Excessive cerebral accumulation of the 42-residue amyloid beta-protein (Abeta) is an early and invariant step in the pathogenesis of Alzheimer's disease. Many studies have examined the cellular production of Abeta from its membrane-bound precursor, including the role of the presenilin proteins therein, but almost nothing is known about how Abeta is degraded and cleared following its secretion. We previously screened neuronal and nonneuronal cell lines for the production of proteases capable of degrading naturally secreted Abeta under biologically relevant conditions and concentrations. The major such protease identified was a metalloprotease released particularly by a microglial cell line, BV-2. We have now purified and characterized the protease and find that it is indistinguishable from insulin-degrading enzyme (IDE), a thiol metalloendopeptidase that degrades small peptides such as insulin, glucagon, and atrial natriuretic peptide. Degradation of both endogenous and synthetic Abeta at picomolar to nanomolar concentrations was completely inhibited by the competitive IDE substrate, insulin, and by two other IDE inhibitors. Immunodepletion of conditioned medium with an IDE antibody removed its Abeta-degrading activity. IDE was present in BV-2 cytosol, as expected, but was also released into the medium by intact, healthy cells. To confirm the extracellular occurrence of IDE in vivo, we identified intact IDE in human cerebrospinal fluid of both normal and Alzheimer subjects. In addition to its ability to degrade Abeta, IDE activity was unexpectedly found be associated with a time-dependent oligomerization of synthetic Abeta at physiological levels in the conditioned media of cultured cells; this process, which may be initiated by IDE-generated proteolytic fragments of Abeta, was prevented by three different IDE inhibitors. We conclude that a principal protease capable of down-regulating the levels of secreted Abeta extracellularly is IDE.

BACKGROUND

Measurement of B-type natriuretic peptide (BNP) concentration or its precursor (N-terminal fragment [NT-proBNP]) is recommended in patients with symptoms of left ventricular dysfunction and in other settings, but the relevance of these peptides to cardiovascular disease (CVD) in general populations or in patients with stable vascular disease is uncertain.

RESULTS

Data were collated from 40 long-term prospective studies involving a total of 87 474 participants and 10 625 incident CVD outcomes. In a comparison of individuals in the top third with those in the bottom third of baseline values of natriuretic peptides, the combined risk ratio (RR), adjusted for several conventional risk factors, was 2.82 (95% confidence interval [CI], 2.40 to 3.33) for CVD. Analysis of the 6 studies with at least 250 CVD outcomes (which should be less prone to selective reporting than are smaller studies) yielded an adjusted RR of 1.94 (95% CI, 1.57 to 2.39). RRs were broadly similar with BNP or NT-proBNP (RR, 2.89 [95% CI, 1.91 to 4.38] and 2.82 [95% CI, 2.35 to 3.38], respectively) and by different baseline vascular risk (RR, 2.68 [95% CI, 2.07 to 3.47] in approximately general populations; RR, 3.35 [95% CI, 2.38 to 4.72] in people with elevated vascular risk factors; RR, 2.60 [95% CI, 1.99 to 3.38] in patients with stable CVD). Assay of BNP or NT-proBNP in addition to measurement of conventional CVD risk factors yielded generally modest improvements in risk discrimination.

CONCLUSIONS

Available prospective studies indicate strong associations between circulating concentration of natriuretic peptides and CVD risk under a range of different circumstances. Further investigation is warranted, particularly in large general population studies, to clarify any predictive utility of these markers and to better control for publication bias.

In contrast to the earlier contention, adult humans have been shown recently to possess active brown adipose tissue with a potential of being of metabolic significance. Up to now, brown fat <em>precursor</em> cells have not been available for human studies. We have shown previously that human multipotent adipose-derived stem (hMADS) cells exhibit a normal karyotype and high self-renewal ability; they are known to differentiate into cells that exhibit the key properties of human white adipocytes, that is, uncoupling protein two expression, insulin-stimulated glucose uptake, lipolysis in response to <em>beta</em>-agonists and atrial <em>natriuretic</em> <em>peptide</em>, and release of adiponectin and leptin. Herein, we show that, upon chronic exposure to a specific PPARgamma but not to a PPAR<em>beta</em>/delta or a PPARalpha agonist, hMADS cell-derived white adipocytes are able to switch to a brown phenotype by expressing both uncoupling protein one (UCP1) and CIDEA mRNA. This switch is accompanied by an increase in oxygen consumption and uncoupling. The expression of UCP1 protein is associated to stimulation of respiration by <em>beta</em>-AR agonists, including <em>beta</em>3-AR agonist. Thus, hMADS cells represent an invaluable cell model to screen for drugs stimulating the formation and/or the uncoupling capacity of human brown adipocytes that could help to dissipate excess caloric intake of individuals.

