Cardiac natriuretic peptides.

Investigations into the mixed muscle-secretory phenotype of cardiomyocytes from the atrial appendages of the heart led to the discovery that these cells produce, in a regulated manner, two polypeptide hormones - the natriuretic peptides - referred to as atrial natriuretic factor or atrial natriuretic peptide (ANP) and brain or B-type natriuretic peptide (BNP), thereby demonstrating an endocrine function for the heart. Studies on the gene encoding ANP (NPPA) initiated the field of modern research into gene regulation in the cardiovascular system. Additionally, ANP and BNP were found to be the natural ligands for cell membrane-bound guanylyl cyclase receptors that mediate the effects of natriuretic peptides through the generation of intracellular cGMP, which interacts with specific enzymes and ion channels. Natriuretic peptides have many physiological actions and participate in numerous pathophysiological processes. Important clinical entities associated with natriuretic peptide research include heart failure, obesity and systemic hypertension. Plasma levels of natriuretic peptides have proven to be powerful diagnostic and prognostic biomarkers of heart disease. Development of pharmacological agents that are based on natriuretic peptides is an area of active research, with vast potential benefits for the treatment of cardiovascular disease.

Techniques for the Evaluation of the Genetic Expression, Intracellular Storage, and Secretion of Polypeptide Hormones with Special Reference to the Natriuretic Peptides (NPs).

Techniques developed over the years in our laboratory for the study of tissue expression, storage, and secretion of the cardiac hormones ANF, BNP, and CNP are described below. They have proven highly reliable in our hands when the steps outlined are followed as described. Given the generic nature of the procedures, these should be applicable to other polypeptides.

The heart as an endocrine organ.

The concept of the heart as an endocrine organ arises from the observation that the atrial cardiomyocytes in the mammalian heart display a phenotype that is partly that of endocrine cells. Investigations carried out between 1971 and 1983 characterised, by virtue of its natriuretic properties, a polypeptide referred to atrial natriuretic factor (ANF). Another polypeptide isolated from brain in 1988, brain natriuretic peptide (BNP), was subsequently characterised as a second hormone produced by the mammalian heart atria. These peptides were associated with the maintenance of extracellular fluid volume and blood pressure. Later work demonstrated a plethora of other properties for ANF and BNP, now designated cardiac natriuretic peptides (cNPs). In addition to the cNPs, other polypeptide hormones are expressed in the heart that likely act upon the myocardium in a paracrine or autocrine fashion. These include the C-type natriuretic peptide, adrenomedullin, proadrenomedullin N-terminal peptide and endothelin-1. Expression and secretion of ANF and BNP are increased in various cardiovascular pathologies and their levels in blood are used in the diagnosis and prognosis of cardiovascular disease. In addition, therapeutic uses for these peptides or related substances have been found. In all, the discovery of the endocrine heart provided a shift from the classical functional paradigm of the heart that regarded this organ solely as a blood pump to one that regards this organ as self-regulating its workload humorally and that also influences the function of several other organs that control cardiovascular function.

[The endocrine heart and inflammation]. / El corazón endocrino y el proceso inflamatorio.

The endocrine heart produces the polypeptide hormones Atrial Natriuretic Factor (ANF or ANP) and Brain Natriuretic Peptide (BNP). Through the peripheral actions of these hormones the heart contributes to the regulation of the cardiac preload and afterload. More recently, new functions for these hormones have been described including the modulation of the immune response. Plasma levels of BNP but not those of ANF, increase following an acute rejection episode of a cardiac allotransplant but return to levels pre-rejection with successful treatment. This observation constitutes the first observation leading to characterizing the interactions of BNP with the immune response. Several other pathologies with an inflammatory component are now known to be associated with an increase in the production of BNP. Such an increase is due to an increase in the transcriptional activity of the BNP gene induced by cytokines and related substances. In vitro investigations have shown that an increase in BNP directly modulates immunological activity. Inflammation and hemodynamic changes co-exist in several cardiovascular diseases and therefore it may be beneficial to measure circulating levels of both ANF and BNP as biomarkers of changes in intravascular volume and of changes in intravascular volume plus inflammation, respectively. Changes in plasma ANF, that are relatively larger than those of BNP, might be an indication of hemodynamic deterioration while important changes in circulating BNP could indicate a worsening of the inflammatory process.

