys were significantly higher compared to every time corresponding SOR, and progressively decreased over time. In contrast, in the obstructed kidneys collected 2 and 3 months post-UUO, the higher TIMP-1 and TIMP-2 mRNA expression were observed in comparison to the corresponding SOR group. The above trends of CNP, MMP-2, MMP-9, TIMP-1, and TIMP-2 transcripts were confirmed by their protein expression based on immunohistochemistry and western blot, and finally contributed to the progressive elevated Col-IV expression in the obstructed kidneys throughout the entire study period. Overexpressed CNP may be an early compensatory response to counteract extracellular matrix remodeling in UUO rats.

Use of cardiac biomarkers in neonatology

Cardiac biomarkers are used to identify cardiac disease in term and preterm infants. This review discusses the roles of natriuretic peptides and cardiac troponins. Natriuretic peptide levels are elevated during atrial strain (atrial natriuretic peptide (ANP)) or ventricular strain (B-type natriuretic peptide (BNP)). These markers correspond well with cardiac function and can be used to identify cardiac disease. Cardiac troponins are used to assess cardiomyocyte compromise. Affected cardiomyocytes release troponin into the bloodstream, resulting in elevated levels of cardiac troponin. Cardiac biomarkers are being increasingly incorporated into clinical trials as indicators of myocardial strain. Furthermore, cardiac biomarkers can possibly be used to guide therapy and improve outcome. Natriuretic peptides and cardiac troponins are potential tools in the diagnosis and treatment of neonatal disease that is complicated by circulatory compromise. However, clear reference ranges need to be set and validation needs to be carried out in a population of interest.

Regulation of C-type natriuretic peptide expression

C-type natriuretic peptide (CNP) is a member of the small family of natriuretic peptides that also includes atrial natriuretic peptide (ANP) and brain, or B-type natriuretic peptide (BNP). Unlike them, it performs its major functions in an autocrine or paracrine manner. Those functions, mediated through binding to the membrane guanylyl cyclase natriuretic peptide receptor B (NPR-B), or by signaling through the non-enzyme natriuretic peptide receptor C (NPR-C), include the regulation of endochondral ossification, reproduction, nervous system development, and the maintenance of cardiovascular health. To date, the regulation of CNP gene expression has not received the attention that has been paid to regulation of the ANP and BNP genes. CNP expression in vitro is regulated by TGF-β and receptor tyrosine kinase growth factors in a cell/tissue-specific and sometimes species-specific manner. Expression of CNP in vivo is altered in diseased organs and tissues, including atherosclerotic vessels, and the myocardium of failing hearts. Analysis of the human CNP gene has led to the identification of a number of regulatory sites in the proximal promoter, including a GC-rich region approximately 50 base pairs downstream of the Tata box, and shown to be a binding site for several putative regulatory proteins, including transforming growth factor clone 22 domain 1 (TSC22D1) and a serine threonine kinase (STK16). The purpose of this review is to summarize the current literature on the regulation of CNP expression, emphasizing in particular the putative regulatory elements in the CNP gene and the potential DNA-binding proteins that associate with them.

Expression of C-type natriuretic peptide and its receptor NPR-B in cardiomyocytes

C-type natriuretic peptide (CNP) was recently found in myocardium at the mRNA and protein levels, but it is not known whether cardiomyocytes are able to produce CNP. The aim of this study was to determine the expression of CNP and its specific receptor NPR-B in cardiac cells, both in vitro and ex vivo. CNP, brain natriuretic peptide (BNP) and natriuretic peptide receptor (NPR)-B mRNA expression were examined by RT-PCR in the H9c2 rat cardiac myoblast cell line, in neonatal rat primary cardiomyocytes and in human umbilical vein endothelial cells (HUVECs) as control. CNP protein expression was probed in cardiac tissue sections obtained from adult male minipigs by immunohistochemistry, and in H9c2 cells both by immunocytochemistry and by specific radioimmunoassay. The results showed that cardiac cells as well as endothelial cells were able to produce CNP. Unlike cardiomyocytes, as expected, in endothelial cells expression of BNP was not detected. NPR-B mRNA expression was found in both cell types. Production of CNP in the heart muscle cells at protein level was confirmed by radioimmunological determination (H9c2: CNP=0.86 ± 0.083 pg/mg) and by immunocytochemistry studies. By immunostaining of tissue sections, CNP was detected in both endothelium and cardiomyocytes. Expression of CNP in cardiac cells at gene and protein levels suggests that the heart is actively involved in the production of CNP.

