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

[The heart as an endocrine organ]

The discovery of cardiac hormone production significantly changed the evaluation of the function of the heart, which is rather regarded as a determining factor of the electrolyte and hemodynamic homeostasis cooperating with other organ systems instead of a mechanical pump. The most important hormones produced by the heart are the natriuretic peptides that have the primary role of protection against volume overload through natriuretic, diuretic, vasodilator and antiproliferative effects. They are integrative markers of the cardiac, vascular and renal functions and marking cardiorenal distress. Brain natriuretic peptide and the N-terminal pro-hormone (NT-proBNP) became generally accepted markers of heart failure exceeding traditional pathophysiological significance of those. They are useful in the diagnosis, estimation of prognosis and therapy guidance and their therapeutic administration is also available. Although the detection of extraadrenal aldosterone production is an exciting new discovery, intracardial aldosterone production is not significant in human beings. The intracardial thyroid hormone production is regulated by deiodinase activity. The role of elevated T3 concentration was suggested in the development of cardiac hypertrophy, while low T3 is assumed to be important in adaptation to hypoxia. An unexpected, complex relation can be determined between epicardial adipose tissue and coronary artery diseases, cytokine and adipokine production of adipocytes might be a part of the self-enhancing process of atherosclerosis.

Relative Change in NT-proBNP Level: An Important Risk Predictor of Cardiovascular Congestion in Haemodialysis Patients

Background

Cross-sectional studies have shown that B-type natriuretic peptide (BNP) and its N-terminal fragment (NT-proBNP) are predictive of cardiovascular death in haemodialysis (HD) patients. In the present study, we tested the hypothesis that monitoring NT-proBNP measurements adds further prognostic information, i.e. predicts congestive heart failure (CHF) events.

Methods

In a prospective cohort of 236 HD patients, NT-proBNP levels were measured monthly during 18 months. Patients were divided according to the occurrence of CHF events. In a nested case-control study, we assessed the evolution of NT-proBNP levels.

Results

On average, the 236 HD patients were followed up for 12.5 months, a period during which 44 patients developed a CHF event (half requiring hospitalisation). At baseline, patients who developed a CHF event had significantly more dilated cardiomyopathy and/or altered left ventricular ejection fraction and higher NT-proBNP levels compared with patients who did not develop a CHF event. During follow-up, we observed a significant increase in NT-proBNP levels preceding the CHF event. At a 20% relative increase of NT-proBNP, the sensitivity of NT-proBNP as a predictor of CHF events was 0.57 and the specificity 0.77.

Conclusion

The relative change in NT-proBNP levels is a significant risk predictor of a CHF event.

Biomarkers in acute heart failure--state of the art

The role of biomarkers in the management of patients with acute heart failure (HF) has evolved rapidly in the past several years. Representing a major burden on health systems, acute HF has increased the need for earlier diagnosis, better risk stratification, and cost-effective treatment to reduce rates of hospitalization. Biomarker-guided diagnosis and treatment have become essential, especially in the acute setting to which the majority of the patients with acute HF initially present. Studies clearly demonstrate the complexity of these patients, who commonly have multiple comorbidities necessitating an integrative approach. Several groundbreaking studies conducted in the past decade have demonstrated how biomarkers, individually or in combination, can outperform conventional laboratory tests used in the emergency department as well as in hospitalized patients with acute HF. In this Review, we will provide an update on biomarkers considered state of the art in the diagnosis and management of patients with acute HF.

The role of plasma N-terminal pro-B-type natriuretic peptide in predicting the severity of transient tachypnea of the newborn

BACKGROUND/AIM

Transient tachypnea of the newborn (TTN) is a consequence of inadequate neonatal lung fluid clearance. Natriuretic peptides play an important role in the regulation of extracellular fluid volume. The aim of the study was to investigate the relation between plasma N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels and TTN, and to find out its role in predicting disease severity.

METHODS

A prospective controlled study involving 67 infants with TTN and 33 controls ≥34 weeks gestational age was conducted. Study and control groups were compared for plasma NT-proBNP levels measured on the 6th, 24th, 72nd and 120th hours of life. Cardiac systolic functions were evaluated by echocardiography.

RESULTS

NT-proBNP levels were significantly higher in neonates with TTN compared to controls at 6th, 24th, 72nd and 120th hours (p<0.001). NT-proBNP levels at 24th and 72nd hours were significantly higher in infants with prolonged tachypnea (p=0.007 and p=0.03) and in those who required respiratory support (p=0.006 and p<0.001). Tachypnea duration was correlated with NT-proBNP levels at 24h (r=0.41, p=0.001). At a cut-off value of 6575 pg/ml, NT-proBNP had a sensitivity of 85% and specificity of 64% to predict mechanical ventilation requirement. Cardiac systolic functions were normal in all TTN patients.

CONCLUSION

Plasma NT-proBNP levels are increased in neonates with TTN. Measurement of plasma NT-proBNP can be useful for predicting infants who will have prolonged tachypnea and mechanical ventilation requirement.

Prognostic utility of changes in N-terminal pro-brain natriuretic Peptide combined with sequential organ failure assessment scores in patients with acute lung injury/acute respiratory distress syndrome concomitant with septic shock

We investigated the prognostic utility of changes in N-terminal pro-brain natriuretic peptide (NT-proBNP) in combination with Sequential Organ Failure Assessment (SOFA) score in patients with acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) concomitant with septic shock. Forty-nine mechanically ventilated patients with ALI/ARDS concomitant with septic shock were studied. N-terminal pro-brain natriuretic peptide levels were measured on the first 3 days (days 0, 1, and 2) in the intensive care unit. The median NT-proBNP levels in survivors and nonsurvivors were 3,999 vs. 2,819 pg/mL on day 0 (P = 0.719); 4,495 vs. 5,397 pg/mL on day 1 (P = 0.543); and 2,325 vs. 14,173 pg/mL on day 2 (P = 0.028). N-terminal pro-brain natriuretic peptide levels increased significantly from baseline values in nonsurvivors only. We observed a monotonic increase in 28-day mortality associated with increasing quartiles of percent change in NT-proBNP on day 2 (P < 0.0001). Kaplan-Meier survival analysis revealed that mortality was significantly higher in patients with a change in NT-proBNP of 30% or more (log-rank P < 0.0001). On day 2, areas under the receiver operating characteristic curves for predicting 28-day mortality were 0.74 for SOFA alone and 0.85 (P = 0.028) for SOFA combined with percent change in NT-proBNP. In conclusion, in patients with ALI/ARDS concomitant with septic shock, a rising trend (high percent change) in NT-proBNP levels had better prognostic utility than absolute levels. The combination of percent change in NT-proBNP with SOFA may provide superior prognostic accuracy to SOFA alone.

