Enhanced brain natriuretic peptide response to peak exercise in heart transplant recipients

The Endocrine Function of the Heart: Physiology and Involvements of Natriuretic Peptides and Cyclic Nucleotide Phosphodiesterases in Heart Failure

Besides pumping, the heart participates in hydro-sodium homeostasis and systemic blood pressure regulation through its endocrine function mainly represented by the large family of natriuretic peptides (NPs), including essentially atrial natriuretic (ANP) and brain natriuretic peptides (BNP). Under normal conditions, these peptides are synthesized in response to atrial cardiomyocyte stretch, increase natriuresis, diuresis, and vascular permeability through binding of the second intracellular messenger’s guanosine 3′,5′-cyclic monophosphate (cGMP) to specific receptors. During heart failure (HF), the beneficial effects of the enhanced cardiac hormones secretion are reduced, in connection with renal resistance to NP. In addition, there is a BNP paradox characterized by a physiological inefficiency of the BNP forms assayed by current methods. In this context, it appears interesting to improve the efficiency of the cardiac natriuretic system by inhibiting cyclic nucleotide phosphodiesterases, responsible for the degradation of cGMP. Recent data support such a therapeutic approach which can improve the quality of life and the prognosis of patients with HF.

Pretreatment with brain natriuretic peptide reduces skeletal muscle mitochondrial dysfunction and oxidative stress after ischemia-reperfusion

Brain natriuretic peptide (BNP) reduces the extent of myocardial infarction. We aimed to determine whether BNP may reduce skeletal muscle mitochondrial dysfunctions and oxidative stress through mitochondrial K(ATP) (mK(ATP)) channel opening after ischemia-reperfusion (IR). Wistar rats were assigned to four groups: sham, 3-h leg ischemia followed by 2-h reperfusion (IR), pretreatment with BNP, and pretreatment with 5-hydroxydecanoic acid, an mK(ATP) channel blocker, before BNP. Mitochondrial respiratory chain complex activities of gastrocnemius muscles were determined using glutamate-malate (V(max)), succinate (V(succ)), and N,N,N',N'-tetramethyl-p-phenylenediamine dihydrochloride ascorbate (V(TMPD/asc)). Apoptosis (Bax-to-Bcl2 mRNA ratio and caspase-3 activity) and oxidative stress (dihydroethidium staining) were also assessed. Compared with the sham group, IR significantly decreased V(max), reflecting complex I, II, and IV activities (-36%, 3.7 ± 0.3 vs. 5.8 ± 0.2 μmol O(2)·min(-1)·g dry wt(-1), P < 0.01), and V(TMPD/asc), reflecting complex IV activity (-37%, 8.6 ± 0.8 vs. 13.7 ± 0.9 μmol O(2)·min(-1)·g dry wt(-1), P < 0.01). IR increased Bax-to-Bcl2 ratio (+57%, 1.1 ± 0.1 vs. 0.7 ± 0.1, P < 0.05) and oxidative stress (+45%, 9,067 ± 935 vs. 6,249 ± 723 pixels, P > 0.05). BNP pretreatment reduced the above alterations, increasing V(max) (+38%, P < 0.05) and reducing Bax-to-Bcl2 ratio (-55%, P < 0.01) and oxidative stress (-58%, P < 0.01). BNP protection against deleterious IR effects on skeletal muscles was abolished by 5-hydroxydecanoic acid. Caspase-3 activities did not change significantly. Conversely, BNP injected during ischemia failed to protect against muscle injury. In addition to maintaining the activity of mitochondrial respiratory chain complexes and possibly decreasing apoptosis, pretreatment with BNP protects skeletal muscle against IR-induced lesions, most likely by decreasing excessive production of radical oxygen species and opening mK(ATP) channels.

L-arginine supplementation improves exercise capacity after a heart transplant

BACKGROUND

Endothelial dysfunction is associated with the decreased exercise capacity observed in heart-transplant (HTx) recipients. L-arginine supplementation (LAS) stimulates the nitric oxide (NO) pathway and restores endothelial function.

OBJECTIVE

We compared exercise capacity in healthy subjects and HTx patients and investigated whether chronic LAS might improve exercise capacity and NO/endothelin balance after an HTx.

DESIGN

Clinical, echocardiographic, and exercise characteristics were measured in 11 control subjects and 22 HTx recipients. In a prospective, double-blind study, the 22 HTx recipients performed a 6-min exercise [6-min-walk test (6MWT)] and a maximal bicycle exercise test before and after a 6-wk period of placebo intake or LAS. Endothelial function was measured by analyzing blood NO metabolites, endothelin, and the resulting NO/endothelin balance.