El corazón endocrino y el proceso inflamatorio / [The endocrine heart and inflammation].

The endocrine heart produces the polypeptide hormones Atrial Natriuretic Factor (ANF or ANP) and Brain Natriuretic Peptide (BNP). Through the peripheral actions of these hormones the heart contributes to the regulation of the cardiac preload and afterload. More recently, new functions for these hormones have been described including the modulation of the immune response. Plasma levels of BNP but not those of ANF, increase following an acute rejection episode of a cardiac allotransplant but return to levels pre-rejection with successful treatment. This observation constitutes the first observation leading to characterizing the interactions of BNP with the immune response. Several other pathologies with an inflammatory component are now known to be associated with an increase in the production of BNP. Such an increase is due to an increase in the transcriptional activity of the BNP gene induced by cytokines and related substances. In vitro investigations have shown that an increase in BNP directly modulates immunological activity. Inflammation and hemodynamic changes co-exist in several cardiovascular diseases and therefore it may be beneficial to measure circulating levels of both ANF and BNP as biomarkers of changes in intravascular volume and of changes in intravascular volume plus inflammation, respectively. Changes in plasma ANF, that are relatively larger than those of BNP, might be an indication of hemodynamic deterioration while important changes in circulating BNP could indicate a worsening of the inflammatory process.

Brain natriuretic Peptide production and secretion in inflammation.

Gene expression and secretion of the cardiac polypeptide hormones atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) are simultaneously upregulated in various cardiac disorders such as congestive heart failure, ischemic heart disease, and hypertensive heart disease, in which hemodynamic or neuroendocrine changes are key components in the progression of disease. However, during acute cardiac allograft rejection, plasma BNP levels are increased but not those of ANF. Successful treatment of the rejection episode decreases the elevated plasma BNP to prerejection values suggesting that substances related to inflammation may selectively influence BNP gene expression. Indeed, cytokines such as TNFα and IL-1ß selectively stimulate cardiac BNP at the transcriptional and translational levels in cardiomyocyte cultures without affecting ANF. This selective BNP increase is seen in vivo, in addition to acute cardiac allograft rejection, in several circumstances where inflammation significantly contributes to the pathogenesis of disease such as in sepsis and in acute myocarditis.

Thirty years of research on atrial natriuretic factor: historical background and emerging concepts.

The discovery of the natriuretic properties of atrial muscle extracts pointed to the existence of an endocrine function of the heart that is now known to be mediated by the polypeptide hormones atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP). On the basis of such a finding, approximately 27 000 publications to date have described a wide variety of biological properties of the heart hormones as well as their application as therapeutic agents and biomarkers of cardiac disease. Stimulation of secretion of ANF and BNP from the atria is mediated through mechanisms involving G proteins of the G(q) or G(o) types. We showed that the latter type underlies the transduction of muscle stretch into stimulated secretion and that it is more highly abundant in atria than in ventricles. The Gα(o)()-1 subunit appears to play a key role in the biogenesis of atrial granules and in the intracellular targeting of their contents. Protein interaction studies using a yeast two-hybrid approach showed interactions between Gα(o)()-1, proANF, and the intermediate conductance, calcium-activated K(+) channel SK4. Pharmacological inhibition of this channel decreases ANF secretion. Unpublished studies using in vitro knockdowns suggest interdependency in granule protein expression levels. These studies suggest previously unknown mechanisms of intracellular targeting and secretion control of the heart hormones that may find an application in the therapeutic manipulation of circulating ANF and BNP.

Cardiac hormones ANF and BNP modulate proliferation in the unidirectional mixed lymphocyte reaction.