The response of non-traditional natriuretic peptide production sites to salt and water manipulations in the rainbow trout

Natriuretic peptides (NPs) and their receptors (NPRs) comprise an evolutionarily conserved signaling system with profound physiological effects on vertebrate renal and cardiovascular systems. Some NPs (ANP, BNP and VNP)are primarily of cardiac origin whereas CNP is common in the brain. In mammals, non-traditional sites of NPs synthesis, BNP in brain and CNP in atrium, appear to have complementary actions. In the present study, trout were chronically adapted to freshwater (FW) (a volume-loading, salt-depleting environment), saltwater (SW) (a volume-depleting, salt-loading environment),FW and fed a high-salt diet (FW–HSD) (a volume- and salt-loading regime)or acutely volume depleted or expanded by hemorrhage or infusion with dialyzed plasma to perturb volume homeostasis. The responses of brain and atrial BNP and CNP mRNA, pro-peptide, NPR-A and NPR-B were evaluated using quantitative PCR and western analysis. Brain pro-BNP and NPR-A was increased in FW–HSD trout and decreased in SW trout. Brain pro-CNP was largely unaffected whereas NPR-B mRNA was increased in FW–HSD trout. Atrial CNP,although produced at lower levels than other cardiac NPs, was markedly elevated in chronically (FW–HSD) and acutely volume expanded trout(dialyzed-plasma infusion) whereas decreased in hemorrhaged trout. These findings indicate that non-traditional NP synthesis sites in the trout probably complement the broad hypovolemic and hypotensive actions of traditional (cardiac) NP synthesis sites in response to volume expansion but not to plasma osmolarity. This supports the hypothesis that the piscine and mammalian NP systems are fundamentally similar and appear to protect the heart from volume overload.

Differential protein expression in heart in UT-B null mice with cardiac conduction defects

Cardiac conduction defects were found in transgenic mice deficient in urea transporter UT-B. To investigate the molecular mechanisms of the conduction defects caused by UT-B deletion, we studied the protein expression profiles of heart tissue (comprising most conduction system) in wild-type versus UT-B null mice at different ages. By two-dimensional electrophoresis-based comparative analysis, we found that more than dozen proteins were modulated (>two-fold) in the myocardium of UT-B null mice. Out of these modulated proteins, troponin T (TNNT2) presented significant changes in UT-B null mice at early stage prior to the development of P-R interval elongation, while the change of atrial natriuretic peptide (ANP) occurred only at late stage in UT-B null mice that had the AV block. These data indicate that UT-B deletion caused the dynamic expression regulation of TNNT2 and ANP, and these proteins may provide new clues to investigate the molecular events involved in cardiac conduction.

Natriuretic peptides in vascular physiology and pathology

Four major natriuretic peptides have been isolated: atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), and Dendroaspis-type natriuretic peptide (DNP). Natriuretic peptides play an important role in the regulation of cardiovascular homeostasis maintaining blood pressure and extracellular fluid volume. The classical endocrine effects of natriuretic peptides to modulate fluid and electrolyte balance and vascular smooth muscle tone are complemented by autocrine and paracrine actions that include regulation of coronary blood flow and, therefore, myocardial perfusion; modulation of proliferative responses during myocardial and vascular remodeling; and cytoprotective anti-ischemic effects. The actions of natriuretic peptides are mediated by the specific binding of these peptides to three cell surface receptors: type A natriuretic peptide receptor (NPR-A), type B natriuretic peptide receptor (NPR-B), and type C natriuretic peptide receptor (NPR-C). NPR-A and NPR-B are guanylyl cyclase receptors that increase intracellular cGMP concentration and activate cGMP-dependent protein kinases. NPR-C has been presented as a clearance receptor and its activation also results in inhibition of adenylyl cyclase activity. The wide range of effects of natriuretic peptides might be the base for the development of new therapeutic strategies of great benefit in patients with cardiovascular problems including coronary artery disease or heart failure. This review summarizes current literature concerning natriuretic peptides, their receptors and their effects on fluid/electrolyte balance, and vascular and cardiac physiology and pathology, including primary hypertension and myocardial infarction. In addition, we will attempt to provide an update on important issues regarding natriuretic peptides in congestive heart failure.

Recent advances in natriuretic peptide research

The natriuretic peptides are a family of related hormones that play a crucial role in cardiovascular and renal homeostasis. They have recently emerged as potentially important clinical biomarkers in heart failure. Natriuretic peptides, particularly brain natriuretic peptide (BNP) and the inactive N-terminal fragment of BNP, NT-proBNP, that has an even greater half-life than BNP, are elevated in heart failure and therefore considered to be excellent predictors of disease outcome. Nesiritide, a recombinant human BNP, has been shown to provide symptomatic and haemodynamic improvement in acute decompensated heart failure, although recent reports have suggested an increased short-term risk of death with nesiritide use. This review article describes: the current use of BNP and its inactive precursor NT-proBNP in diagnosis, screening, prognosis and monitoring of therapy for congestive heart failure, the renoprotective actions of natriuretic peptides after renal failure and the controversy around the therapeutic use of the recombinant human BNP nesiritide.