The angiotensinogen M235T polymorphism in humans is linked to differential expression of the human angiotensinogen gene (AGT) gene and hypertension, but the homeostatic responses resulting from this polymorphism are not known. We therefore investigated how mice respond to five genetically determined levels of mouse angiotensinogen gene (Agt) expression covering the range associated with the M235T variants. By using high-throughput molecular phenotyping, tissue RNAs were assayed for expression of 10 genes important in hypertension. Significant positive and negative responses occurred in both sexes as Agt expression increased twofold, including a three-fold increase in aldosterone synthase expression in adrenal gland, and a two-fold decrease in renin expression in kidney. In males, cardiac expression of the precursor of atrial natriuretic peptide B and of adrenomedullin also increased approximately twofold. The relative expression of all genes studied except Agt differed significantly in the two sexes, and several unexpected relationships were encountered. A highly significant correlation between renal expression of the angiotensin type 1a receptor and kallikrein, independent of Agt genotype, is present in females (P < 0.0001) but not males (P = 0.4). The correlation between blood pressure (BP) and liver Agt expression within the five Agt genotypes is significant in females (P = 0.0005) but not in males (P = 0.2), whereas correlation of BP with differences between the genotypes is less in females (P = 0.06) than in males (P = 0.001). The marked gender differences in gene expression in wild-type mice and the changes induced by moderate alterations in Agt expression and BP emphasize the need to look for similar differences in humans.

BACKGROUND

Trimethylamine-N-oxide (TMAO) has been linked to increased cardiovascular risk. We aimed to determine the prognostic value of TMAO and its dietary precursors, choline and betaine, in heart failure (HF).

RESULTS

In 112 patients with chronic systolic HF with comprehensive echocardiographic evaluation, we measured plasma TMAO, choline, and betaine by mass spectrometry. Median (interquartile range) TMAO levels, choline, and betaine levels were 5.8 (3.6-12.1) μmol/L, 10.9 (8.4-14.0) μmol/L, and 43.8 (37.1-53.0) μmol/L, respectively, and were correlated with each other (all P < .0001 for both). TMAO levels were significantly higher in patients with diabetes mellitus (9.4 [4.9-13.2] vs 4.8 [3.4-9.8] μmol/L; P = .005) and in subjects with New York Heart Association functional class III or greater (7.0 [4.7-14.8] vs 4.7 [3.4-11.3] μmol/L; P = .02). Elevated TMAO, choline, and betaine levels were each associated with higher plasma N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels and more advanced left ventricular diastolic dysfunction, but not systolic dysfunction or inflammatory and endothelial biomarkers. Higher choline (hazard ratio [HR] 1.64, 95% CI 1.22-2.20; P = .001), betaine (HR 1.51, 95% CI 1.10-2.08; P = .01), and TMAO (HR 1.48, 95% CI 1.10-1.96; P = .01) predicted increased risk for 5-year adverse clinical events (death/transplantation). Only higher TMAO levels predicted incident adverse clinical events independently from age, estimated glomerular filtration rate, mitral E/septal Ea, and NT-proBNP levels (HR 1.46, 95% CI 1.03-2.14; P = .03).

CONCLUSIONS

Elevated plasma TMAO, choline, and betaine levels are each associated with more advanced left ventricular diastolic dysfunction and portend poorer long-term adverse clinical outcomes in chronic systolic HF. However, only higher plasma TMAO was associated with poor prognosis after adjustment for cardiorenal indices.

N-terminal natriuretic peptide type B (NT-proBNP) is a marker of cardiac dysfunction in light chain amyloidosis (AL) and a powerful prognostic determinant. Serum NT-proBNP and circulating free light chains (FLCs) were measured at enrollment and after 3 cycles of chemotherapy in 51 patients with cardiac AL. In patients (n = 22, 43%) in whom FLCs decreased by more than 50% (hematologic response), NT-proBNP concentration decreased by a median of 48%, whereas in the remaining patients it increased by 47% (P = .01). The reduction of NT-proBNP was greater in patients (n = 9) in whom amyloidogenic FLCs disappeared at immunofixation (median 53%), than in the remaining responding patients (median 31%, P = .04). Left ventricular wall thickness decreased by at least 2 mm in 3 of 20 patients in whom NT-proBNP improved. Fifteen patients died. Thirteen of them, in whom NT-proBNP and FLCs did not improve, died after a median of 1.8 months. The decrease of FLCs translates into a simultaneous decrease of NT-proBNP and improved survival. Patients in whom chemotherapy fails to induce such a decrease are at risk of early death. Cardiac function in AL can rapidly improve due to a reduction of the circulating amyloidogenic precursor, despite the amount of cardiac amyloid deposits remaining apparently unaltered, as measured by echocardiography.