BACKGROUND: Previous investigations have shown that the plasma levels of the cardiac hormone brain natriuretic peptide (BNP) increase during acute cardiac allograft rejection as diagnosed by endomyocardial biopsy. Successful immunosuppressant treatment decreased plasma BNP levels, suggesting a role for BNP in transplantation immunity. We tested a possible immunomodulatory effect of the natriuretic peptides (NPs) BNP, atrial natriuretic factor (ANF), and C-type NP (CNP) using the unidirectional mixed lymphocyte reaction (MLR). METHODS: Lymphocytes were isolated from the lymph nodes of Brown Norway (BN) and Lewis (L) rats. BN lymphocytes were gamma-irradiated to inhibit DNA synthesis. Lymphocytes at 2.5 x 10(6) cell/ml were mixed (at an L:BN ratio of 4:1) and incubated. On Days 2 and 3, ANF (10(-6) to 10(-11) mol/liter), BNP (10(-5) to 10(-11) mol/liter), or CNP (10(-6) to 10(-12) mol/liter) were added. Cell proliferation was measured on Day 4. RESULTS: Reverse transcript-polymerase chain reaction (RT-PCR) analysis of BN and L lymphocytes detected NP receptor (NPR) mRNA amplicons of the expected size. MLR induced an increase in relative receptor abundance as follows: NPRA > NPRB > NPRC. ANF and BNP significantly inhibited up to approximately 50% lymphocyte proliferation in a dose-dependent manner in the range of 10(-11) to 10(-6) mol/liter, whereas CNP significantly decreased lymphocyte proliferation only modestly (approximately 20%) at 10(-8) mol/liter and at 10(-6) mol/liter. CONCLUSIONS: Both ANF and BNP have immunomodulatory functions, although the response to cardiac rejection observed clinically involves increases in plasma levels of BNP only. This is likely related to BNP gene promoter sequences previously reported to be responsive to specific cytokines and related substances. The modulation of the MLR by NP suggests a possible clinical use of these peptides in transplantation immunity.

Transcriptional analysis of the mammalian heart with special reference to its endocrine function.

BACKGROUND: Pharmacological and gene ablation studies have demonstrated the crucial role of the endocrine function of the heart as mediated by the polypeptide hormones ANF and BNP in the maintenance of cardiovascular homeostasis. The importance of these studies lies on the fact that hypertension and chronic congestive heart failure are clinical entities that may be regarded as states of relative deficiency of ANF and BNP. These hormones are produced by the atrial muscle cells (cardiocytes), which display a dual secretory/muscle phenotype. In contrast, ventricular cardiocytes display mainly a muscle phenotype. Comparatively little information is available regarding the genetic background for this important phenotypic difference with particular reference to the endocrine function of the heart. We postulated that comparison of gene expression profiles between atrial and ventricular muscles would help identify gene transcripts that underlie the phenotypic differences associated with the endocrine function of the heart. RESULTS: Comparison of gene expression profiles in the rat heart revealed a total of 1415 differentially expressed genes between the atria and ventricles based on a 1.8 fold cut-off. The identification of numerous chamber specific transcripts, such as ANF for the atria and Irx4 for the ventricles among several others, support the soundness of the GeneChip data and demonstrates that the differences in gene expression profiles observed between the atrial and ventricular tissues were not spurious in nature. Pathway analysis revealed unique expression profiles in the atria for G protein signaling that included Galphao1, Ggamma2 and Ggamma3, AGS1, RGS2, and RGS6 and the related K+ channels GIRK1 and GIRK4. Transcripts involved in vesicle trafficking, hormone secretion as well as mechanosensors (e.g. the potassium channel TREK-1) were identified in relationship to the synthesis, storage and secretion of hormones. CONCLUSION: The data developed in this investigation describes for the first time data on gene expression particularly centred on the secretory function of the heart. This provides for a rational approach in the investigation of determinants of the endocrine of the heart in health and disease.

Cardiac natriuretic peptides gene expression and secretion in inflammation.