Circulating forms of the b-type natriuretic peptide prohormone: pathophysiologic and clinical considerations

Recent studies reported that many different biochemical forms of B-type-related peptides circulate in human blood. In particular, a significant amount of the prohormone peptide (i.e., proBNP108) can be detected in plasma of patients with heart failure. These data indicate that the posttranslational maturation processing of the B-type natriuretic peptide (BNP) precursor may not be efficient in heart failure. The aim of this chapter is to describe the biochemical pathways of proBNP108 maturation and to discuss the pathophysiological relevance of alteration of the posttranslational maturation mechanisms in heart failure. An impaired cardiac endocrine function was proposed to explain the altered electrolyte and fluid homeostasis occurring in chronic heart failure. Recent studies demonstrated that a great part of BNPs assayed by immunoassay methods in healthy subjects and in patients with cardiovascular disease is devoid of biological activity. These findings suggest that an alteration in posttranslational maturation of BNP precursor may promote the resistance to biological action of BNP in patients with heart failure at a prereceptor level. These studies also open a new and more complex scenario regarding the circulating BNPs. The active hormone (i.e., BNP1-32) may be produced even in vivo from the circulating precursor proBNP108 by plasma enzyme degradation, such as the soluble form of corin, possibly able to process the circulating intact precursor of natriuretic hormones. As a future perspective, the simultaneous measurement of the proBNP1-108 and the active peptide BNP1-32 with more specific methods could allow a more accurate estimation of both production/secretion of B-type-related peptides from cardiomyocytes and the true activity of the cardiac endocrine function.

Comparison of Midregional Pro–A-Type Natriuretic Peptide and the N-Terminal Pro–B-Type Natriuretic Peptide for Predicting Mortality and Cardiovascular Events

BACKGROUND

N-terminal pro–B-type natriuretic peptide (NT-proBNP) provides prognostic information on mortality and future cardiovascular events for individuals from the general population. A novel immunoassay was recently developed that measures a midregional fragment of pro–A-type natriuretic peptide (MR-proANP). We compared the capabilities of MR-proANP and NT-proBNP for predicting mortality and cardiovascular events in a population-based study.

METHODS

A total of 7819 patients participated in the population-based Prevention of Renal and Vascular End-stage Disease (PREVEND) study, a prospective observational study. Three clinical end points were studied: all-cause mortality, cardiovascular mortality, and cardiovascular events. After a median follow-up of 10.5 years, we used a Cox proportional hazards model to investigate the relationship between the 2 natriuretic peptides and the clinical end points. The Harrell C statistic and the integrated discrimination improvement (IDI) were used to compare MR-proANP and NT-proBNP.

RESULTS

Increased plasma concentrations of both natriuretic peptides were associated with an increased risk of all-cause mortality and cardiovascular events, after adjustment for age, sex, and other cardiovascular risk factors. According to the Harrell C statistic analysis, the models with MR-proANP and NT-proBNP were comparable in predicting all-cause mortality, cardiovascular mortality, and cardiovascular events. In contrast to NT-proBNP, MR-proANP was not independently related to cardiovascular mortality. In all models, the IDI was higher for NT-proBNP than for MR-proANP.

CONCLUSIONS

MR-proANP was as efficient as NT-proBNP in predicting all-cause mortality, cardiovascular mortality, and cardiovascular events; however, its association with cardiovascular mortality was not independent from other confounders.

Influence of sex and hormone status on circulating natriuretic peptides

OBJECTIVES

The aim of this study was to assess the relationship between sex hormones and natriuretic peptide levels in community-based adults.

BACKGROUND

Women have higher circulating natriuretic peptide concentrations than men, but the mechanisms for these sex-related differences and the impact of hormone therapy are unclear. Experimental studies suggest that androgens may suppress natriuretic peptide secretion.

METHODS

We measured N-terminal pro-B-type natriuretic peptide (NT-proBNP), total testosterone, and sex hormone-binding globulin plasma levels in 4,056 men and women (mean age 40 ± 9 years) from the Framingham Heart Study Third-Generation cohort. Sex/hormone status was grouped as: 1) men; 2) post-menopausal women not receiving hormone replacement therapy; 3) pre-menopausal women not receiving hormonal contraceptives; 4) post-menopausal women receiving hormone replacement therapy; and 5) pre-menopausal women receiving hormonal contraceptives.

RESULTS

Circulating NT-proBNP levels were associated with sex/hormone status (overall p < 0.0001). Men had lower NT-proBNP levels than women of all menopause or hormone groups, and women receiving hormonal contraceptives had higher NT-proBNP levels than women who were not receiving hormone therapy (all p < 0.0001). These relationships remained significant after adjusting for age, body mass index, and cardiovascular risk factors. Across sex/hormone status groups, free testosterone (FT) levels decreased and sex hormone-binding globulin levels increased in tandem with increasing NT-proBNP levels. In sex-specific analyses, NT-proBNP levels decreased across increasing quartiles of FT in men (p for trend <0.01) and women (p for trend <0.0001). Adjustment for FT markedly attenuated the association between sex/hormone status and NT-proBNP concentrations.