Treatment of streptozotocin-induced diabetic rats with AVE7688, a vasopeptidase inhibitor: effect on vascular and neural disease

In epineurial arterioles, acetylcholine-mediated vascular relaxation is mediated by nitric oxide and endothelium-derived hyperpolarizing factor (EDHF), and both mechanisms are impaired by diabetes. The mediator responsible for the effect of EDHF is unknown. In epineurial arterioles, C-type natriuretic peptide (CNP) has properties consistent with EDHF-like activity. Epineurial arterioles express CNP, and exogenous CNP causes a concentration-dependent vascular relaxation. In streptozotocin-induced diabetic rats, CNP-mediated vascular relaxation in epineurial arterioles is decreased. Since CNP may be a regulator of vascular function, a vasopeptidase inhibitor may be an effective treatment for diabetes-induced vascular and neural disease. Vasopeptidase inhibitors inhibit ACE activity and neutral endopeptidase, which degrades natriuretic peptides. Streptozotocin-induced diabetic rats were treated with AVE7688 (450 mg/kg in the diet), a vasopeptidase inhibitor, for 8-10 weeks after 4 weeks of untreated diabetes. Treatment of diabetic rats corrected the diabetes-induced decrease in endoneurial blood flow, significantly improved motor and sensory nerve conduction velocity, prevented the development of hypoalgesia in the hind paw, and reduced superoxide and nitrotyrosine levels in epineurial arterioles. The diabetes-induced decrease in acetylcholine-mediated vascular relaxation by epineurial arterioles was significantly improved with treatment. These studies suggest that vasopeptidase inhibitors may be an effective approach for the treatment of diabetic vascular and neural dysfunction.

Increase of C-type natriuretic peptide expression by serum and platelet-derived growth factor-BB in human aortic smooth muscle cells is dependent on protein kinase C activation

C-type natriuretic peptide (CNP) is produced by the vascular smooth muscle cells (SMCs) of injured and atherosclerotic arteries, in which it may exert autocrine control over SMCs by binding to its principal receptors, NPR-B and NPR-C, but few studies have examined the factors that regulate CNP expression in human SMCs. In the present report, we show that serum induces significant increases in both CNP and NPR-C transcript levels in human, but not rat SMCs in culture, and that pretreatment with either the general tyrosine kinase inhibitor genistein, the platelet-derived growth factor (PDGF) tyrosine kinase inhibitor AG 1296, or the protein kinase C (PKC) inhibitor GF109203X blocks most of the serum-induced increase in CNP. PDGF-BB also induced significant dose-dependent increases in CNP transcript that correlated temporally with the serum effect on CNP mRNA. Inhibition of several PDGF-BB signaling pathways downstream of receptor activation showed that PKC inhibition with GF109203X was almost as effective as genistein in abolishing the PDGF-BB-induced up-regulation of CNP mRNA. Furthermore, PKC activation by phorbol 12-myristate 13-acetate (PMA) produced an extremely high level of CNP mRNA that was abolished by GF109203X. Immunoreactive CNP was markedly increased in SMCs receiving 10% serum, 20 ng/ml PDGF-BB, or PMA, and was decreased in PDGF-treated and PMA-treated cells by AG 1296 and GF109203X, respectively. This report suggests that in humans, PDGF and other factors signaling through receptor tyrosine kinases and downstream activation of PKC could represent an important control for CNP expression in vascular smooth muscle.

The presence of ANP in rat peritoneal mast cells

Atrial natriuretic peptide (ANP) is an important component of the natriuretic peptide system. A great role in many regulatory systems is played by mast cells. Meanwhile involvement of these cells in ANP activity is poorly studied. In this work, we have shown the presence of ANP in rat peritoneal mast cells. Pure fraction of mast cells was obtained by separation of rat peritoneal cells on a Percoll density gradient. By Western blotting, two ANP-immunoreactive proteins of molecular masses of 2.5 kDa and 16.9 kDa were detected in lysates from these mast cells. Electron microscope immunogold labeling has revealed the presence of ANP-immunoreactive material in storage, secreting and released granules of mast cells. Our findings indicate the rat peritoneal mast cells to contain both ANP prohormone and ANP. These both peptides are located in mast cell secretory granules and released by mechanism of degranulation. It is discussed that many mast cell functions might be due to production of natriuretic peptides by these cells.

