Autocrine/paracrine determinants of strain-activated brain natriuretic peptide gene expression in cultured cardiac myocytes

Left Ventricular Mass Index Predicts Renal Function Decline in Patients with Chronic Kidney Disease

Background and Objectives: Several studies revealed a relation between abnormal cardiac remodeling and glomerular filtration rate (GFR) decline, but there are limited data regarding echocardiographic changes in chronic kidney disease (CKD). This study evaluated the abnormal cardiac structures characterizing patients with CKD, assessing the independent association between echocardiographic parameters and the risk of decline in renal function. Materials and Methods: In total, 160 patients with CKD were studied. All patients underwent an echocardiographic exam and 99mTc-DTPA renal scintigraphy to measure the GFR. After the baseline assessments, patients were followed prospectively for 12 months, or until the endpoint achievement, defined as a worsening in renal function (doubling of baseline serum creatinine, GFR decline ≥25%, the start of dialysis). Results: Patients with GFR values of 34.8 ± 15 mL/min, identifying stages III-IV of CKD, were associated with high levels of left ventricular mass index (LVMi) (101.9 ± 12.2 g/m2), which was related to proteinuria, systolic blood pressure, and pulmonary artery systolic pressure in a multiple regression model. During the observational period, 26% of patients reached the endpoint. Regression analysis revealed LVMi as a predictor of change in renal function after adjusting for kidney and cardiac risk factors. Multiple Cox regression indicated that an increase in LVMi was associated with a 12% increased risk of kidney disease progression (HR: 1.12; 95% CI: 1.04-1.16; p = 0.001). Conclusions: In patients with CKD, high LVMi represents an independent predictor of the progressive decline of the renal function, until the start of renal replacement therapy. Echocardiography can help identify patients at high risk for renal disease worsening in patients with CKD independently of clinical cardiac involvement.

Cannabinoid receptor agonist attenuates angiotensin II-induced enlargement and mitochondrial dysfunction in rat atrial cardiomyocytes

Pathological remodeling of atrial tissue renders the atria more prone to arrhythmia upon arrival of electrical triggers. Activation of the renin-angiotensin system is an important factor that contributes to atrial remodeling, which may result in atrial hypertrophy and prolongation of P-wave duration. In addition, atrial cardiomyocytes are electrically coupled via gap junctions, and electrical remodeling of connexins may result in dysfunction of coordinated wave propagation within the atria. Currently, there is a lack of effective therapeutic strategies that target atrial remodeling. We previously proposed that cannabinoid receptors (CBR) may have cardioprotective qualities. CB13 is a dual cannabinoid receptor agonist that activates AMPK signaling in ventricular cardiomyocytes. We reported that CB13 attenuates tachypacing-induced shortening of atrial refractoriness and inhibition of AMPK signaling in the rat atria. Here, we evaluated the effects of CB13 on neonatal atrial rat cardiomyocytes (NRAM) stimulated by angiotensin II (AngII) in terms of atrial myocyte enlargement and mitochondrial function. CB13 inhibited AngII-induced enhancement of atrial myocyte surface area in an AMPK-dependent manner. CB13 also inhibited mitochondrial membrane potential deterioration in the same context. However, AngII and CB13 did not affect mitochondrial permeability transition pore opening. We further demonstrate that CB13 increased Cx43 compared to AngII-treated neonatal rat atrial myocytes. Overall, our results support the notion that CBR activation promotes atrial AMPK activation, and prevents myocyte enlargement (an indicator that suggests pathological hypertrophy), mitochondrial depolarization and Cx43 destabilization. Therefore, peripheral CBR activation should be further tested as a novel treatment strategy in the context of atrial remodeling.

Comparison of Outcomes After Ablation of Atrial Fibrillation in Patients With Heart Failure With Preserved Versus Reduced Ejection Fraction