CONCLUSIONS

These findings suggest that lower levels of circulating androgens and the potentiating effect of exogenous female hormone therapy contribute to the higher circulating NT-proBNP concentrations in women.

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.

Dietary salt exacerbates isoproterenol-induced cardiomyopathy in rats

Spontaneously hypertensive heart failure rats (SHHFs) take longer to develop compensated heart failure (HF) and congestive decompensation than common surgical models of HF. Isoproterenol (ISO) infusion can accelerate cardiomyopathy in young SHHFs, while dietary salt loading in hypertensive rats induces cardiac fibrosis, hypertrophy, and--in a minority-congestive HF. By combining ISO with dietary salt loading in young SHHFs, the authors sought a nonsurgical model that is more time--and resource-efficient than any of these factors alone. The authors hypothesized that salt loading would enhance ISO-accelerated cardiomyopathy, promoting fibrosis, hypertrophy, and biochemical characteristics of HF. SHHFs (lean male, 90d) were infused for 4 wk with ISO (2.5 mg/kg/day) or saline. After 2 wk of infusion, a 6-wk high-salt diet (4%, 6%, or 8% NaCl) was initiated. Eight percent salt increased heart weight, HF markers (plasma B-type natriuretic peptide, IL-6), lung lymphocytes, and indicators of lung injury and edema (albumin and protein) relative to control diet, while increasing urine pro-atrial natriuretic peptide relative to ISO-only. High salt also exacerbated ISO-cardiomyopathy and fibrosis. Thus, combining ISO infusion with dietary salt loading in SHHFs holds promise for a new rat HF model that may help researchers to elucidate HF mechanisms and unearth effective treatments.

B-type natriuretic peptide secretion following scuba diving

AIM

To examine the neurohormonal effects of a scuba dive, focusing on the acute changes in the plasma concentrations of the different peptide fragments from the B-type natriuretic peptide (BNP) precursor.

MATERIALS & METHODS

We studied 12 healthy scuba divers (mean age ± standard deviation: 44 ± 7 years; range: 34-55 years; BMI: 24.8 ± 2.8 kg/m(2)), who performed a 15-m depth dive in salt water, with a bottom time of 30 min. Blood samples for BNPs (pro-B-type natriuretic peptide [pro-BNP], BNP and aminoterminal pro-BNP) and catecholamines were measured in plasma before immersion, and after the dive. A continuous electrocardiographic recording was obtained during the entire protocol.

RESULTS

BNP, aminoterminal pro-BNP and pro-BNP plasma concentrations slightly, but significantly, increased after the scuba dive (18 ± 15 to 21 ± 11 ng/l, p = 0.020; 32 ± 19 to 38 ± 21 ng/l, p = 0.008; and 7.8 ± 1.6 to 10.3 ± 3.6 ng/l, p = 0.028, respectively) in parallel with norepinephrine concentration (743 ± 323 to 1163 ± 656 ng/l, p = 0.014), with no variations in total plasma proteins, hematocrit or osmolality. A persistent sinus tachycardia was observed during all phases of the dive.

CONCLUSIONS

A 15-m depth scuba dive induces an acute slight release of the different peptide fragments from the BNP precursor, likely through the stimulation of a constitutive secretory pathway promoted by adrenergic activation and cardiac chamber dilation.

Thirty years of the heart as an endocrine organ: physiological role and clinical utility of cardiac natriuretic hormones

Thirty years ago, De Bold et al. ( 20 ) reported that atrial extracts contain some biologically active peptides, which promote a rapid and massive diuresis and natriuresis when injected in rats. It is now clear that the heart also exerts an endocrine function and in this way plays a key role in the regulation of cardiovascular and renal systems. The aim of this review is to discuss some recent insights and still-debated findings regarding the cardiac natriuretic hormones (CNHs) produced and secreted by cardiomyocytes (i.e., atrial natriuretic peptide and B-type natriuretic peptide). The functional status of the CNH system depends not only on the production/secretion of CNHs by cardiomyocytes but also on both the peripheral activation of circulating inactive precursor of natriuretic hormones and the transduction of the hormone signal by specific receptors. In this review, we will discuss the data supporting the hypothesis that the production and secretion of CNHs is the result of a complex integration among mechanical, chemical, hemodynamic, humoral, ischemic, and inflammatory inputs. The cross talk among endocrine function, adipose tissue, and sex steroid hormones will be discussed more in detail, considering the clinically relevant relationships linking together cardiovascular risk, sex, and body fat development and distribution. Finally, we will review the pathophysiological role and the clinical relevance of both peripheral maturation of the precursor of B-type natriuretic peptides and hormone signal transduction .

Systems biology and heart failure: concepts, methods, and potential research applications

Dramatic advances in molecular biology dominated twentieth century biomedical science and delineated the function of individual genes and molecules in exquisite detail. However, biological processes cannot be fully understood based on the properties of individual genes and molecules alone, since these elements act in concert to enable the specific functions that make for living cells and organisms. The discipline of systems biology provides a novel conceptual framework for understanding biological phenomenon. Systems biology synthesizes information concerning the interactions of genes and molecules and allows characterization of the supramolecular networks and functional modules that represent the most essential aspects of cell organization and physiology.

Relationships between serum levels of thyroid hormones and serum concentrations of asymmetric dimethylarginine (ADMA) and N-terminal-pro-B-type natriuretic peptide (NT-proBNP) in patients with Graves' disease

Endothelial dysfunction as well as abnormal thyroid hormone levels may be responsible for increased cardiovascular risk in Graves' disease (GD). Asymmetric dimethylarginine (ADMA) and N-terminal-pro-B-type natriuretic peptide (NT-proBNP) are new markers of endothelial and myocardial dysfunction, respectively. The purpose of this study was to investigate the relationship among the serum levels of ADMA, NT-proBNP, and thyroid hormones in GD patients. This was a cross-sectional investigation conducted in a university teaching hospital. Two hundred and thirty-nine GD (Female: 182, Male: 57) patients and 81 normal controls were enrolled in this study. Serum levels of ADMA were positively related with FT3 (r = 0.584, P < 0.001), FT4 (r = 0.551, P < 0.001), and TRAb levels (r = 0.502, P < 0.001). Serum NT-proBNP levels were positively associated with FT3 (r = 0.243, P < 0.001) and FT4 levels (r = 0.274, P < 0.001), as well as heart rate (r = 0.271, P < 0.03). The elevation of serum ADMA and NT-proBNP levels were also observed in patients with controlled hyperthyroidism. It is thus concluded that serum ADMA and NT-proBNP levels were increased in GD patients. Future studies may determine the usefulness of these two biomarkers to detect early signs of endothelial dysfunction, vascular stiffness, and fluid volume in GD patients.