The genetic expression and secretion of the cardiac polypeptide hormones atrial natriuretic factor (ANF or ANP) and brain natriuretic peptide (BNP) have been studied mainly in the context of cardiac diseases associated with neuroendocrine and hemodynamic changes arising from cardiac dysfunction such as in chronic congestive heart failure. In this type of pathology, both ANF and BNP plasma levels change in an approximate coordinated fashion so that the use of these hormones as biomarkers of cardiac disease is, in principle, indistinctive. However, we reported that during an acute cardiac allograft rejection episode, BNP plasma levels can significantly increase in the absence of a similar increase in ANF plasma levels. We tested the hypothesis that these changes were related to cytokines and found that some pro-inflammatory cytokines, including TNFalpha and IL-1beta, selectively promote BNP synthesis and secretion in cultures of neonatal rat ventricular cardiocytes. This effect was found related to increased BNP promoter activity and sensitive to p38 mitogen-activated protein kinase inhibition.In order to determine in vivo if the selective up-regulation of BNP would be observed in inflammatory processes other than acute cardiac allograft rejection, we carried out investigation using the experimental autoimmune myocarditis rat model, which histologically resembles human giant cell myocarditis. It was found that this model is also accompanied by a specific increase in BNP-circulating levels although the cytokines involved seem to differ from those characterized earlier through in vitro studies.Recent studies in humans have found that in sepsis, plasma BNP levels increase in the absence of hemodynamic changes.In conclusion, BNP appears to be regulated uniquely in the setting of an inflammatory process. This sets it apart from ANF in terms of potential roles in the pathogenesis of disease and in its use as a biomarker of cardiac disease.

Role of potassium channels in stretch-promoted atrial natriuretic factor secretion.

The cardiac polypeptide hormone atrial natriuretic factor (ANF) plays important roles in the regulation of blood volume and pressure. Few specific details are known about basal or stretch-promoted ANF secretion. Here, we investigated the involvement of K(+) channels in ANF secretion based on investigations of their nature as revealed by oligonucleotide microarray analysis and on protein-protein interactions evidenced by a yeast two-hybrid approach using a heterotrimeric Galphao-1 G protein subunit, which is particularly abundant in the atrium. Based on these data, we investigated the effect of drugs known to pharmacologically affect the function of specific K(+) channels on ANF secretion from the isolated rat atrium. These included adenosine triphosphate-sensitive K(+) channels, TWIK-related K(+) channel 1 (TREK-1), and the Ca(+2)-activated intermediate conductance K(+) channel (SK4). The sulfonylurea ligands tolbutamide and repaglinide, but not glibenclamide, increased stretch-promoted ANF secretion. The channel openers diazoxide, pinacidil, and cromakalim all decreased this type of stimulated ANF secretion. TRAM 34, a specific SK4 inhibitor, and oleylamine, a nonspecific TREK-1 inhibitor, significantly decreased or increased respectively, both basal and stretch-stimulated ANF secretion. Inhibition of Gi/o by pretreatment with Pertussis toxin often significantly affected the effect of these treatments. We concluded that the atria express K(+) channels that are related to Gi/o protein signaling and that significantly affect the endocrine function of the heart. These findings are significant for the development of therapeutic drugs with properties related to the manipulation of ANF plasma levels.

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.

Determinants of natriuretic peptide production by the heart: basic and clinical implications.

The cardiac natriuretic peptides (NPs) atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) are polypeptide hormones synthesized, stored, and secreted by cardiac muscle cells (cardiocytes). The NPs modulate extracellular fluid volume and blood pressure and have potent growth-regulating properties, which make them of great interest for cardiac remodeling in acute myocardial infarction and congestive heart failure. We have observed that the production of NP can be coordinately or discoordinately regulated. In the former type, muscle stretch-elicited secretion triggers signals mediated by Gi/o protein, whereas agonists such as endothelin 1 independently signal through Gq. Discoordinated regulation is observed following stimulations by some cytokines, which selectively up-regulate BNP. This regulation takes place at the translational and transcriptional levels and is dependent on a p38 signaling pathway. Further details of processes regulating NP secretion need to be defined to develop a comprehensive view of the endocrine function of the heart. Nevertheless, translational research in the area of NPs has demonstrated the usefulness of these hormones as a marker of disease and as potential therapeutic agents. The latter application of NP is particularly attractive given that ANF and BNP possess pharmacologic actions that require polypharmacy in the treatment of acute myocardial infarction and congestive heart failure.

The endocrine function of the heart.