Catheter ablation improves outcomes in atrial fibrillation (AF) patients with heart failure (HF) with reduced ejection fraction (HFrEF). We sought to evaluate the efficacy and safety of catheter ablation of AF in HF patients with a preserved ejection fraction (HFpEF). We performed a retrospective study of all patients who underwent de novo radiofrequency catheter ablation enrolled in the UC San Diego AF Ablation Registry. The primary outcome was recurrence of all atrial arrhythmias on or off antiarrhythmic drugs (AAD). Of 547 total patients, 51 (9.3%) had HFpEF, 40 (7.3%) had HFrEF, and 456 (83.4%) were without HF. There was no difference in recurrence of atrial arrhythmias on or off AAD (Adjusted Hazard Ratio [AHR] 1.92 [95% CI 0.97 to 3.83] for HFpEF vs HFrEF and AHR 0.90 [95% CI 0.59 to 1.39] for HFpEF vs no HF) or off AAD (AHR 1.96 [95% CI 0.99 to 3.90] for HFpEF vs HFrEF and AHR 1.14 [95% CI 0.74 to 1.77] for HFpEF vs no HF). There was also no difference in rates of all-cause hospitalizations (AHR 1.80 [95% CI 0.97 to 3.33] for HFpEF vs HFrEF and AHR 2.05 [95% CI 1.30 to 3.23] for HFpEF vs no HF) or rates of all-cause mortality (AHR 0.53 [95% CI 0.05 to 6.11] for HFpEF vs HFrEF and AHR 2.46 [95% CI 0.34 to 17.92] for HFpEF vs no HF). There were no significant differences in AAD use (p = 0.176) or procedural complications between groups (p = 0.980). In conclusion, there were no significant differences in arrhythmia-free survival between patients with HFpEF and HFrEF that underwent catheter ablation of AF.

Association of B-Type Natriuretic Peptide Level With Residual Kidney Function in Incident Peritoneal Dialysis Patients

BACKGROUND

Residual kidney function (RKF) is an important factor influencing both technique and patient survival in peritoneal dialysis (PD) patients. B-type natriuretic peptide (BNP) is considered a marker of cardio-renal syndrome. The relationship between BNP and RKF in PD patients remains unclear.

METHODS

We conducted a prospective study of 89 patients who had started and continued PD for 6 months or more in Kyushu University Hospital between June 2006 and September 2015. Participants were divided into low BNP (≤ 102.1 ng/L) and high BNP (> 102.1 ng/L) groups according to median plasma BNP level at PD initiation. The primary outcome was RKF loss, defined as 24-hour urine volume less than 100 mL. We estimated the association between BNP and RKF loss using a Kaplan-Meier method and Cox proportional hazards model and compared the rate of RKF decline between the 2 groups. To evaluate the consistency of the association, we performed subgroup analysis stratified by baseline characteristics.

RESULTS

During the median follow-up of 30 months, 30 patients lost RKF. Participants in the high BNP group had a 5.87-fold increased risk for RKF loss compared with the low BNP group after adjustment for clinical and cardiac parameters. A high plasma BNP level was more clearly associated with RKF loss in younger participants compared with older participants in subgroup analysis.

CONCLUSIONS

B-type natriuretic peptide may be a useful risk marker for RKF loss in PD patients. The clinical importance of plasma BNP level as a marker of RKF loss might be affected by age.

Mechanical stretch induced transcriptomic profiles in cardiac myocytes

Mechanical forces are able to activate hypertrophic growth of cardiomyocytes in the overloaded myocardium. However, the transcriptional profiles triggered by mechanical stretch in cardiac myocytes are not fully understood. Here, we performed the first genome-wide time series study of gene expression changes in stretched cultured neonatal rat ventricular myocytes (NRVM)s, resulting in 205, 579, 737, 621, and 1542 differentially expressed (>2-fold, P < 0.05) genes in response to 1, 4, 12, 24, and 48 hours of cyclic mechanical stretch. We used Ingenuity Pathway Analysis to predict functional pathways and upstream regulators of differentially expressed genes in order to identify regulatory networks that may lead to mechanical stretch induced hypertrophic growth of cardiomyocytes. We also performed micro (miRNA) expression profiling of stretched NRVMs, and identified that a total of 8 and 87 miRNAs were significantly (P < 0.05) altered by 1-12 and 24-48 hours of mechanical stretch, respectively. Finally, through integration of miRNA and mRNA data, we predicted the miRNAs that regulate mRNAs potentially leading to the hypertrophic growth induced by mechanical stretch. These analyses predicted nuclear factor-like 2 (Nrf2) and interferon regulatory transcription factors as well as the let-7 family of miRNAs as playing roles in the regulation of stretch-regulated genes in cardiomyocytes.

Atrial Fibrillation and Heart Failure - Cause or Effect?

There are emerging epidemics of atrial fibrillation (AF) and heart failure in most developed countries, with a significant health burden. Due to many shared pathophysiological mechanisms, which facilitate the maintenance of each condition, AF and heart failure co-exist in up to 30% of patients. In the circumstance where known structural causes of heart failure (such as myocardial infarction) are absent, patients presenting with both conditions present a unique challenge, particularly as the temporal relationship of each condition can often remain elusive from the clinical history. The question of whether the AF is driving, or significantly contributing to the left ventricular (LV) dysfunction, rather than merely a consequence of heart failure, has become ever more pertinent, especially as catheter ablation now offers a significant advancement over existing rhythm control strategies. This paper will review the inter-related physiological drivers of AF and heart failure before considering the implications from the outcomes of recent clinical trials in patients with AF and heart failure.