RESULTS

Exercise capacity decreased after transplantation. Unlike with the placebo intake, 6 wk of LAS improved quality of life in HTx recipients (mean +/- SEM Minnesota Score: from 15.3 +/- 1.3 to 10.6 +/- 1.1; P < 0.001) and their submaximal exercise capacity. The distance walked during the 6MWT increased (from 525 +/- 20 to 580 +/- 20 m; P = 0.002), and the ventilatory threshold during the incremental test was delayed by 1.2 min (P = 0.01). Central factors such as resting stroke volume, systolic pulmonary arterial pressure, cardiac systolodiastolic functions, and heart-rate reserve were not modified, but LAS significantly increased the NO:endothelin ratio (from 2.49 +/- 0.38 to 3.31 +/- 0.39; P = 0.03).

CONCLUSION

Oral LAS may be a useful adjuvant therapeutic to improve quality of life and exercise tolerance in HTx recipients.

Brain natriuretic peptide in pulmonary arterial hypertension: biomarker and potential therapeutic agent

B-type natriuretic peptide (BNP) is a member of the natriuretic peptide family, a group of widely distributed, but evolutionarily conserved, polypeptide mediators that exert myriad cardiovascular effects. BNP is a potent vasodilator with mitogenic, hypertrophic and pro-inflammatory properties that is upregulated in pulmonary hypertensive diseases. Circulating levels of BNP correlate with mean pulmonary arterial pressure (mPAP) and pulmonary vascular resistance (PVR) in patients with pulmonary arterial hypertension (PAH). Elevated plasma BNP levels are associated with increased mortality in patients with PAH and a fall in BNP levels after therapy is associated with improved survival. These findings have important clinical implications in that a noninvasive blood test may be used to identify PAH patients at high-risk of decompensation and to guide pulmonary vasodilator therapy. BNP also has several biologic effects that could be beneficial to patients with PAH. However, lack of a convenient method for achieving sustained increases in circulating BNP levels has impeded the development of BNP as a therapy for treating pulmonary hypertension. New technologies that allow transdermal or oral administration of the natriuretic peptides have the potential to greatly accelerate research into therapeutic use of BNP for cor pulmonale and pulmonary vascular diseases. This review will examine the basic science and clinical research that has led to our understanding of the role of BNP in cardiovascular physiology, its use as a biomarker of right ventricular function and its therapeutic potential for managing patients with pulmonary vascular disease.

Does circulating BNP normalize after heart transplantation in patients with normal hemodynamic and right and left heart functions?

BACKGROUND

Increased brain natriuretic peptide (BNP) in cardiovascular disease is thought to be a compensatory protective mechanism allowing to delay the occurrence of terminal heart failure. Heart transplantation should normalize the neuroendocrine balance but BNP remains elevated in stable heart-transplant recipients (Htx). Such increase has been related to persistent endothelial and cardiac dysfunctions. The purpose of this study was to determine whether selected Htx, presenting with normal hemodynamic and cardiac systolic and diastolic functions on both side of the heart, show a normalization of their BNP plasma values.

METHODS

Of a cohort of well-being 26 Htx, we selected 12 patients with normal hemodynamics and left and right heart systolic and diastolic functions and compared their circulating BNP, cyclic guanosine monophosphate (cGMP) (the BNP second messenger) and endothelin-1 (ET) values with that of 12 age-, body mass index- and mean arterial pressure-matched controls. Cardiac function determination by echodoppler included cardiac filling pressures assessment using tissue Doppler imaging. Blood samples for biological and hormonal determinations were drawn at rest, within 15 min before echocardiography.

RESULTS

As selected, hemodynamic and left and right heart systolic and diastolic functions were located in the normal range in Htx. Plasma ET value was also similar in Htx and controls (20.7 +/- 0.9 vs. 19.6 +/- 0.9 fmol/mL). However, circulating BNP, like cGMP, was still significantly increased after heart transplantation, when compared with controls (33.8 +/- 8.5 vs. 4.0 +/- 0.9 pg/mL, p = 0.002 and 8.2 +/- 1.1 vs. 4.4 +/- 0.3 nmol/L, p = 0.003) for BNP and cGMP, respectively, in Htx and controls. Interestingly, the sole correlation observed was between BNP and cGMP (r = 0.85, p < 0.0001) after heart transplantation.