BACKGROUND

Plasma renin concentrations are an important factor in cardiovascular risk profiling.

OBJECTIVE

To investigate the effects of sex, medication, and anthropometric factors that may contribute to the interindividual variation in the plasma concentrations of renin and its precursor prorenin.

METHODS

Prorenin and renin levels in 327 men and 383 women, aged 52-69 years, who participated in a 1994 reexamination of a previous population survey in Bavaria, were measured by immunoradiometric assay.

RESULTS

Prorenin and renin levels in men were significantly higher than those in women, those in women without estrogen replacement therapy were significantly higher than those in women with estrogen replacement therapy, and those in diabetics were significantly higher than those in nondiabetics. Prorenin level was correlated negatively to blood pressure and positively to age and the use of diuretics; it was normal in subjects using angiotensin converting enzyme inhibitors and beta-adrenergic antagonists (beta-blockers). Renin level was correlated negatively to atrial natriuretic peptide level and the use of beta-blockers, and it was elevated above normal levels in subjects using angiotensin converting enzyme inhibitors and diuretics as well as in subjects who had previously suffered myocardial infarction. After exclusion of data for women being administered estrogen replacement therapy, multivariate analysis revealed that sex (P<0.001), age (P<0.02), blood pressure (P<0.002), diabetes (P<0.05), and the use of angiotensin converting enzyme inhibitors (P<0.002), beta-blockers (P<0.001), and diuretics (P<0.05) were independent determinants of plasma prorenin. Plasma renin was independently related to atrial natriuretic peptide level (P<0.01) and the use of angiotensin converting enzyme inhibitors (P<0.001), beta-blockers (P<0.001), and diuretics (P<0.05).

CONCLUSIONS

These data demonstrate that there is a sexual dimorphism of prorenin levels in humans, suggesting that sex hormones affect the regulation of the renin gene. Data confirm previous reports of elevated prorenin levels in diabetics and older subjects, as well as of lower than normal prorenin levels in subjects with hypertension in smaller populations. Our findings may help to clarify the potential (patho)physiologic functions of prorenin and to identify the factors that influence the constitutive secretion and intracellular processing of this prohormone.

The biology of the natriuretic peptide (NP) system is complex, yet highly phylogenetically preserved. It regulates salt and water handling, promotes vasodilatation, and exerts favorable effects on the heart in the context of processes such as heart failure. Prior assumptions about the production of B-type NP (BNP) and its amino-terminal precursor fragment (NT-proBNP) have recently been refuted. It is now recognized that rather than a 1:1 secretion of these 2 NPs, a mixture of cleaved and uncleaved NPs is released by the cardiomyocyte. It is also recognized that BNP is rapidly modified into a mixture of various fragments. Commercial assays for the detection of BNP and NT-proBNP measure a mixture of cleaved and uncleaved NPs as well as varying amounts of degraded BNP. BNP and NT-proBNP are cleared differentially: BNP is actively removed from the bloodstream and also has passive clearance mechanisms, including renal clearance; NT-proBNP is cleared more passively by organs with high rates of blood flow, including the kidney.

Vitamin D analogs provide survival benefit for chronic kidney disease patients with cardiovascular complications. Activation of smooth muscle cells plays a role in cardiovascular diseases. It is not known how Vitamin D analogs modulate gene expression in smooth muscle cells. In this study, DNA microarray technology was used to assess the gene expression profile in human coronary artery smooth muscle cells treated with 0.1microM 1alpha,25-dihydroxyvitamin D3 (calcitriol) or paricalcitol (an analog of calcitriol) for 30 h. The effects of calcitriol and paricalcitol were similar. A total of 176 target genes were identified with 115 up-regulated and 61 down-regulated genes in the paricalcitol group. Target genes fall into various categories including cell differentiation/proliferation. Real-time RT-PCR analysis demonstrated that paricalcitol dose- and time-dependently regulated the expression of IGF1, WT1 and TGFbeta3, three genes known to modulate cell proliferation. Paricalcitol also down-regulated the expression of natriuretic peptide precursor B and thrombospondin 1. Both drugs inhibited cell proliferation in a dose-dependent manner. This study identified genes not previously known to be regulated by VDR, providing insight into understanding the role of VDR on regulating smooth muscle cell growth, thrombogenicity, fibrinolysis and endothelial regeneration.