Mitogen-activated protein kinase p38 target regenerating islet-derived 3γ expression is upregulated in cardiac inflammatory response in the rat heart

Regenerating islet‐derived 3γ (Reg3γ) is a multifunctional protein, associated with various tissue injuries and inflammatory states. Since chronic inflammation is characteristics also for heart failure, the aim of this study was to characterize Reg3γ expression in cardiac inflammatory conditions. Reg3γ expression was studied in experimental rat models of myocardial infarction (MI) and pressure overload in vivo. For cell culture studies neonatal rat cardiac myocytes (NRCMs) were used. In addition, adenovirus‐mediated gene transfer of upstream mitogen‐activated protein kinase (MAPK) kinase 3b and p38α MAPK in vivo and in vitro was performed. Reg3γ mRNA (12.8‐fold, P < 0.01) and protein (5.8‐fold, P < 0.001) levels were upregulated during the postinfarction remodeling at day 1 after MI, and angiotensin II (Ang II) markedly increased Reg3γ mRNA levels from 6 h to 2 weeks. Immunohistochemistry revealed that the Ang II‐induced expression of Reg3γ was localized into the cardiac fibroblasts and myofibroblasts of the proliferating connective tissue in the heart. Stretching and treatments with endothelin‐1, lipopolysaccharide (LPS), and fibroblast growth factor‐1 increased Reg3γ mRNA levels in NRCMs. SB203580, a selective p38 MAPK inhibitor, markedly attenuated LPS and mechanical stretch‐induced upregulation of Reg3γ gene expression. Moreover, combined overexpression of MKK3bE and WT p38α increased Reg3γ gene expression in cultured cardiomyocytes in vitro and in the rat heart in vivo. Our study shows that cardiac stress activates Reg3γ expression and p38 MAPK is an upstream regulator of Reg3γ gene expression in heart. Altogether our data suggest Reg3γ is associated with cardiac inflammatory signaling.

Bone morphogenetic protein-2--a potential autocrine/paracrine factor in mediating the stretch activated B-type and atrial natriuretic peptide expression in cardiac myocytes

Hemodynamic overload exposes the heart to variety of neural, humoral and mechanical stresses. Even without the neurohumoral control of the entire organism cardiac myocytes have the ability to sense mechanical stretch and convert it into adaptive intracellular signals. This process is controlled by several growth factors. Here we show that mechanical stretch in vitro and hemodynamic overload in vivo activated the expression of bone morphogenetic protein-2 (BMP-2), while expression of BMP-4 was temporarily attenuated by stretch. BMP-2 and BMP-4 alone stimulated B-type and atrial natriuretic peptide (BNP and ANP) expression and protein synthesis, and activated transcription factor GATA-4 resembling the effects of mechanical stretch of cultured cardiac myocytes. Further, BMP antagonist Noggin was able to inhibit stretch and hypertrophic agonist induced BNP and ANP expression. Together these data provide evidence for BMP-2 as a new autocrine/paracrine factor that regulates cardiomyocyte mechanotransduction and adaptation to increased mechanical stretch.

Successful management of enzyme replacement therapy in related fabry disease patients with severe adverse events by switching from agalsidase Beta (fabrazyme(®)) to agalsidase alfa (replagal (®))

BACKGROUND

Enzyme replacement therapy (ERT) is the only approved therapy for Fabry disease. In June 2009, there was a worldwide shortage of agalsidase beta, necessitating dose reductions or switching to agalsidase alfa in some patients.

CASE PRESENTATION

We present two cases of Fabry disease (a parent and a child) who received agalsidase beta for 27 months at the licensed dose and 10 months at a reduced dose, followed by a switch to agalsidase alfa for 28 months. Case 1, a 26-year-old male had severe coughing and fatigue during ERT with agalsidase beta requiring antitussive and asthmatic drug therapy. After switching to agalsidase alfa, the coughing gradually resolved completely. Case 2, a 62-year-old female had advanced cardiac manifestations at the time of diagnosis. Despite receiving ERT with the approved dose of agalsidase beta, she experienced aggravation of congestive heart failure and was hospitalized. After switching to agalsidase alfa with standard care in heart disease, BNP level, echocardiographic parameters, eGFR rate and lyso-Gb3 levels were improved or stabilized.