Atrial cardiocytes in the heart of mammals produce in a regulated manner the polypeptide hormones atrial natriuretic factor (ANF, ANP) and brain natriuretic peptide (BNP). The biological actions of ANF and BNP are similar; they include the modulation of systems that tend to increase extracellular fluid volume and blood pressure, such as the renin-angiotensin system and the sympathetic nervous system. Additionally, both hormones have potent growth-regulating properties. ANF and BNP signal by activating membrane-bound guanylyl cyclase receptors, leading to an increase in intracellular cGMP and thus affecting the activity of cGMP-regulated enzymes and ion channels. Under chronic hemodynamic overload, cardiac ANF and BNP synthesis and secretion are increased. This increase is viewed as a cardioprotective mechanism, given the beneficial effects of ANF and BNP on cardiac preload, afterload and cardiovascular growth. As discussed in this review, some basic facts regarding the synthesis and secretion of ANF and BNP and their peripheral effects remain to be clarified. Nevertheless, at the clinical level, the elevation of circulating ANF and BNP in heart failure or following acute coronary syndromes has been shown to have diagnostic and prognostic implications. Moreover, these peptides themselves hold promise as therapeutic agents in the treatment of heart failure. Additional pharmaceutical applications might be gleaned from current preclinical and clinical studies showing beneficial effects of ANF or BNP in the treatment of hypertension, bronchospasm and in tissue remodeling following acute myocardial infarction.

Neuroendocrine profiling of humans receiving cardiac allografts.

BACKGROUND: Several studies have investigated changes in circulating hormones and markers of cardiac status after heart transplantation in humans. As a result, plasma levels of various hormones and autocoids have been associated with cardiac allograft rejection status. However, no clear associations can be defined given the highly contradictory nature of the available literature. METHODS: In this study of 69 consecutive heart transplant patients followed for >2 years we examine the relationship between neurohumors potentially related to allograft rejection and endomyocardial biopsy grade of rejection (according to the ISHLT) and hemodynamic status. Markers assessed include brain natriuretic peptide (BNP), amino-terminal pro-BNP (N-BNP), atrial natriuretic factor (ANF), adrenomedullin, interleukin-1beta, interleukin-6, tumor necrosis factor-alpha, troponin C and C-reactive protein. RESULTS: The highest plasma levels for most neurohumors were found shortly after surgery and showed a trend towards normalization with time. BNP and N-BNP were the only significantly elevated plasma analytes for patients with Grade 3 rejection as compared with other ISHLT grades. ANF plasma levels correlated with BNP and N-BNP in Grades 0 to 2, but not in Grade 3, suggesting that in this rejection grade the usual coordinated changes observed in BNP and ANF secretion no longer exist. Cardiac filling pressures were correlated with plasma BNP, N-BNP and ANF levels only for Grades 0 and 1. CONCLUSIONS: The timing of blood sampling after transplantation influences the level of the neurohumors measured, which may help explain the conflicting literature reports on the association between neurohumor levels and rejection grade. The significant increase in circulating levels of BNP and N-BNP observed in most cases of Grade 3 rejection occurred with no apparent relationship to post-transplantation time, which suggests a specific influence of acute rejection on BNP gene expression.

Determinants of natriuretic peptide gene expression.

The cardiac natriuretic peptides (NP) atrial natriuretic factor or peptide (ANF or ANP) and brain natriuretic peptide (BNP) are polypeptide hormones synthesized, stored and secreted mainly by cardiac muscle cells (cardiocytes) of the atria of the heart. Both ANF and BNP are co-stored in storage granules referred to as specific atrial granules. The biological properties of NP include modulation of intrinsic renal mechanisms, the sympathetic nervous system, the rennin-angiotensin-aldosterone system (RAAS) and other determinants, of fluid volume, vascular tone and renal function. Studies on the control of baseline and stimulated ANF synthesis and secretion indicate at least two types of regulated secretory processes in atrial cardiocytes: one is stretch-stimulated and pertussis toxin (PTX) sensitive and the other is Gq-mediated and is PTX insensitive. Baseline ANF secretion is also PTX insensitive. In vivo, it is conceivable that the first process mediates stimulated ANF secretion brought about by changes in central venous return and subsequent atrial muscle stretch as observed in acute extracellular fluid volume expansion. The second type of stimulation is brought about by sustained hemodynamic and neuroendocrine stimuli such as those observed in congestive heart failure.

Determinants of inducible brain natriuretic peptide promoter activity.