CONCLUSIONS

After heart transplantation, BNP remained increased despite the normalization of hemodynamic and cardiac systolic and diastolic functions. This suggests that such endocrine heart stimulation should not be viewed only as a hemodynamic marker in Htx. Further studies will be useful to investigate the role of pro-inflammatory cytokines and whether elevated BNP still possesses antifibrotic properties, further supporting the interest of enhancing its activity after heart transplantation.

Exercise limitation in trained heart and kidney transplant recipients: central and peripheral limitations

BACKGROUND

To evaluate the role of central and peripheral contributions to exercise limitation after transplantation, we compared, during exercise, 2 groups of very well-trained heart transplants recipients (HTRs) and kidney transplant recipients (KTRs) with a group of control subjects (CSs), matched for physical level.

METHODS

Nineteen male subjects, 7 HTRs, 6 KTRs and 6 CSs, participated in the study. All transplant patients were in sinus rhythm and were matched for immunosuppressive therapy, none of whom had therapy with chronotropic effects. Exercise capacities were evaluated using a symptom-limited treadmill test. Oxygen consumption (VO2) and heart rate (HR) were measured continuously. Heart rate reserve (HRR) was defined as peak HR minus resting HR; resting HR was the stabilized HR measured in the supine position before the treadmill test.

RESULTS

Functional capacities were evaluated for all HTRs, KTRs and CSs, according to maximal VO2 (41.5 +/- 4.0, 52.0 +/- 8.7 and 50.6 +/- 9.0 ml/kg per min, respectively), maximal treadmill speed (9.9 +/- 1.2, 12.7 +/- 1.9 and 15.5 +/- 1.5 km/h) and HRR (65 +/- 17, 101 +/- 12 and 110 +/- 11 beats per minute [bpm]), which were significantly lower in the HTR group (p < 0.05). Regardless of type of organ transplant, both HTR and KTR patients had a similar VO2/treadmill speed relationship, significantly higher than in the CS group. HRR correlated with maximal VO2 for HTRs (r = 0.72, p < 0.05).

CONCLUSIONS

Despite regular training, the decreased mechanical efficiency reflected by an increased VO2/treadmill speed relationship suggests a peripheral limitation in both heart and kidney transplant patients. Furthermore, exercise limitations in HTRs likely arose from both central and peripheral factors, in view of their specific HRR reduction. These factors probably contributed to the decreased speed and VO2 observed in the HTR group.

Determinants of B-type natriuretic peptide plasma levels in the chronic phase after heart transplantation*

Determinants of B-type natriuretic peptide (BNP) plasma levels in the chronic phase after heart transplantation remain unclear. BNP was measured in 105 stable long-term heart transplant recipients with normal left ventricular function by echocardiography and correlated with clinical, demographic and hemodynamic parameters. Multivariate analysis revealed a significant correlation of BNP with female recipient gender (P = 0.006), time post-transplant (P =0.006), donor age (P = 0.007), angiographic signs of transplant vasculopathy (TVP) (P = 0.03), serum creatinine level (P = 0.04), and a strong trend for diastolic dysfunction (P = 0.09). Donor gender, recipient age, cyclosporin A blood levels, rejection history, and pulmonary artery pressure had no independent effect on BNP. BNP after heart transplantation appears to be influenced both by established general determinants (female gender, renal function) and transplant-specific determinants such as time post-transplant, donor age and potentially also TVP. In order to determine the value of BNP as a potential surrogate marker of TVP serial intraindividual measurements appear appropriate.

Usefulness of B-type natriuretic peptide as a noninvasive screening tool for cardiac allograft pathology in pediatric heart transplant recipients

We examined the utility of B-type natriuretic peptide (BNP) in the evaluation of pediatric orthotopic heart transplant recipients for allograft pathology by measuring the serum BNP levels at the time of either screening echocardiography and biopsy, or at the time of clinical rejection. There was a significant difference (p <0.0001) in the BNP levels in 37 patients in the group with evidence of pathology compared with those without evidence. There was also 100% sensitivity and 100% negative predictive value of BNP levels >100 pg/ml for identifying graft pathology.