CONCLUSIONS

We report on two Fabry disease patients who experienced severe adverse events while on approved and/or reduced doses of agalsidase beta. Switching to agalsidase alfa associated with standard care in heart disease led to resolution or improvement in the cardiorespiratory status. And reduction in dose associated with standard care in respiratory disease was useful for decrease in cough and fatigue. Plasma BNP level was useful for monitoring heart failure and the effects of ERT.

Endogenous endothelin 1 mediates angiotensin II-induced hypertrophy in electrically paced cardiac myocytes through EGFR transactivation, reactive oxygen species and NHE-1

Emerging evidence supports a key role for endothelin-1 (ET-1) and the transactivation of the epidermal growth factor receptor (EGFR) in angiotensin II (Ang II) action. We aim to determine the potential role played by endogenous ET-1, EGFR transactivation and redox-dependent sodium hydrogen exchanger-1 (NHE-1) activation in the hypertrophic response to Ang II of cardiac myocytes. Electrically paced adult cat cardiomyocytes were placed in culture and stimulated with 1 nmol l(-1) Ang II or 5 nmol l(-1) ET-1. Ang II increased ~45 % cell surface area (CSA) and ~37 % [(3)H]-phenylalanine incorporation, effects that were blocked not only by losartan (Los) but also by BQ123 (AT1 and ETA receptor antagonists, respectively). Moreover, Ang II significantly increased ET-1 messenger RNA (mRNA) expression. ET-1 similarly increased myocyte CSA and protein synthesis, actions prevented by the reactive oxygen species scavenger MPG or the NHE-1 inhibitor cariporide (carip). ET-1 increased the phosphorylation of the redox-sensitive ERK1/2-p90(RSK) kinases, main activators of the NHE-1. This effect was prevented by MPG and the antagonist of EGFR, AG1478. Ang II, ET-1 and EGF increased myocardial superoxide production (187 ± 9 %, 149 ± 8 % and 163.7 ± 6 % of control, respectively) and AG1478 inhibited these effects. Interestingly, Los inhibited only Ang II whilst BQ123 cancelled both Ang II and ET-1 actions, supporting the sequential and unidirectional activation of AT1, ETA and EGFR. Based on the present evidence, we propose that endogenous ET-1 mediates the hypertrophic response to Ang II by a mechanism that involves EGFR transactivation and redox-dependent activation of the ERK1/2-p90(RSK) and NHE-1 in adult cardiomyocytes.

NGAL and NT-proBNP levels in diabetic patients with macroproteinuria

BACKGROUND

In patients with heart failure plasma N-terminal pro-brain natriuretic peptide (NT-proBNP) levels are correlated to urine neutrophil gelatinase-associated lipocalin (NGAL) levels. We prospectively evaluated the relationship among glomerular filtration rate (eGFR), urine albumin-to-creatinine ratio (ACR), urine and serum NGAL and NT-proBNP levels in 20 type II diabetic patients with macroalbuminuria at 4-month intervals.

RESULTS

Compared with 20 age, gender-matched healthy controls, diabetic patients had higher urine and serum NGAL, serum NT-proBNP and lower eGFR. The eGFR of the patients at the baseline, the 4th and the 8th month were 29.6 ± 12.0, 27.8 ± 13.7 and 22.9 ± 10.4 mL/min/1.73 m(2), respectively. No significant change in urine NGAL levels was detected (p > 0.05), whereas there were significant increases in NT-proBNP, serum NGAL and urine ACR and significant decrease in eGFR as the study progressed (p < 0.05). Both the baseline and the 4th month urine ACR were positively correlated to NT-proBNP levels measured at the same periods (r: 0.451; p: 0.046; r: 0.489; p: 0.029 respectively). In all measurements, urine ACR was negatively correlated to serum albumin levels measured at the same periods (r: -0.792; p: 0.000; r: -0.716; p: 0.000; r: -0.531; p: 0.016 respectively). None of eGFR measurements was correlated with NT-proBNP (p > 0.05). Neither serum NGAL nor urinary NGAL levels are associated with NT-proBNP (p > 0.05).

CONCLUSION

Our findings show an association between NT-proBNP and proteinuria in type II diabetic patients with macroalbuminuria but not with serum and urine NGAL.

Regulation of cardiac melusin gene expression by hypertrophic stimuli in the rat

AIM

Melusin is an integrin β1-interacting protein proposed to act as a biomechanical sensor in the heart. We characterized mechanisms and signalling pathways regulating cardiac melusin expression.