OBJECTIVE

To compare head to head the diagnostic accuracy of B type natriuretic peptide (BNP) and the amino terminal fragment of its precursor hormone (NT-proBNP) for congestive heart failure (CHF) in an emergency setting.

METHODS

251 consecutive patients presenting to the emergency department with dyspnoea as a chief complaint were prospectively studied. Patients with acute coronary syndromes were excluded. The diagnosis of CHF was based on the Framingham score for CHF plus echocardiographic evidence of systolic or diastolic dysfunction. Blood concentrations of BNP and NT-proBNP were measured by two commercially available assays (Abbott and Roche methods). The diagnostic accuracies of BNP and NT-proBNP were assessed by receiver operating characteristic curve analysis.

RESULTS

Areas under the curve for BNP and NT-proBNP in patients with dyspnoea caused by CHF (n = 137) and in patients with dyspnoea attributable to other reasons (n = 114) did not differ significantly (area under the curve 0.916 v 0.903, p = 0.277, statistical power 94%). Cut off concentrations with the highest diagnostic accuracy were 295 ng/l for BNP (sensitivity 80%, specificity 86%, diagnostic accuracy 83%) and 825 ng/l for NT-proBNP (sensitivity 87%, specificity 81%, diagnostic accuracy 84%). Evaluation of discordant false classifications at these cut off concentrations showed no advantage for either BNP nor NT-proBNP in the biochemical diagnosis of CHF (17 misclassifications by BNP and 14 by NT-proBNP, p = 0.720). In the population studied, age, sex, and renal function had no impact on the diagnostic utility of both tests when compared by logistic regression models.

CONCLUSIONS

BNP and NT-proBNP may be equally useful as an aid in the diagnosis of CHF in short of breath patients presenting to the emergency department.

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.

BACKGROUND

B-type natriuretic peptide (BNP) and its N-terminal fragment (NT-proBNP) are the products of the enzyme-mediated cleavage of their precursor molecule, proBNP. The clinical significance of proBNP-derived peptides as biomarkers of heart failure has been explored thoroughly, whereas little is known about the mechanisms of proBNP processing. We investigated the role of 2 candidate convertases, furin and corin, in human proBNP processing.

METHODS

We measured proBNP expression in HEK 293 and furin-deficient LoVo cells. We used a furin inhibitor and a furin-specific small interfering RNA (siRNA) to explore the implication of furin in proBNP processing. Recombinant proBNPs were incubated with HEK 293 cells transfected with the corin-expressing plasmid. We applied mass spectrometry to analyze the products of furin- and corin-mediated cleavage.

RESULTS

Reduction of furin activity significantly impaired proBNP processing in HEK 293 cells. Furin-deficient LoVo cells were unable to process proBNP, whereas coexpression with furin resulted in effective proBNP processing. Mass spectrometric analysis revealed that the furin-mediated cleavage of proBNP resulted in BNP 1-32, whereas corin-mediated cleavage led to the production of BNP 4-32. Some portion of proBNP in the plasma of heart failure patients was not glycosylated in the cleavage site region and was susceptible to furin-mediated cleavage.

CONCLUSIONS

Both furin and corin are involved in the proBNP processing pathway, giving rise to distinct BNP forms. The significance of the presence of unprocessed proBNP in circulation that could be cleaved by the endogenous convertases should be further investigated for better understanding BNP physiology.

OBJECTIVE

This study sought to assess the prognostic impact of midregional pro-adrenomedullin (MR-proADM) after an acute myocardial infarction (AMI).

BACKGROUND

Adrenomedullin (ADM) is elevated in heart failure (HF) and after AMI. Another part of its precursor, MR-proADM, is more stable in circulation and ex vivo. We investigated the cardiovascular prognostic value after AMI of MR-proADM and compared it with N-terminal pro-B-type natriuretic peptide (NTproBNP), a marker of death and HF.

METHODS

We measured plasma MR-proADM and NTproBNP in 983 consecutive post-AMI patients (721 men, mean age 65.0 +/- 12.2 years), 3 to 5 days after chest pain onset.

RESULTS

There were 101 deaths and 49 readmissions with HF during follow-up (median 342, range 0 to 764 days). The MR-proADM was increased in patients with death or HF compared with survivors (median 1.19 nmol/l, range 0.09 to 5.39 nmol/l, vs. 0.71 nmol/l, range 0.25 to 6.66 nmol/l, p < 0.0001). Using a multivariate binary logistic model, log MR-proADM (odds ratio 4.22) and log NTproBNP (odds ratio 3.20) were significant independent predictors of death or HF (with creatinine, age, gender, and history of AMI). The areas under the receiver-operating characteristic curve for MR-proADM, NTproBNP, and the logistic model with both markers were 0.77, 0.79, and 0.84 respectively. Cox models for the predictors of death or HF showed the same variables (including log MR-proADM, hazard ratio 3.63; log NTproBNP, hazard ratio 2.67). The MR-proADM provided further risk stratification in those patients who had NTproBNP levels above the median (p < 0.0001). Findings were similar for death and HF as individual end points.