Diagnostic, prognostic and therapeutic relevance of B-type natriuretic hormone and related peptides in children with congenital heart diseases

The aim of this article is to review the diagnostic and prognostic relevance of measurement of brain natriuretic peptide (BNP) and N-terminal pro-brain natriuretic peptide (NT-proBNP) in pediatric patients with congenital cardiac diseases (CHD). A computerized literature search in the National Library of Medicine using the keywords "BNP assay" and "NT-proBNP assay"+neonate/s and newborn/s was performed. Next, we refined the analysis to include only the studies specifically designed to evaluate the clinical usefulness of BNP and NT-proBNP measurements in children with CHD. Several authors suggested that BNP/NT-proBNP is clinically helpful as a diagnostic and prognostic marker for children with suspected CHD. BNP values are age dependent, even in paediatric populations. Unfortunately, accurate reference values for BNP and NT-proBNP for neonatal ages have only recently become available. As a result, the lack of homogenous and accurate decisional levels in the neonatal period greatly limits the clinical impact of the BNP assay, and also contributed to the production of conflicting results. Regardless of age, there is great variability in BNP/NT-proBNP values among CHD characterized by different hemodynamic and clinical conditions. In particular, cardiac defects characterized by left ventricular volume and pressure overload usually show a higher BNP response than CHD which is characterized by right ventricular volume or pressure overload. BNP and NT-proBNP may be considered helpful markers in the integral clinical approach for patients with CHD. Measurement of BNP cannot replace cardiac imaging (including echocardiography, angiography and magnetic resonance), but provide independent, low cost and complementary information for the evaluation of cardiac function and clinical status.

Usefulness of mid regional pro-atrial natriuretic peptide in the exacerbations of chronic obstructive pulmonary disease

BACKGROUND

A recent approach for the management of chronic obstructive pulmonary disease (COPD) is the measurement of systemic biomarkers. The aim of this study was to evaluate the usefulness of mid regional pro-atrial natriuretic peptide (MR-proANP) to predict short and long term prognosis.

METHODS

We included 318 COPD patients: 46 in a stable phase, 217 undergoing an exacerbation and 55 with pneumonia. Serum samples were collected at admission. For 20 exacerbated patients, we also collected a second sample one month later. MR-proANP was measured by an inmunofluorescent assay.

RESULTS

Statistically higher levels of MR-proANP were found in patients with pneumonia when comparing to patients in the stable state (p=0.031). For those patients with paired samples, MR-proANP decreased statistically one month later (p=0.027). MR-proANP showed significant lower levels in exacerbations with isolation of pathogenic bacteria (p=0.011). MR-proANP levels were higher in patients that died within one month, decreasing as long as the moment of death occurred later on (p=0.163).

CONCLUSIONS

The identification of exacerbation etiology by means of MR-proANP is not clinically reliable. Levels of MR-proANP vary depending on the clinical status, being higher during pneumonia in comparison to the stable state. MR-proANP levels were higher in patients that died within one month after the exacerbation episode.

Catecholamines, cardiac natriuretic peptides and chromogranin A: evolution and physiopathology of a 'whip-brake' system of the endocrine heart

In the past 50 years, extensive evidence has shown the ability of vertebrate cardiac non-neuronal cells to synthesize and release catecholamines (CA). This formed the mindset behind the search for the intrinsic endocrine heart properties, culminating in 1981 with the discovery of the natriuretic peptides (NP). CA and NP, co-existing in the endocrine secretion granules and acting as major cardiovascular regulators in health and disease, have become of great biomedical relevance for their potent diagnostic and therapeutic use. The concept of the endocrine heart was later enriched by the identification of a growing number of cardiac hormonal substances involved in organ modulation under normal and stress-induced conditions. Recently, chromogranin A (CgA), a major constituent of the secretory granules, and its derived cardio-suppressive and antiadrenergic peptides, vasostatin-1 and catestatin, were shown as new players in this framework, functioning as cardiac counter-regulators in 'zero steady-state error' homeostasis, particularly under intense excitatory stimuli, e.g. CA-induced myocardial stress. Here, we present evidence for the hypothesis that is gaining support, particularly among human cardiologists. The actions of CA, NP and CgA, we argue, may be viewed as a hallmark of the cardiac capacity to organize 'whip-brake' connection-integration processes in spatio-temporal networks. The involvement of the nitric oxide synthase (NOS)/nitric oxide (NO) system in this configuration is discussed. The use of fish and amphibian paradigms will illustrate the ways that incipient endocrine-humoral agents have evolved as components of cardiac molecular loops and important intermediates during evolutionary transitions, or in a distinct phylogenetic lineage, or under stress challenges. This may help to grasp the old evolutionary roots of these intracardiac endocrine/paracrine networks and how they have evolved from relatively less complicated designs. The latter can also be used as an intellectual tool to disentangle the experimental complexity of the mammalian and human endocrine hearts, suggesting future investigational avenues.

N-terminal pro-brain natriuretic peptide as a marker of right ventricular dysfunction after open-lung approach in patients with acute lung injury/acute respiratory distress syndrome

PURPOSE

The purpose of the study was to evaluate the utility of N-terminal pro-brain natriuretic peptide (NT-proBNP) as a marker of right ventricular (RV) dysfunction after open-lung approach (OLA) in patients with acute lung injury (ALI)/acute respiratory distress syndrome (ARDS).