METHODS

Infusion of arginine(8) -vasopressin (AVP) in Sprague-Dawley (SD) rats, spontaneously hypertensive rats (SHR) and double transgenic rats (dTGR) harbouring both human angiotensinogen and renin genes as well as infusion of angiotensin II (Ang II) in SD rats were used. The effect of direct left ventricular (LV) wall stretch was analysed by using isolated perfused rat heart preparation. For the cell culture studies, mouse atrial HL-1 cell line and neonatal rat ventricular myocytes (NRVMs) were used.

RESULTS

Left atrial melusin mRNA levels increased already after 30 min of AVP infusion. Ang II caused significant upregulation of left atrial melusin mRNA (2.1-fold at 6 h, P < 0.05) and protein (1.9-fold at 72 h, P < 0.05) levels. In contrast, LV melusin mRNA levels remained unchanged in response to both infusions, as well as to aortic banding-induced pressure overload. Direct LV wall stress or late-stage hypertensive heart disease did not modify LV melusin gene expression either. Interestingly, in atrial HL-1 cells, cyclic stretching increased melusin mRNA levels. Stretching and treatments with hypertrophic agonists increased melusin mRNA and protein levels in NRVMs, endothelin-1 being the most potent. PD98059, an extracellular signal-regulated protein kinase 1/2 inhibitor, markedly attenuated the endothelin-1-induced upregulation of melusin gene expression in NRVMs.

CONCLUSION

Multiple hypertrophic stimuli regulate melusin expression predominately in the atria, which may represent a necessary initial step in early adaptive remodelling processes.

The Anrep effect: 100 years later

Myocardial stretch elicits a rapid increase in developed force, which is mainly caused by an increase in myofilament calcium sensitivity (Frank-Starling mechanism). Over the ensuing 10-15 min, a second gradual increase in force takes place. This slow force response to stretch is known to be the result of an increase in the calcium transient amplitude and constitutes the in vitro equivalent of the Anrep effect described 100 years ago in the intact heart. In the present review, we will update and discuss what is known about the Anrep effect as the mechanical counterpart of autocrine/paracrine mechanisms involved in its genesis. The chain of events triggered by myocardial stretch comprises 1) release of angiotensin II, 2) release of endothelin, 3) activation of the mineralocorticoid receptor, 4) transactivation of the epidermal growth factor receptor, 5) increased formation of mitochondria reactive oxygen species, 6) activation of redox-sensitive kinases upstream myocardial Na(+)/H(+) exchanger (NHE1), 7) NHE1 activation, 8) increase in intracellular Na(+) concentration, and 9) increase in Ca(2+) transient amplitude through the Na(+)/Ca(2+) exchanger. We will present the experimental evidence supporting each of the signaling steps leading to the Anrep effect and its blunting by silencing NHE1 expression with a specific small hairpin interference RNA injected into the ventricular wall.

Mechanical stretch increases brain natriuretic peptide production and secretion in the human fetal membranes

Brain natriuretic peptide (BNP) is synthesized by human fetal membranes, both the amnion and chorion. This locally produced BNP inhibits the contraction of the human myometrium, contributing to the maintenance of myometrial quiescence during pregnancy. We tested the hypothesis that BNP production is increased by fetal membrane stretching, which is predicted to occur in the expanding uterus, and inhibited by epidermal growth factor (EGF), whose production in the fetal membranes increases in late pregnancy. Term fetal membranes were obtained during elective cesarean delivery before labor. Sections of membranes were placed in an isolated chamber containing DMEM: F12 medium (37°C) and stretched with a 35 g weight. Medium and tissue samples were collected at 0, 3, 6, 18, and 24 hours for measurement of messenger RNA (mRNA) and BNP levels in the presence/absence of EGF (2 × 10(-9 )mol/L). Inducible nitric oxide synthase (iNOS) and β-actin were also evaluated to discard a nonspecific effect of mechanical stretch on protein expression. We found that amnion and chorion stretching increased the BNP mRNA (reverse transcription-polymerase chain reaction [RT-PCR]) and protein (radioimmunosorbent assay [RIA]) levels from 18 hours onward. The effect of stretching was inhibited by EGF (2 × 10(-9) mol/L). Stretch did not increase iNOS or β-actin protein levels. We concluded that chorion and amnion stretching may increase BNP expression in the fetal membranes during pregnancy, while increasing biological activity of EGF may decrease BNP production in the chorion and amnion late in pregnancy. We postulate BNP is an important regulator of myometrial contractility during pregnancy, and its production is modulated by both stretch and progressive increase in EGF levels during pregnancy.