Exercise after heart transplantation

Exercise intolerance in heart transplant recipients (HTR) has a multifactorial origin, involving complex interactions among cardiac, neurohormonal, vascular, skeletal muscle and pulmonary abnormalities. However, the role of these abnormalities may differ as a function of time after transplantation and of many other variables. The present review is aimed at evaluating the role of cardiac, pulmonary and muscular factors in limiting maximal aerobic performance of HTR, and the benefits of chronic exercise. Whereas pulmonary function does not seem to affect gas exchange until a critical value of diffusing lung capacity is attained, cardiac and skeletal muscle function deterioration may represent relevant factors limiting maximal and submaximal aerobic performance. Cardiac function is mainly limited by chronotropic incompetence and diastolic dysfunction, whereas muscle activity seems to be limited by impaired oxygen supply as a consequence of the reduced capillary network. The latter may be due to either immunosuppressive regimen or deconditioning. Endurance and strength training may greatly improve muscle function and maximal aerobic performance of HTR, and may also reduce side effects of immunosuppressive therapy and control risk factors for cardiac allograft vasculopathy. For the above reasons exercise should be considered an important therapeutic tool in the long-term treatment of heart transplant recipients.

Mechanisms of renal hyporesponsiveness to ANP in heart failure

The atrial natriuretic peptide (ANP) plays an important role in chronic heart failure (CHF), delaying the progression of the disease. However, despite high ANP levels, natriuresis falls when CHF progresses from a compensated to a decompensated state, suggesting emergence of renal resistance to ANP. Several mechanisms have been proposed to explain renal hyporesponsiveness, including decreased renal ANP availability, down-regulation of natriuretic peptide receptors and altered ANP intracellular transduction signal. It has been demonstrated that the activity of neutral endopeptidase (NEP) is increased in CHF, and that its inhibition enhances renal cGMP production and renal sodium excretion. In vitro as well as in vivo studies have provided strong evidence of an increased degradation of intracellular cGMP by phosphodiesterase in CHF. In experimental models, ANP-dependent natriuresis is improved by phosphodiesterase inhibitors, which may arise as new therapeutic agents in CHF. Sodium-retaining systems likely contribute to renal hyporesponsiveness to ANP through different mechanisms. Among these systems, the renin-angiotensin-aldosterone system has received particular attention, as angiotensin II and ANP have renal actions at the same sites and inhibition of angiotensin-converting enzyme and angiotensin-receptor blockade improve ANP hyporesponsiveness. Less is known about the interactions between the sympathetic nervous system, endothelin or vasopressin and ANP, which may also blunt ANP-induced natriuresis. To summarize, renal hyporesponsiveness to ANP is probably multifactorial. New treatments designed to restore renal ANP efficiency should limit sodium retention in CHF patients and thus delay the progression to overt heart failure.

Usefulness of B-type natriuretic peptide levels in predicting hemodynamic perturbations after heart transplantation despite preserved left ventricular systolic function

The aim of this prospective study was to evaluate the association of peripheral B-type natriuretic peptide (BNP) levels with clinical symptoms and central hemodynamic and echocardiographic measures in cardiac transplantation. BNP reflects ventricular wall stress and correlates with severity of heart failure. No previous investigation has comprehensively assessed the rapid bedside BNP assay for predicting hemodynamic measures of cardiac allograft function in heart transplantation. We evaluated BNP levels using a rapid point-of-care assay in 87 stable cardiac transplant recipients who had 237 consecutive measurements along with endomyocardial biopsy, right-sided cardiac catheterization, and echocardiography. Using median tendencies, 2 groups were identified: the low BNP group (n = 116, BNP <150 pg/ml) and the high BNP group (n = 121, BNP >/=150 pg/ml). The high BNP group had increased right atrial pressures, higher pulmonary artery systolic pressures, pulmonary capillary wedge pressures, and lower cardiac index. Besides hemodynamic variables, the presence of right ventricular dysfunction (p = 0.05) and significant tricuspid regurgitation (p = 0.003) were associated with higher BNP levels. Independent predictors of BNP levels on multivariate analysis included elevated pulmonary capillary wedge pressure, lower cardiac index, and symptoms of dyspnea and fatigue. This initial investigation establishes the accuracy of a point-of-care BNP assay in predicting cardiopulmonary hemodynamic aberrations despite preserved left ventricular systolic function in heart transplant recipients. Rapid bedside BNP analysis may provide a noninvasive surrogate method for the comprehensive assessment of cardiac allograft function and hemodynamics in heart transplantation.