MATERIALS AND METHODS

Twenty-seven patients with ALI/ARDS underwent OLA (2-minute steps of fixed pressure-controlled ventilation with progressive positive end-expiratory pressure levels up to 30 cm H(2)O, followed by stepwise decrement of positive end-expiratory pressure level by 2 cm H(2)O). Patients who showed a PaO(2)/FiO(2) increase of more than 50% from baseline were defined as responders. Plasma NT-proBNP levels were taken immediately before OLA and 2 and 6 hours later. A minimum 30% increase in NT-proBNP level from baseline was considered significant.

RESULTS

Right-over-left ventricular stroke work ratio and its percentage change did not differ between responders and nonresponders, whereas these values were higher in patients showing NT-proBNP increase (P < .05). The NT-proBNP percentage change correlated with right-over-left ventricular stroke work ratio percentage change (r = 0.83), pulmonary vascular resistance (r = 0.81), and RV ejection fraction (r = -0.79) and correlated with plateau pressure in nonresponders only (r = 0.82).

CONCLUSIONS

In patients with ALI/ARDS, intraindividual NT-proBNP changes correlated with RV afterload following OLA, thereby serving as a potential marker for RV dysfunction after OLA.

Blood N-terminal proBNP as a potential indicator of cardiac preload in patients with high volume load

Stroke volume is mainly determined by preload, afterload and contractility. Accordingly, measuring cardiac preload provides essential information for treatment of hemodynamically unstable patients. Hemodynamic monitoring is widely used to measure cardiac preload, but the monitoring method is time-consuming and invasive. It is therefore important to establish a simple and non-invasive test for monitoring cardiac preload. Brain natriuretic peptide (BNP), which lowers systemic vascular resistance, is synthesized as proBNP in response to myocardial wall stretch, and blood BNP has been used as an indicator of preload. Here, we measured blood level of N-terminal proBNP (NT-proBNP), which is generated during processing of proBNP, because NT-proBNP is stable and easily measured at the bedside. To assess the correlation between blood NT-proBNP and preload, we also measured the global end-diastolic volume index (GEDVI) that reflects the cardiac preload. GEDVI was calculated with the volumes in all chambers of the heart at the time of end-diastole. Eight male patients (57.6 +/- 25.3 years old) with high volume load (1,000 ml within 4 hours) were included in the present study: 3 subjects with burn, 3 subjects with sepsis, a patient with alcoholic ketoacidosis and a resuscitated patient. Blood levels of NT-proBNP were 1,316.3 +/- 1,154.5 pg/ml (47 blood samples from the eight patients; the normal range, < 125 pg/ml). Notably, the increase in the NT-proBNP levels was associated with the increased GEDVI (r = 0.61, p < 0.0001). Therefore, blood NT-proBNP may be a good indicator of cardiac preload in patients with high volume load.

Hemodynamic determinants of myocardial B-type natriuretic peptide release: relative contributions of systolic and diastolic wall stress

Although B-type natriuretic peptide (BNP) is widely used as a biomarker for heart failure, the in vivo mechanical stimulus for its cardiac release remains poorly defined. We aimed to characterize the hemodynamic determinants of the transcardiac BNP gradient as a measure of myocardial BNP release by performing a detailed hemodynamic assessment in subjects with a broad spectrum of systolic and diastolic left ventricular dysfunction. Forty-two subjects underwent a detailed transthoracic echocardiographic study, right heart catheterization, and simultaneous BNP measurement in arterial and coronary sinus plasma. The transcardiac BNP gradient was lowest in subjects with normal left ventricular ejection fraction/high peak early diastolic annular velocity (n=11), intermediate in those with normal left ventricular ejection fraction/low peak early diastolic annular velocity (n=13), and highest in those with low left ventricular ejection fraction/low peak early diastolic annular velocity (n=18; 29 ng/L (range: 15 to 78 ng/L) versus 88 ng/L (range: 34 to 172 ng/L) versus 1566 ng/L (range: 624 to 2349 ng/L; P<0.001). Across the range of patients, left ventricular end-systolic wall stress (r(2)=0.51) and peak systolic mitral annular velocity (r(2)=0.47) showed the strongest correlation with higher transcardiac BNP gradient. In contrast, the transcardiac BNP gradient was weakly related to indices of diastolic load, including pulmonary capillary wedge pressure (r(2)=0.27) and left ventricular end-diastolic wall stress (r(2)=0.21). Across this spectrum of pathophysiology, left ventricular end-systolic wall stress appears to be the key mechanical stimulus influencing cardiac BNP release.

Mouse phenotyping

Model organisms like the mouse are important tools to learn more about gene function in man. Within the last 20 years many mutant mouse lines have been generated by different methods such as ENU mutagenesis, constitutive and conditional knock-out approaches, knock-down, introduction of human genes, and knock-in techniques, thus creating models which mimic human conditions. Due to pleiotropic effects, one gene may have different functions in different organ systems or time points during development. Therefore mutant mouse lines have to be phenotyped comprehensively in a highly standardized manner to enable the detection of phenotypes which might otherwise remain hidden. The German Mouse Clinic (GMC) has been established at the Helmholtz Zentrum München as a phenotyping platform with open access to the scientific community (www.mousclinic.de; [1]). The GMC is a member of the EUMODIC consortium which created the European standard workflow EMPReSSslim for the systemic phenotyping of mouse models (http://www.eumodic.org/[2]).

Reference intervals for brain natriuretic peptide in healthy newborns and infants measured with an automated immunoassay platform

BACKGROUND

In order to assess the reference intervals for B-type natriuretic hormone (BNP) in the first days of life, we measured peptide concentrations using the fully automated Access platform.

METHODS

Plasma BNP was measured in 188 apparently healthy newborns and infants throughout the first month of extra-uterine life, as well as in 245 healthy infants ranging from 1 month to 12 years of age.