Mineralocorticoid receptor activation is crucial in the signalling pathway leading to the Anrep effect

The increase in myocardial reactive oxygen species after epidermal growth factor receptor transactivation is a crucial step in the autocrine/paracrine angiotensin II/endothelin receptor activation leading to the slow force response to stretch (SFR). Since experimental evidence suggests a link between angiotensin II or its AT1 receptor and the mineralocorticoid receptor (MR), and MR transactivates the epidermal growth factor receptor, we thought to determine whether MR activation participates in the SFR development in rat myocardium. We show here that MR activation is necessary to promote reactive oxygen species formation by a physiological concentration of angiotensin II (1 nmol l(-1)), since an increase in superoxide anion formation of ~50% of basal was suppressed by blocking MR with spironolactone or eplerenone. This effect was also suppressed by blocking AT1, endothelin (type A) or epidermal growth factor receptors, by inhibiting NADPH oxydase or by targeting mitochondria, and was unaffected by glucocorticoid receptor inhibition. All interventions except AT1 receptor blockade blunted the increase in superoxide anion promoted by an equipotent dose of endothelin-1 (1 nmol l(-1)) confirming that endothelin receptors activation is downstream of AT1. Similarly, an increase in superoxide anion promoted by an equipotent dose of aldosterone (10 nmol l(-1)) was blocked by spironolactone or eplerenone, by preventing epidermal growth factor receptor transactivation, but not by inhibiting glucocorticoid receptors or protein synthesis, suggesting non-genomic MR effects. Combination of aldosterone plus endothelin-1 did not increase superoxide anion formation more than each agonist separately. We found that aldosterone increased phosphorylation of the redox-sensitive kinases ERK1/2-p90RSK and the NHE-1, effects that were eliminated by eplerenone or by preventing epidermal growth factor receptor transactivation. Finally, we provide evidence that the SFR is suppressed by MR blockade, by preventing epidermal growth factor receptor transactivation or by scavenging reactive oxygen species, but it is unaffected by glucocorticoid receptor blockade or protein synthesis inhibition. Our results suggest that MR activation is a necessary step in the stretch-triggered reactive oxygen species-mediated activation of redox-sensitive kinases upstream NHE-1.

Resting and dobutamine stress test induced serum concentrations of brain natriuretic peptide in German Shepherd dogs

Studies of clinical uses of brain natriuretic peptide (BNP) represent one of the most important advances in cardiology since the introduction of echocardiography as a clinical diagnostic procedure. Defining the clinical potential of BNP in canine cardiology has not been completed yet. The aim of this study is to measure BNP concentrations in healthy German Shepherd dogs of different ages as a baseline in resting and when conventional protocol of the dobutamine stress test (DST) is applied to dogs. Concentrations of BNP were measured in blood serum by the radioimmunoassay method. The values of BNP concentrations were compared to cardiac parameters obtained by standard cardiac diagnostic procedures (radiology, electrocardiography and echocardiography). No significant differences in serum BNP concentrations existed in dogs of different ages. A statistically significant increase in BNP concentrations was registered after DST. These changes in BNP concentrations were related to ST/T electrocardiographic changes, and correlated to changes in the left ventricular internal diameter in systole (LVESD). These data suggest that BNP is not increased in aged dogs with normal cardiac systolic function and renal function, and that myocardial ischemia leads to a significant increase in BNP concentrations even in dogs with normal left ventricular function.

Mechanisms of atrial structural changes caused by stretch occurring before and during early atrial fibrillation

Structural remodelling occurring before, due to the underlying heart disease, and during atrial fibrillation (AF) sets the stage for permanent AF. Current therapy in AF aims to maintain sinus rhythm in symptomatic patients, but outcome is unfortunately poor. Stretch of the atria is a main contributor to atrial remodelling. In this review, we describe different aspects of structural remodelling as seen in animal models and in patients with AF, including atrial enlargement, cellular hypertrophy, dedifferentiation, fibrosis, apoptosis, and loss of contractile elements. In the second part, we describe downstream signals of mechanical stretch and their contribution to AF and structural remodelling. Ultimately, knowledge of mechanisms underlying structural remodelling may help to identify new pharmacological targets for AF prevention.