CONCLUSIONS

The ADM system is activated after AMI. The MR-proADM is a powerful predictor of adverse outcome, especially in those with an elevated NTproBNP. The MR-proADM may represent a clinically useful marker of prognosis after AMI.

Aging increases and caloric restriction (CR) decreases morbidity and mortality associated with the cardiovascular system. Using Affymetrix microarrays, we identified changes in heart gene expression induced by aging and CR in male mice. Eight weeks of CR (CR8) reproduced 19% of the long-term CR (LTCR)-related expression changes. Because CR8 begins to extend the life span of these mice, these genes may be keys to its cardioprotective effects. CR8 and LTCR changed gene expression in a manner consistent with reduced remodeling and fibrosis, and enhanced contractility and energy production via lipid beta-oxidation. Molecular and histochemical studies indicated that CR reduced natriuretic peptide precursor type B and collagen expression, and reduced perivascular collagen deposition. We found smaller cardiomyocytes in the left ventricle of old-LTCR mice, suggesting reduced age-related cell death. Eight weeks of control feeding returned 97% of the LTCR-responsive genes to control expression levels. Thus, key CR-induced effects are rapidly responsive to diet, suggesting reduced caloric intake has rapid, positive effects on the heart.

Human pro-B-type natriuretic peptide (proBNP), the precursor for B-type natriuretic peptide (BNP), was expressed in Chinese hamster ovary cells (CHO) and compared by Western blot analysis to BNP cross-reacting material immunoprecipitated from the plasma of heart failure patients. Both recombinant and native forms co-migrated as a diffuse band centered around 25 kDa and were reduced to a 12 kDa species by treatment with a mixture of O-link deglycosylation enzymes. The 108-amino acid CHO-expressed protein was examined by tryptic mapping and LC-MS and found to be an O-linked glycoprotein. Determination of the sites of O-glycosyl addition by blank cycle sequencing of tryptic and Glu-C (Staphylococcus aureus V8 protease) peptides showed that there are seven sites of glycosylation confined to a 36-amino acid residue stretch within the center of the propeptide region. This data is consistent with previous observations of higher molecular weight isoforms of BNP.

OBJECTIVE

The present study sought to evaluate the clinical utility of pro-B-type natriuretic peptides (proBNP) in patients admitted with acute decompensated heart failure.

BACKGROUND

Plasma natriuretic peptides (BNP(1-)(32), N-terminal [NT]-proBNP(1-76)) have been demonstrated to assist in the diagnosis of patients with heart failure. However, the precursor to these polypeptides (proBNP(1-108)) circulates in plasma and may interfere with the measurement of currently used biomarkers.

METHODS

Plasma natriuretic peptides were assessed in 164 individuals (99% men) hospitalized with decompensated heart failure. The B-type natriuretic peptide (BNP), NT-proBNP, and proBNP levels at hospital admission and discharge were compared with the incidence of cardiac death and all-cause mortality within 90 days post-discharge.

RESULTS

Pro-B-type natriuretic peptides demonstrated a high degree of correlation with both BNP (R = 0.924, p < 0.001) and NT-proBNP (R = 0.802, p < 0.001) at admission. Further characterization of proBNP demonstrated little variation with changes in age, body mass index, creatinine, or systolic dysfunction. All 3 plasma natriuretic peptides were significantly elevated at admission in patients suffering a cardiac death or all-cause mortality (p < 0.05). Receiver-operating characteristic curves demonstrated that admission and discharge NT-proBNP (area under the curve [AUC] 0.788 and AUC 0.834) had superior prognostic power for all-cause mortality when compared with BNP (AUC 0.644, p < 0.01 and AUC 0.709, p < 0.01) and proBNP (AUC 0.653, p < 0.01 and AUC 0.666, p < 0.01) at the same time points.

CONCLUSIONS

Admission values of all natriuretic peptides can be used to predict cardiac death and all-cause mortality. A preliminary comparison suggests that discharge values of NT-proBNP have the greatest diagnostic yield for predicting these end points. Further studies should explore the synergistic prognostic potential of all natriuretic peptides.

OBJECTIVE

Adrenomedullin (ADM) is a vasodilatory peptide. Its plasma levels or its precursors have not been evaluated in large populations of patients with chronic heart failure (CHF). We sought to explore mid-regional proADM (MR-proADM).