RESULTS

BNP showed the highest concentrations in the first 2 days of life, with a progressive decline afterwards. Moreover, BNP values in the first week of life were significantly higher (p<0.0001) than values observed in the next periods. As a result, a significant negative correlation was found between BNP and age values when considering all 433 samples (rho=-0.816, p<0.0001 by the Spearman rank correlation test). There was no significant difference between BNP values found in males and females.

CONCLUSIONS

According to this data, our study indicates that at least two reference intervals should be used for newborns and infants. The first, with higher BNP values for neonates in the first week of extra-uterine life, and the other, with lower BNP values for infants aged 2 weeks to 12 years.

Upregulation of ANP and NPR-C mRNA in the kidney and heart of eNOS knockout mice

OBJECTIVES

The aim of the present studywas to examine the question of whether the atrial natriuretic peptide (ANP) system is altered by endothelial nitric-oxide synthase (eNOS).

METHODS

Male eNOS-deficient mice (eNOS-/-) and wild type control mice (eNOS+/+, C57B1/6J) were used. Blood pressure was measured in anesthetized mice by tail cuff plethysmography and renal function was measured. Expression of ANP, natriuretic peptide receptor (NPR)-A, NPR-C, and tonicity-responsive enhancer binding protein (TonEBP) mRNA was determined by real-time PCR. Localization of (125)I-ANP binding sites was measured using in vitro autoradiography.

RESULTS

In eNOS-/- mice, systolic blood pressure increased and left ventricular hypertrophy was observed. Urine volume and osmolarity did not change. Expression of ANP markedly increased in the heart and kidney of eNOS-/- mice. Expression of NPR-A and NPR-C increased in the heart and tended to increase in the kidney of eNOS-/- mice. In the renal medulla in particular, increased expression of NPR-C was more prominent. Expression of TonEBP mRNA was markedly decreased in the renal medulla, but not in the renal cortex. Maximum binding capacity (B(max)) of ANP and C-ANP increased in the renal medulla in eNOS-/- mice.

CONCLUSION

These results suggest that the eNOS-NO system may be partly involved in regulation of ANP, NPR-A, -C, and TonEBP mRNA expression in the kidney.

Fas (CD95) induces rapid, TLR4/IRAK4-dependent release of pro-inflammatory HMGB1 from macrophages

Although Fas (CD95) is recognized as a death receptor that induces apoptosis, recent studies indicate that the Fas/FasL system can induce pro-inflammatory cytokine production by macrophages independent of conventional caspase-mediated apoptotic signaling. The precise mechanism(s) by which Fas activates macrophage inflammation is unknown. We hypothesized that Fas stimulates rapid release of high mobility group box 1 (HMGB1) that acts in an autocrine and/or paracrine manner to stimulate pro-inflammatory cytokine production via a Toll-like receptor-4 (TLR4)/Interleukin-1 receptor associated kinase-4 (IRAK4)-dependent mechanism. Following Fas activation, HMGB1 was released within 1 hr from viable RAW267.4 cells and primary murine peritoneal macrophages. HMGB1 release was more rapid following Fas activation compared to LPS stimulation. Neutralization of HMGB1 with an inhibitory anti-HMGB1 monoclonal antibody strongly inhibited Fas-induced production of tumor necrosis factor (TNF) and macrophage inflammatory protein-2 (MIP-2). Both Fas-induced HMGB1 release and associated pro-inflammatory cytokine production were significantly decreased from Tlr4^-/- and Irak4^-/- macrophages, but not Tlr2^-/- macrophages. These findings reveal a novel mechanism underlying Fas-mediated pro-inflammatory physiological responses in macrophages. We conclude that Fas activation induces rapid, TLR4/IRAK4-dependent release of HMGB1 that contributes to Fas-mediated pro-inflammatory cytokine production by viable macrophages.

The interplay between chromogranin A-derived peptides and cardiac natriuretic peptides in cardioprotection against catecholamine-evoked stress

Chromogranin A (CgA) is the major soluble protein co-stored and co-released with catecholamines (CAs) from secretory vesicles in the adrenal medulla chromaffin cells. Present in the diffuse neuroendocrine system, it has also been detected in rat and human cardiac secretory granules where it co-stores with natriuretic peptide hormones (NPs). Mounting evidence shows that CgA is a marker of cardiovascular dysfunctions (essential hypertension, hypertrophic and dilatative cardiomyopathy, heart failure) and precursor of the cardioactive peptides vasostatin-1 (VS-1) and catestatin (Cts). This review focuses on recent knowledge regarding the myocardial, coronary and anti-adrenergic actions of VS-1. In particular, the negative inotropism, lusitropism and coronary dilation effects of rat CgA1-64 (rCgA) and human recombinant STACgA1-78 (hrSTACgA1-78) are summarized with attention on their counteracting isoproterenol- and endothelin-1-induced positive inotropism, as well as ET-1-dependent coronary constriction. The interactions between vasostatins (VSs), NPs and CA receptors are proposed as a paradigm of the heart capacity to organize complex connection-integration processes for maintaining homeostasis under intense cardio-excitatory stimuli (myocardial stress).

Amino-terminal fragment of the prohormone brain-type natriuretic peptide in rheumatoid arthritis

OBJECTIVE

Increased concentrations of N-terminal pro-brain natriuretic peptide (NT-proBNP) are associated with cardiovascular morbidity and mortality, but little is known about their relationship to chronic inflammation. Patients with rheumatoid arthritis (RA) have chronic inflammation, increased arterial stiffness, and accelerated coronary atherosclerosis. This study was undertaken to test the hypothesis that NT-proBNP concentrations are elevated in patients with RA and are associated with coronary artery calcification and markers of inflammation.

METHODS

In 159 patients with RA (90 with early RA and 69 with longstanding RA) without heart failure and 88 control subjects, serum concentrations of NT-proBNP, interleukin-6 (IL-6), and tumor necrosis factor alpha (TNFalpha) were measured and coronary calcification was assessed. Associations between NT-proBNP levels and the other parameters were investigated.