Endothelin signalling regulates volume-sensitive Cl- current via NADPH oxidase and mitochondrial reactive oxygen species

AIMS

We assessed regulation of volume-sensitive Cl(-) current (I(Cl,swell)) by endothelin-1 (ET-1) and characterized the signalling pathway responsible for its activation in rabbit atrial and ventricular myocytes.

METHODS AND RESULTS

ET-1 elicited I(Cl,swell) under isosmotic conditions. Outwardly rectified Cl(-) current was blocked by the I(Cl,swell)-selective inhibitor DCPIB or osmotic shrinkage and involved ET(A) but not ET(B) receptors. ET-1-induced current was abolished by inhibiting epidermal growth factor receptor (EGFR) kinase or phosphoinositide-3-kinase (PI-3K), indicating that these kinases were downstream. Regarding upstream events, activation of I(Cl,swell) by osmotic swelling or angiotensin II (AngII) was suppressed by ET(A) blockade, whereas AngII AT(1) receptor blockade failed to alter ET-1-induced current. Reactive oxygen species (ROS) produced by NADPH oxidase (NOX) stimulate I(Cl,swell). As expected, blockade of NOX suppressed ET-1-induced I(Cl,swell), but blockade of mitochondrial ROS production with rotenone also suppressed I(Cl,swell). I(Cl,swell) was activated by augmenting complex III ROS production with antimycin A or diazoxide; in this case, I(Cl,swell) was insensitive to NOX inhibitors, indicating that mitochondria were downstream from NOX. ROS generation in HL-1 cardiomyocytes measured by flow cytometry confirmed the electrophysiological findings. ET-1-induced ROS production was inhibited by blocking either NOX or mitochondrial complex I, whereas complex III-induced ROS production was insensitive to NOX blockade.

CONCLUSION

ET-1-ET(A) signalling activated I(Cl,swell) via EGFR kinase, PI-3K, and NOX ROS production, which triggered mitochondrial ROS production. ET(A) receptors were downstream effectors when I(Cl,swell) was elicited by osmotic swelling or AngII. These data suggest that ET-1-induced ROS-dependent I(Cl,swell) is likely to participate in multiple physiological and pathophysiological processes.

Inhibition of farnesylpyrophosphate synthase prevents angiotensin II-induced hypertrophic responses in rat neonatal cardiomyocytes: involvement of the RhoA/Rho kinase pathway

The RhoA/Rho-kinase (ROCK) pathway is involved in angiotensin (Ang) II-induced cardiac hypertrophy. However, it is still unclear whether inhibition of farnesylpyrophosphate (FPP) synthase can attenuate Ang II-induced hypertrophic responses, and whether it involves the RhoA/ROCK pathway. The anti-hypertrophic effects of inhibition of FPP synthase with alendronate in Ang II-cultured neonatal cardiomyocytes were partially reversed by geranylgeranyol (GGOH) and were mimicked by GGTI-286, a geranylgeranyl transferase-I inhibitor, C3 exoenzyme, an inhibitor of Rho, or Y-27632, an inhibitor of ROCK. Pull-down assay showed alendronate reduced-active RhoA by Ang II was also partially antagonized by GGOH. This study revealed that the inhibition of FPP synthase by alendronate reduces RhoA activation by diminishing geranylgeranylation which prevents Ang II-induced hypertrophic responses in neonatal cardiomyocytes.

ProBNP‐derived peptides in cardiac disease

The natriuretic peptides constitute a family of structurally related peptides that regulate fluid homeostasis, vascular tonus and growth. After the discovery of an endocrine component of the heart almost 25 years ago, the cardiac natriuretic peptides have now been fully accepted as useful markers in diverse aspects of cardiology including as diagnostic, therapeutic and prognostic markers of cardiac disease. In humans, atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) are mainly synthesized and secreted by the failing heart, whereas the related C-type natriuretic peptide (CNP) appears to be a local regulatory peptide secreted by the vascular endothelium. Accordingly, CNP is not a cardiac peptide. With the recent implementation of sensitive and specific immunoassays, increased plasma concentrations of proBNP-derived peptides have now been associated with several cardiac conditions, where the major application today seems related to ventricular dysfunction. Recently, focus has also turned to ischemic heart disease, since myocardial hypoxia increases the local BNP gene expression. This review recapitulates the established clinical applications of measuring proBNP-derived peptides in plasma. Furthermore, the evidence of increased cardiac BNP expression in ischemic heart disease will be emphasized. In turn, plasma measurement of proBNP-derived peptides may still hold new possibilities in screening for coronary artery disease.