Gene expression, secretion, and autocrine action of C-type natriuretic peptide in cultured adult rat cardiac fibroblasts

C-type natriuretic peptide (CNP), the third member of the natriuretic peptide family, is known to be synthesized in the central nervous system and vascular endothelial cells, in contrast to atrial natriuretic peptide and brain natriuretic peptide. However, there have been no studies concerning CNP production in cultured cardiac cells. Here, we examined the production and the local effect of CNP in cultured ventricular cells. Under serum-free conditions, adult rat cardiac fibroblasts secreted immunoreactive CNP time dependently. TGF-beta1, basic fibroblast growth factor, and endothelin-1 significantly stimulated CNP secretion. Northern blot analysis detected significant expressions of CNP and its specific receptor (guanylyl cyclase-B) mRNA in cardiac fibroblasts. CNP stimulated intracellular cGMP production in fibroblasts more intensely than atrial and brain natriuretic peptides. CNP inhibited both DNA and collagen syntheses of cardiac fibroblasts, and these inhibitory effects by CNP were stronger than by atrial and brain natriuretic peptides. The inhibition by CNP of DNA and collagen syntheses was reproduced by a cGMP analog, 8-bromo cGMP. The present findings demonstrate that CNP is synthesized in and secreted from cardiac fibroblasts and suggest that CNP has a suppressive effect on fibroblast proliferation and extracellular matrix production, probably via the guanylyl cyclase-B-mediated cGMP-dependent process. CNP produced by cardiac fibroblasts may play a role as an autocrine regulator against excessive cardiac fibrosis.

Comparative study in the effect of C-type natriuretic peptide on gastric motility in various animals

AIM

To investigate the effect of natriuretic peptides on gastric motility in various animals, and the effect of C-type natriuretic peptide (CNP) on spontaneous contraction of gastric smooth muscle in rat, guinea-pig and human in vitro was compared.

METHODS

Spontaneous contraction of gastric smooth muscle was recorded by four channel physiograph.

RESULTS

In the guinea-pig and rat gastric antral circular smooth muscle, CNP markedly decreased the amplitude of spontaneous contraction but it didn't affect the frequency, however, the contractile activity was completely inhibited by CNP in gastric antral longitudinal smooth muscle. In the human gastric antral circular and longitudinal smooth musle, CNP completely inhibited spontaneous contraction. In the circular smooth muscle of guinea-pig and rat gastric fundus, CNP obviously decreased the amplitude of spontaneous contraction but it didn't affect the frequency, however, the contractile activity was completely inhibited by CNP in smooth muscle of fundus longitudinal. In the circular and longitudinal smooth muscle of guinea-pig gastric body, CNP at first induced a relaxation and then an increase in amplitude of spontaneous contraction (rebound contraction), but the frequency was not changed. After the circular smooth muscle of gastric body was pretreated with atropine, an M receptor blocker, the rebound contraction was abolished; In circular and longitudinal smooth muscle of rat gastric body, CNP induced a transient and slight relaxation and successively followed by the recovery in amplitude of spontaneous contraction but it also didn't affect the frequency. After the smooth muscle was pretreated with atropine, the transient and slight relaxation was replaced by long term and complete inhibition; The percentage of CNP-induced inhibition was 76.77+/-6.21 % (fundus), 67.21+/-5.32 % (body) and 58.23+/- 6.21 % (antral) in the gastric circular muscle, however, the inhibitory percentage was 100+/-0.00 % (fundus), 68.66+/- 3.55 % (body) and 100+/-0.00 % (antrum) in the gastric longitudinal smooth muscle of guinea-pigs; In the rat, the percentage of CNP-induced inhibition was 95.87+/-4.12 % (fundus), 94.91+/-5.08 % (body) and 66.32+/-7.32 % (antrum)in the gastric circular smooth muscle, but in the longitudinal smooth muscle, CNP completely inhibited the spontaneous contraction. Using LY83583, a guanylate cyclase inhibitor, and zaparinast as a phosphoesterase inhibitor to inhibit the generation of cGMP, the effect of CNP on the spontaneous contraction was markedly weakened by LY83583, however, the inhibitory effect was enhanced by zaparinast.

CONCLUSION

(1) CNP can obviously inhibit the spontaneous contraction of gastric antral circular and longitudinal smooth muscle in the rat, guinea-pig and human. The order of inhibitory potency is human >rat> guinea-pig. (2) In the same animals, the inhibitory effect of CNP on spontaneous contraction is the most powerful in fundus and the weakest in antrum, in the same position, the inhibitory effect on the circular smooth muscle is more powerful than that on longitudinal smooth muscle. (3) The inhibitory effect of CNP on spontaneous contraction in the gastric smooth muscle is mediated by a cGMP dependent pathway.