RESULTS

NT-proBNP concentrations were elevated in patients with longstanding RA (median 142.8 pg/ml [interquartile range 54.8-270.5]) and those with early RA (median 58.1 pg/ml [interquartile range 19.4-157.6]) compared with controls (18.1 [3.2-46.0]) (P < 0.001). In patients with RA, NT-proBNP concentrations were associated with age (rho = 0.35, P < 0.001), levels of IL-6 (rho = 0.33, P < 0.001), TNFalpha (rho = 0.23, P = 0.003), and C-reactive protein (CRP) (rho = 0.21, P = 0.01), coronary calcium score (rho = 0.30, P < 0.001), systolic blood pressure (rho = 0.30, P < 0.001), and disease activity (rho = 0.29, P < 0.001). After adjustment for age, race, and sex, the associations between NT-proBNP concentrations and disease activity, TNFalpha, IL-6, and CRP remained significant, but those with systolic blood pressure and coronary calcium score were attenuated.

CONCLUSION

NT-proBNP concentrations are increased in patients with RA without clinical heart failure and may indicate subclinical cardiovascular disease and a chronic inflammatory state.

Impact of increased body mass index on accuracy of B-type natriuretic peptide (BNP) and N-terminal proBNP for diagnosis of decompensated heart failure and prediction of all-cause mortality

BACKGROUND

BNP and N-terminal proBNP (NT-proBNP) concentrations may be depressed in patients with increased body mass index (BMI). Whether increased BMI affects accuracy of these biomarkers for diagnosing decompensated heart failure (HF) and predicting outcomes is unknown.

METHODS

We measured BNP and NT-proBNP in 685 patients with possible decompensated HF in a free-living community population subdivided by BMI as obese, overweight, and normal weight. HF diagnosis was adjudicated by a cardiologist blinded to BNP and NT-proBNP results. We tabulated all-cause mortality over a median follow-up of 401 days and assessed marker accuracy for HF diagnosis and mortality by ROC analysis.

RESULTS

Of the 685 patients, 40.9% were obese (n = 280), 28.2% were overweight (n = 193), and 30.9% had normal BMI (n = 212). Obese patients had lower BNP and NT-proBNP compared with overweight or normal-weight individuals (P < 0.001) and decreased mortality compared with normal-weight individuals (P < 0.001). Both biomarkers added significantly to a multivariate logistic regression model for diagnosis of decompensated HF across BMI categories. NT-proBNP outperformed BNP for predicting all-cause mortality in normal-weight individuals (chi(2) for BNP = 6.4, P = 0.09; chi(2) for NT-proBNP = 16.5, P < 0.001). Multivariate regression showed that both biomarkers remained significant predictors of decompensated HF diagnosis in each BMI subgroup.

CONCLUSIONS

In this study population, obese patients had significantly lower BNP and NT-proBNP that reflected lower mortality. BNP and NT-proBNP can be used in all BMI groups for decompensated HF diagnosis, although BMI-specific cutpoints may be necessary to optimize sensitivity.

The response of circulating brain natriuretic peptide to academic stress in college students

Brain natriuretic peptide (BNP), a cardiac peptide, has been implicated in the regulation of hypothalamic-pituitary-adrenocortical (HPA) responses to psychological stressors. The influence of academic stress on circulating concentration of the N-terminal fragment of BNP precursor (NT-proBNP), and in relation to the stress hormone (cortisol) response was studied in 170 college students undergoing major examinations. Just prior to the examination, we measured self-estimated stress level, systolic, and diastolic blood pressure (SBP, DBP), heart rate (HR), plasma levels of cortisol, and NT-proBNP. These parameters were compared to the participants' baseline measurements, taken at the same hour of a different 'control day', without a major examination to induce stress. Hemodynamic variables (SBP, DBP, and HR) increased on the examination day compared with baseline values ( p < 0.001). Circulating cortisol concentration increased before examinations (+42%, p < 0.001). The response to stress was marked by a significant decrease in plasma NT-proBNP concentration (-40%, p < 0.001). We found in males a significant interaction between the cortisol elevation with examination stress and the NT-proBNP reduction ( p = 0.02). In response to academic stress, the plasma cortisol elevation was accompanied by a marked reduction in plasma NT-proBNP level. These data may indicate that mental stress entails an interface between the HPA axis and the peripheral natriuretic peptide system, leading to reciprocating changes in circulating levels of the corresponding hormones.

Asymmetrical myocardial expression of natriuretic peptides in pacing-induced heart failure

High-frequency pacing of the left ventricle (LV) free wall causes a dyssynchronous pattern of contraction that leads to progressive heart failure (HF) with pronounced differences in regional contractility. Aim of this study was to evaluate possible changes in brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) mRNA expression in the anterior/anterior lateral region (pacing site, PS) as compared to the infero-septal region (opposite site, OS) and to explore possible association between the contractiling pattern and biomarker expression. Cardiac tissue was collected from minipigs with pacing-induced HF (n=8) and without (control, n=6). The samples were selectively harvested from the anterior left ventricular (LV) wall, PS, and from an area remote to the pacing-site, OS. BNP and CNP mRNA expression was evaluated by semi-quantitative polymerase chain reaction (PCR). A significant difference in BNP expression was found in the PS between HF animals and controls (BNP/GAPDH: 0.65+/-0.11 vs. 0.35+/-0.04, p=0.02), but not in the OS (BNP/GAPDH: 0.36+/-0.05, ns vs. controls). CNP expression was not different compared to controls, although higher levels were observed in the PS and in the OS with respect to the controls (CNP/GAPDH: controls 0.089+/-0.036, PS 0.289+/-0.23, OS 0.54+/-0.16). This finding was in tune with an increase of CNP tissue concentration (controls: 0.69+/-0.13; PS=1.56+/-0.19; OS=1.70+/-0.42 pg/mg protein; p=0.039 controls vs. OS). Higher BNP mRNA expression in the PS is consistent with a reduction in contractile function in this region, while higher CNP mRNA expression in the OS suggests the presence of concomitant endothelial dysfunction in the remote region.