RESULTS

We assessed MR-proADM in 501 CHF patients [age 63 +/- 11 years, New York Heart Association (NYHA) class I/II/III/IV 9/44/39/8%, median N-terminal pro-B-type natriuretic peptide (NT-proBNP) 878 pg/mL (interquartile range-IQR 348-2480 pg/mL), median left ventricular ejection fraction (LVEF) 31% (IQR 25-37%)]. Mid-regional pro-adrenomedullin levels (median 0.64 nmol/L, IQR 0.49-0.87 nmol/L) increased with NYHA class (P < 0.0001). During 1-year follow-up, 70 patients (14%) died. Increasing MR-proADM was a predictor of poor survival at 12 months (hazard ratio 1.82, 95% confidence interval 1.24-2.66, P = 0.002) after multivariable adjustment. In receiver-operating characteristic curve analysis of 12-month survival, the area under the curve for MR-proADM and NT-proBNP was similar (P = 0.3). Comparison of Cox proportional hazard models using the likelihood ratio chi(2) statistic showed that both NT-proBNP and MR-proADM added prognostic value to a base model of LVEF, age, creatinine, and NYHA class. Adding MR-proADM to the base model had stronger prognostic power than adding NT-proBNP (both P < 0.01).

CONCLUSIONS

Mid-regional pro-adrenomedullin is an independent predictor of mortality in CHF patients, which adds prognostic information to NT-proBNP.

OBJECTIVE

Circulating fibroblast growth factor 23 (FGF23) is associated with adverse cardiovascular outcomes in CKD. Whether FGF23 predicts cardiovascular mortality after kidney transplantation, independent of measures of mineral metabolism and cardiovascular risk factors, is unknown.

METHODS

The association between plasma C-terminal FGF23 and cardiovascular mortality was analyzed in a single-center prospective cohort of 593 stable kidney transplant recipients (mean age ± SD, 52 ± 12 years; 54% male; estimated GFR, 47 ± 16 ml/min per 1.73 m(2)), at a median of 6.1 (interquartile range, 2.7-11.7) years after transplantation. Multivariate Cox regression models were built, adjusting for measures of renal function and mineral metabolism; Framingham risk factors; the left ventricular wall strain markers midregional fragment of pro-A-type natriuretic peptide (MR-proANP) and N-terminal-pro brain natriuretic peptide (NT-proBNP); and copeptin, the stable C-terminal portion of the precursor of vasopressin.

RESULTS

In multivariate linear regression analysis, MR-proANP (β=0.20, P<0.001), NT-proBNP (β=0.18, P<0.001), and copeptin (β=0.26, P<0.001) were independently associated with FGF23. During follow-up for 7.0 (interquartile range, 6.2-7.5) years, 128 patients (22%) died, of whom 66 (11%) died due to cardiovascular disease; 54 (9%) had graft failure. FGF23 was associated with an higher risk of cardiovascular mortality in a fully adjusted multivariate Cox regression model (hazard ratio [HR], 1.88 [95% confidence interval (CI), 1.11 to 3.19]; P=0.02). FGF23 was also independently associated with all-cause mortality (full model HR, 1.86 [95% CI, 1.27 to 2.73]; P=0.001). Net reclassification improved for both cardiovascular mortality (HR, 0.07 [95% CI, 0.01 to 0.14]; P<0.05) and all-cause mortality (HR, 0.11 [95% CI, 0.05 to 0.18]; P<0.001).

CONCLUSIONS

Plasma FGF23 is independently associated with cardiovascular and all-cause mortality after kidney transplantation. The association remained significant after adjustment for measures of mineral metabolism and cardiovascular risk factors.

This review focuses on the complex interactions between two major regulators of cardiac function; Ca2+ and stretch. Initial consideration is given to the effect of stretch on myocardial contractility and details the rapid and slow increases in contractility. These are shown to be related to two diverse changes in Ca2+ handling (enhanced myofilament Ca2+ sensitivity and increased intracellular Ca2+ transient, respectively). Interaction between stretch and Ca2+ is also demonstrated with respect to the rhythm of cardiac contraction. Stretch has been shown to alter action potential configuration, generate stretch-activated arrhythmias, and increase the rate of beating of the sino-atrial node. A variety of Ca(2+)-dependent mechanisms including attenuation of Ca2+ extrusion via Na+/Ca2+ exchange, Ca2+ entry through stretch-activated channels (SACs) and mobilisation of intracellular Ca2+ stores have been proposed to account for the effect of stretch on rhythm. Finally, the interaction between stretch and Ca2+ in the secretion of natriuretic peptides and onset of hypertrophy is discussed. Evidence is presented that Ca2+ (entering through L-type Ca2+ channels or SACs, or released from sarcoplasmic reticular stores) influences secretion of both atrial and B-type natriuretic peptide; there is data to support both positive and negative modulation by Ca2+. Ca2+ also appears to be important in the pathway that leads to expression of precursors of hypertrophic protein synthesis. In conclusion, two of the major regulators of cardiac muscle function, Ca2+ and stretch, interact to produce effects on the heart; in general these effects appear to be additive.