Hormonal, renal, hemodynamic responses to acute neutral endopeptidase inhibition in heart transplant patients

We investigated the hemodynamic, renal, and hormonal responses to neutral endopeptidase (NEP) inhibition during a 6-h, double-blind, randomized, placebo-controlled study in seven chronic, stable heart transplant patients. Baseline characteristics were similar during both experiments, and no significant changes were observed after placebo. NEP inhibition increased circulating endothelin-1 (from 2.01 +/- 0.1 to 2.90 +/- 0.2 pmol/l; P < 0.01), atrial natriuretic peptide (ANP; from 21.5 +/- 2.7 to 29.6 +/- 3.7 pmol/l; P < 0.01), and the ANP second messenger cGMP. Noteworthy, systemic blood pressure did not increase. Renal plasma flow and glomerular filtration rate remained unmodified after NEP inhibition. Filtration fraction (33 +/- 13%), diuresis (196 +/- 62%), and natriuresis (315 +/- 105%) increased significantly in relation to ANP and cGMP. A strong inverse relationship was observed between excreted cGMP and sodium reabsorption (r = -0.71, P < 0.0001). Thus, despite significantly increasing endothelin-1, NEP inhibition did not adversely influence systemic or renal hemodynamics in transplant patients. ANP, possibly through a tubular action, enhances the natriuresis observed after NEP inhibition.

Stability of B-type natriuretic peptide levels during exercise in patients with congestive heart failure: implications for outpatient monitoring with B-type natriuretic peptide

BACKGROUND

B-natriuretic peptide (BNP), a neurohormone secreted from the cardiac ventricles, reflects left ventricular pressure and correlates to disease severity and prognosis. The fact that BNP levels can now be measured by a rapid assay suggests its potential usefulness in the outpatient clinic. However, if patient activity were to markedly alter BNP levels, its use would be less attractive for monitoring patients in the outpatient clinical setting.

METHODS

A total of 30 patients (10 normal, 10 New York Heart Association [NYHA] class I-II, 10 NYHA class III-IV) exercised with an upright bicycle protocol. Exercise was carried out to 75% of maximum heart rate, and venous blood was sampled before, immediately after, and 1 hour after completion of exercise. Plasma levels of BNP, epinephrine, and norepinephrine were measured.

RESULTS

BNP levels at baseline were 29 +/- 11 pg/mL for normal subjects, 126 +/- 26 pg/mL for NYHA I-II subjects, and 1712 +/- 356 pg/mL for NYHA III-IV subjects. The change in BNP levels with exercise was significantly lower than the change in epinephrine and norepinephrine (P <.001). In normal subjects, BNP increased from 29 pg/mL to 44 pg/mL with peak exercise, still within the range of normal (<100 pg/mL). This is compared with larger increases of norepinephrine (716 pg/mL to 1278 pg/mL) and epinephrine (52 pg/mL to 86 pg/mL) with exercise in normal subjects. There were also only small increases in BNP with exercise in patients with congestive heart failure (NYHA I-II, 30%; NYHA III-IV, 18%). For the same groups, epinephrine levels increased by 218% and 312%, respectively, and norepinephrine levels increased by 232% and 163%, respectively. One hour after completion of exercise, there were only minimal changes in BNP levels from baseline state in normal subjects (+0.9%) and patients with NYHA I-II (3.8%). In patients with NYHA III-IV, there was a 15% increase from baseline 1 hour after exercise.

CONCLUSIONS

BNP levels show only minor changes with vigorous exercise, making it unlikely that a normal patient would be classified as having congestive heart failure based on a BNP level obtained after activity. Prior activity should not influence BNP levels in patients with congestive heart failure. Therefore, when a patient presents to clinic with a marked change in their BNP level, it may reflect a real change in their condition.

Cardiac natriuretic peptides--hope or hype?

In recent years, biomedical science has witnessed the emergence of peptide biochemicals as significant topics of research. Some of these peptides are of little potential clinical use, while others, of which cardiac natriuretic peptides are an example, appear to be promising. This particular group of peptides (i.e. ANP, BNP and CNP) shows promising diagnostic as well as therapeutic potential for various pathological conditions. In the case of acute myocardial infarction, these peptides have significant diagnostic and predictive properties, more so than other biochemicals such as adrenaline, renin and aldosterone. In addition, ANP is found to have significant benefits over the classical anti-anginal drug glyceryl trinitrate. However, as is the case with other peptides, applying these benefits clinically may not be easy because of the structure of the compounds, but various strategies are now being applied to solve this problem. These include the use of non-peptide receptor ligands, inhibitors of ANP metabolism, gene therapy and so on. The development of drugs in clinical practice, which exploits the natriuretic peptides system therefore seems to be promising, and this article reviews advances in our understanding of these compounds.