Hypoxia induces B-type natriuretic peptide release in cell lines derived from human cardiomyocytes

B-type natriuretic peptide (BNP) is a peptide hormone of myocardial origin with significant cardioprotective properties. Patients with myocardial ischemia present with high levels of BNP in plasma and elevated expression in the myocardium. However, the molecular mechanisms of BNP induction in the ischemic myocardium are not well understood. The aim of the investigation was to assess whether myocardial hypoxia induces the production of BNP in human ventricular myocytes. To test the hypothesis that reduced oxygen tension can directly stimulate BNP gene expression and release in the absence of hemodynamic or neurohormonal stimuli, we used an in vitro model system of cultured human ventricular myocytes (AC16 cells). Cells were cultured under normoxic (21% O2) or hypoxic (5% O2) conditions for up to 48 h. The accumulation of BNP, atrial natriuretic peptide (ANP), and vascular endothelial growth factor (VEGF) was then measured. Hypoxia stimulated the protein release of BNP and VEGF but not ANP. In concordance, the increased mRNA levels of BNP and VEGF but not ANP were found on culturing AC16 cells under hypoxic conditions. The analysis of the transcriptional activity of the hypoxia-inducible factor 1 (HIF-1) in nuclear extracts showed that HIF-1 activity was induced under hypoxic conditions. Finally, the treatment of AC16 cells with the HIF-1 inhibitor rotenone in hypoxia inhibited BNP and VEGF release. In conclusion, these data indicate that hypoxia induces the synthesis and secretion of BNP in human ventricular myocytes, likely through HIF-1-enhanced transcriptional activity.

Variability of N-Terminal Probrain Natriuretic Peptide in Stable Chronic Heart Failure and Its Relation to Changes in Clinical Variables

Background: We investigated the variability of N-terminal probrain natriuretic peptide (NT-proBNP) and its relation to known confounding variables in patients with stable chronic heart failure who were on a stable optimized medication regimen.

Methods: At 4 sampling intervals (14-day, 1-month, 2-month, and 3-month) the results for NT-proBNP measurements and several clinical variables were measured in samples from 41 patients with chronic systolic dysfunction who met 21 prespecified criteria for stability.

Results: Mean within-person NT-proBNP variabilities expressed as percentage CV were 17.6%, 18.9%, 15.5%, and 16.2% at 14-day, 1-month, 2-month, and 3-month follow-up, respectively, and the corresponding reference change values were 34.6%, 52.5%, 43.1%, and 45.0%, respectively. Within-person variability of NT-proBNP was not found to be associated with renal function, weight, or waist circumference. Likewise, age, sex, baseline NT-proBNP, New York Heart Association functional class, and ejection fraction did not influence variability of NT-proBNP. The index of individuality ranged from 0.07–0.15 depending on the time interval between test results.

Conclusions: Although other reported studies have revealed variations in the range of 80%, in this prespecified stable heart-failure population variation of NT-proBNP at 14-day, 1-month, 2-month, and 3-month follow-up was lower and was not related to renal function or weight. In view of the low index of individuality we observed, within-person variation is quite low compared to between-person variation. Consideration of these facts is important for the interpretation of clinical trials and the use of NT-proBNP in monitoring patients with heart failure.

Genetic Polymorphisms of the Natriuretic Peptide System in the Pathogenesis of Cardiovascular Disease: What Lies on the Horizon?

Background: The natriuretic peptide hormone family includes various proteins characterized by similar chemical structure and shared biological functions, with important effects on the cardiovascular system. Accordingly, these molecules are widely recognized as key clinical biomarkers in the diagnosis and monitoring of heart failure, hypertension, and coronary heart disease.

Content: Several single-nucleotide polymorphisms have been recently identified in genes associated with the natriuretic system. This review provides an overview of new insights into the functional role of these genetic variants, as well as their impact on cardiovascular physiopathology and drug response.

Conclusions: Noteworthy relationships between some specific polymorphisms and clinical correlates of cardiovascular disease have emerged. Nevertheless, future confirming studies are needed to substantiate the clinical relevance of such variants.

Abnormal NT-pro-BNP levels in asymptomatic long-term survivors of childhood cancer treated with anthracyclines

BACKGROUND

Anthracycline-induced cardiotoxicity can cause serious health problems for an increasing number of survivors of childhood malignancies. The aims of this study were to document plasma concentrations of cardiac troponin T (cTnT) and NT-pro-brain natriuretic peptide (NT-pro-BNP) in a large group of asymptomatic long-term survivors of childhood cancer treated with anthracyclines, and to study the relation of the abnormal biomarker levels with different risk factors for anthracycline-induced cardiotoxicity and conventional echocardiographic parameters.

PROCEDURES

One hundred twenty-two asymptomatic survivors of childhood cancer underwent a detailed echocardiography. Blood samples were taken to determine the levels of NT-pro-BNP and cTnT.

RESULTS

None of the survivors had abnormal cTnT levels. Thirteen percent of the survivors (n = 16) had abnormal NT-pro-BNP levels. Abnormal NT-pro-BNP levels were significantly related to cumulative anthracycline dosage (P < 0.003). Eleven of 31 survivors (35%) treated with cumulative anthracycline dose of 300 mg/m(2) or more, had abnormal NT-pro-BNP levels which were significantly related to end-diastolic left ventricular internal diameter (LVIDd) indexed for body surface area (BSA) (P < 0.01).

CONCLUSION

Cardiac TnT does not contribute to the early detection of late onset anthracycline-induced cardiotoxicity. Abnormal levels of NT-pro-BNP were detected in 13% of 122 asymptomatic, long-term survivors of childhood cancer. Follow-up of these survivors is essential to answer the question whether NT-pro-BNP is an early marker for late onset anthracycline-induced cardiotoxicity.