OBJECTIVE

This study sought to investigate plasma levels of circulating cardiac natriuretic peptides, atrial natriuretic peptide (ANP) and B-type or brain natriuretic peptide (BNP), in the general community, focusing on their relative differences in worsening human hypertension.

BACKGROUND

Although ANP and BNP are well-characterized regulators of blood pressure in humans, little is known at the population level about their relationship with hypertension. The authors hypothesized that hypertension is associated with a lack of activation of these hormones or their molecular precursors.

METHODS

The study cohort (N = 2,082, age >45 years) was derived from a random sample from Rochester, Minnesota, and each subject had a medical history, clinical examination, and assessment of different plasma forms of ANP and BNP. Patients were stratified by blood pressure. Multivariable linear regression was used to assess differences in natriuretic peptide levels in worsening hypertension.

RESULTS

Compared to normotensive, BNP(1-32) and N-terminal proBNP(1-76) (NT-proBNP(1-76)) were significantly decreased in pre-hypertension (p < 0.05), with BNP(1-32) significantly decreased in stage 1 as well (p < 0.05). Although proBNP(1-108) remained unchanged, the processed form was significantly increased only in stage 2 hypertension (p < 0.05). ANP(1-28) remained unchanged, while NT-ANP(1-98) was reduced in pre-hypertension (p < 0.05).

CONCLUSIONS

The authors demonstrated the existence of an impaired production and/or release of proBNP(1-108) along with a concomitant reduction of BNP(1-32) and NT-proBNP(1-76) in the early stages of hypertension, with a significant elevation only in stage 2 hypertension. Importantly, they simultaneously demonstrated a lack of compensatory ANP elevation in advanced hypertension.

OBJECTIVE

This study was designed to determine whether alternate pro-B-type natriuretic peptide (proBNP) and BNP forms circulate in the general population.

BACKGROUND

Bioactive BNP(1-32) and NT-proBNP(1-76) are derived from a precursor molecule, proBNP(1-108). Recent data suggest that aminodipeptidase-processed forms of BNP(1-32) (BNP(3-32)) and of proBNP(1-108) itself (proBNP(3-108)) may circulate and have additional diagnostic potential.

METHODS

Residents (age>> or =45 years) of Olmsted County, Minnesota, underwent medical review, echocardiography, and phlebotomy for 2 novel assays specific for proBNP(3-108) and BNP(3-32) and 2 commercial assays (Triage BNP and Roche NT-proBNP). Groups included normal subjects (n = 613), cardiovascular disease with normal ventricular function (n = 1,043), preclinical ventricular dysfunction (ALVD, n = 130), and chronic heart failure (HF, n = 52).

RESULTS

ProBNP(3-108) levels were above assay detection limits in 68% of normal subjects (50th; 25th to 75th percentiles: 7.85; 3.00 to 22.45 pmol/l) and correlated with age, gender, body size, and renal function and with results of commercial assays. ProBNP(3-108) levels were higher in ALVD (17.88; 6.07 to 42.76 pmol/l) or HF (42.75; 20.51 to 65.73 pmol/l), where they correlated more strongly with commercial assays. BNP(3-32) was above assay detection limits in 22% of normal subjects; levels were not correlated with age, body size, or renal function but were higher in HF. Neither novel assay was superior to commercial assays for the detection of ALVD or HF.

CONCLUSIONS

The presence of alternate circulating proBNP and BNP forms provides evidence for diverse proBNP and BNP processing in the general population. The physiologic consequences of these observations, both in terms of assay performance and endogenous BNP bioactivity, deserve further study.

BACKGROUND

Since the discovery of cardiac hormones almost 25 years ago, a vast amount of clinical research has identified the cardiac natriuretic peptides and their precursors as markers of heart failure. It even seems likely that the pro-B-type natriuretic peptide (proBNP)-derived peptides in plasma may become the most frequently measured peptides in the daily diagnosis and control of therapy. In contrast, the biochemistry of the peptides has received less attention.

METHODS

Published data available on the National Library of Medicine (NLM) were used as the basis for the review.