Atrial natriuretic factor (ANF) and brain natriuretic peptide (BNP) are polypeptide hormones belonging to the cardiac-derived mammalian natriuretic peptide system. These hormones share the same biological properties and receptors and both play important roles in the maintenance of fluid and electrolyte balance and in cardiovascular growth. Most hemodynamic and neurohumoral stimuli can coordinately increase ANF and BNP gene expression. However, instances of discoordinated ANF and BNP gene expression have been described, providing an opportunity for investigating the mechanisms that differentially regulate the expression of the natriuretic peptide genes. For example, exposure of cardiocytes in culture to certain pro-inflammatory cytokines and conditioned medium from mixed lymphocyte cultures upregulate BNP but not ANF gene expression. BNP promoter activity is also upregulated under these conditions but the cis-acting elements involved in this phenomenon are not known. In comparison to the ANF gene, less is known about BNP promoter consensus elements that regulate gene expression by mechanical or neurohumoral agonists. A number of cis-acting elements for GATA, Nkx2.5, NF-kappaB and TEF transcription factors have recently been identified within the BNP promoter that regulate BNP expression in response to specific agonists. This review focuses on the information available regarding cis-acting determinants responsible for inducible BNP transcription.

Participation of G proteins in natriuretic peptide hormone secretion from heart atria.

The involvement of G proteins in the mechanism underlying the increased atrial natriuretic factor (ANF) secretion observed after atrial muscle stretch (stretch-secretion coupling) was assessed using a combined pharmacological, immunocytochemical, and tissue fractionation approach. It was found that G(i/o) inhibition by pertussis toxin (PTX) abolished stretch-secretion coupling without affecting baseline secretion through a mechanism that is independent of G(q) signaling agonists. Mastoparan-7, a G(i/o) agonist, significantly increased ANF secretion even in the absence of muscle stretch through a PTX-sensitive mechanism. By confocal and electron immunocytochemistry, ANF and G(o) partially colocalized, whereas ultracentrifugation analysis suggested the presence of two populations of granules, one of which was partially associated with G(o), as demonstrated by Western blotting. PTX did not affect basal or endothelin-1-stimulated ANF secretion, in line with the view that endothelin-1 signals mainly through G(q). It is concluded there are at least two types of regulated secretory processes in atrial cardiocytes: one is acutely responsive to muscle stretch and is PTX sensitive, and the other is G(q)mediated and PTX insensitive and may be responsible for changes in secretion after chronic changes in the neuroendocrine environment.

Selective upregulation of cardiac brain natriuretic peptide at the transcriptional and translational levels by pro-inflammatory cytokines and by conditioned medium derived from mixed lymphocyte reactions via p38 MAP kinase.

An increase in circulating brain natriuretic peptide (BNP) but not atrial natriuretic factor (ANF) is observed coincident with cardiac allograft rejection that is reversed upon treatment with anti-lymphocyte therapy suggesting that pro-inflammatory cytokines may uniquely modulate BNP gene expression and secretion. This study tested pro-inflammatory cytokines or conditioned medium (CM) derived from mixed- lymphocyte reaction (MLR) cultures in their ability to modulate ANF or BNP mRNA expression, secretion, as well as BNP promoter activity in cultured neonatal rat cardiocytes. IL-1 beta and TNF-alpha elicited a significant dose- and time-dependent increase in BNP mRNA, and secretion, whereas, ANF mRNA levels and secretion did not change. IL-1 beta and TNF-alpha rapidly increased phosphorylated p38 MAP kinase abundance and activity. Inhibition of p38 MAP kinase with SB203580 abolished IL-1 beta- and TNF-alpha-stimulated increase in BNP mRNA, promoter activity and secretion. MLR-CM in 20%, 50% and 100% proportions increased BNP but not ANF secretion. The MLR-induced increases in BNP secretion were completely abolished by SB203580 pre-treatment. These investigations show that exposure of cultured rat cardiocytes to specific pro-inflammatory cytokines as well as MLR-CM results in the only known instance of upregulation of cardiac BNP at the transcriptional and translational levels without a corresponding increase in ANF gene expression. Furthermore, these effects are dependent on signaling by p38 MAP kinase. In all, the findings reveal a unique dis-coordinated expression of BNP and ANF to inflammatory cytokines and offers an opportunity to better understand the differential regulation of these two cardiac-derived endocrine hormones that share receptors as well as biological properties.