RESULTS

This review shows that the present understanding of the biochemistry of peptides is far from complete. In particular, cellular synthesis, including posttranslational precursor maturation, is poorly understood. Moreover, elimination of the precursor fragments is unknown. Elucidation of the molecular heterogeneity of proBNP products will therefore contribute to the understanding of the endocrine heart and may also have important diagnostic consequences. Above all, the different proBNP-derived peptides may not always be equal markers of the same pathophysiologic processes. A different metabolism and peripheral elimination may also impose new and peptide-specific limitations for diagnostic use.

CONCLUSIONS

It is necessary to focus more on the biology of the proBNP-derived peptides. In turn, new insight into the biochemistry could pave the way for more sensitive and disease-specific assays in the clinical setting.

BACKGROUND

Measurement of plasma concentrations of the biomarker copeptin may help identify patients with heart failure at high and low risk of mortality, although the value of copeptin measurement in elderly patients is not fully known.

OBJECTIVE

To evaluate the association between plasma concentrations of copeptin, a surrogate marker of vasopressin, combined with concentrations of the N-terminal fragment of the precursor to B-type natriuretic peptide (NT-proBNP), and mortality in a cohort of elderly patients with symptoms of heart failure.

METHODS

Primary health care population in Sweden enrolling 470 elderly patients with heart failure symptoms between January and December 1996. Clinical examination, echocardiography, and measurement of peptide concentrations were performed, with follow-up through December 2009.

METHODS

All-cause mortality and cardiovascular mortality.

RESULTS

After a median follow-up of 13 years, there were 226 deaths from all causes, including 146 deaths from cardiovascular causes. Increased concentration of copeptin was associated with increased risk of all-cause mortality (fourth quartile vs first quartile: 69.5% vs 38.5%, respectively; hazard ratio [HR], 2.04 [95% confidence interval {CI}, 1.38-3.02]) and cardiovascular mortality (fourth quartile vs first quartile: 46.6% vs 26.5%; HR, 1.94 [95% CI, 1.20-3.13]). The combination of elevated NT-proBNP concentrations and elevated copeptin concentrations also was associated with increased risk of all-cause mortality (copeptin fourth quartile: HR, 1.63 [95% CI, 1.08-2.47]; P = .01; NT-proBNP fourth quartile: HR, 3.17 [95% CI, 2.02-4.98]; P < .001). Using the 2 biomarkers simultaneously in the evaluation of cardiovascular mortality, there was a significant association for copeptin in the presence of NT-proBNP (log likelihood trend test, P = .048) and a significant association for NT-proBNP (fourth quartile: HR, 4.68 [95% CI 2.63-8.34]; P < .001).

CONCLUSIONS

Among elderly patients with symptoms of heart failure, elevated concentrations of copeptin and the combination of elevated concentrations of copeptin and NT-proBNP were associated with increased risk of all-cause mortality.

BACKGROUND

B-Type natriuretic peptide (BNP1-32) as well as the N-terminal fragment of the prohormone containing residues 1-76 (NT-proBNP1-76), both cleavage products of the precursor proBNP1-108, are reported to be powerful markers for prognosis and risk stratification of heart failure. However, the intact precursor also circulates in the bloodstream. Assays for the detection of these cleavage products have been developed, but most of these assays may overestimate the concentrations of the cleavage products because they also measure the precursor form. It is therefore important to develop an immunoassay that specifically measures solely proBNP1-108 in plasma.

METHODS

After carefully designing the peptide used to immunize mice, we selected a specific monoclonal antibody (mAb Hinge76) that recognizes the cleavage site of proBNP1-108, an epitope present only in the precursor form. mAb Hinge76 recognizes recombinant proBNP1-108 in a dose-dependent manner, without any significant cross-reactivity with either recombinant NT-proBNP1-76 or synthetic BNP1-32. By combining mAb Hinge76 with a polyclonal antibody directed against BNP1-32, we were able to set up a proBNP1-108-specific sandwich immunoassay able to confirm the presence of proBNP1-108 in blood samples.

RESULTS

From a cohort of 50 healthy persons and 170 patients with congestive heart failure (CHF), our assay was able to differentiate healthy individuals from CHF patients (P <0.005). Interestingly, plasma proBNP1-108 concentrations were correlated with New York Heart Association classification. Moreover, a close relationship between proBNP1-108 and BNP1-32 concentrations may exist, as a good correlation (r2= 0.89) was obtained when their respective concentrations were compared.

CONCLUSIONS

mAb Hinge76 is the first proBNP1-108-specific mAb produced that allows accurate estimation of proBNP1-108 concentrations in plasma.