Patterns of muscular strain in the embryonic heart wall

The hypothesis that inner layers of contracting muscular tubes undergo greater strain than concentric outer layers was tested by numerical modeling and by confocal microscopy of strain within the wall of the early chick heart. We modeled the looped heart as a thin muscular shell surrounding an inner layer of sponge-like trabeculae by two methods: calculation within a two-dimensional three-variable lumped model and simulated expansion of a three-dimensional, four-layer mesh of finite elements. Analysis of both models, and correlative microscopy of chamber dimensions, sarcomere spacing, and membrane leaks, indicate a gradient of strain decreasing across the wall from highest strain along inner layers. Prediction of wall thickening during expansion was confirmed by ultrasonography of beating hearts. Degree of stretch determined by radial position may thus contribute to observed patterns of regional myocardial conditioning and slowed proliferation, as well as to the morphogenesis of ventricular trabeculae and conduction fascicles. Developmental Dynamics 238:1535-1546, 2009. (c) 2009 Wiley-Liss, Inc.

Transient increase in plasma brain (B-type) natriuretic peptide after percutaneous transluminal coronary angioplasty

BACKGROUND

Brain (B-type) natriuretic peptide (BNP) is known to be secreted predominantly from the myocardium. Brain natriuretic peptide plasma concentrations have been shown to be markedly increased in patients with acute myocardial infarction; however, plasma BNP response during episodes of myocardial ischemia has not been established.

HYPOTHESIS

This study was designed to examine plasma BNP in patients with transient myocardial ischemia induced by inflation of a percutaneous transluminal coronary angioplasty (PTCA) balloon.

METHODS

Thirty consecutive patients (26 men and 4 women; mean age 61 years) who underwent PTCA, and another 49 patients (39 men and 10 women; mean age 63 years) who underwent diagnostic coronary angiography were enrolled in this study. Serum BNP concentrations were assayed in all patients.

RESULTS

Plasma BNP was increased significantly with a peak concentration of 66.1 +/- 65.2 pg/ml 24 h after PTCA. Coronary angiography did not cause plasma BNP increase (immediately before 30.4 +/- 29.0 pg/ml, 24 h after 33.7 +/- 30.6 pg/ml). No significant differences were present in hemodynamic parameters measured immediately before and 24 h after PTCA.

CONCLUSION

Plasma BNP is increased by transient myocardial ischemia induced by PTCA.

Regulation of ACE2 in cardiac myocytes and fibroblasts

Angiotensin-converting enzyme 2 (ACE2) preferentially forms angiotensin-(1-7) [ANG-(1-7)] from ANG II. We showed that cardiac ACE2 is elevated following treatment of coronary artery-ligated rats with AT1 receptor blockers (ARBs). Cardiac myocytes and fibroblasts were isolated from neonatal rats to determine the molecular mechanisms for the ACE2 upregulation by ARB treatment. ANG II significantly reduced ACE2 activity and downregulated ACE2 mRNA in cardiac myocytes, effects blocked by the ARB losartan, indicating that ANG II regulates ACE2. ANG II also reduced ACE2 mRNA in cardiac fibroblasts; however, no enzyme activity was detected, reflecting the limited expression of ACE2 in these cells. Endothelin-1 (ET-1) also significantly reduced myocyte ACE2 mRNA. The reduction in ACE2 mRNA by ANG II or ET-1 was blocked by inhibitors of mitogen-activated protein kinase kinase 1, suggesting that ANG II or ET-1 activates extracellular signal-regulated kinase (ERK) 1/ERK2 to reduce ACE2. Although ACE2 mRNA was not affected by ANG-(1-7), both the ANG II- and ET-1-mediated reductions in ACE2 mRNA were blocked by the heptapeptide. The ANG-(1-7) modulatory effect was prevented by the ANG-(1-7) receptor antagonist [D-Ala7]-ANG-(1-7), indicating that the ANG-(1-7) response was mediated by a specific AT(1-7) receptor. Myocyte treatment with atrial natriuretic peptide (ANP) also reversed the ACE2 mRNA downregulation by ANG II or ET-1, whereas treatment with ANP alone was ineffective. These results indicate that multiple hypertrophic and anti-hypertropic peptides regulate ACE2 production in myocytes, suggesting that ACE2 expression in the heart is dependent upon the compliment and concentration of regulatory molecules.

Brain natriuretic peptide is a good predictor for outcome in cardiac surgery

BACKGROUND AND AIM

The heart secretes brain natriuretic peptide (BNP) in response to myocardial stretch. The aim of this study was to determine whether adverse effects after cardiac surgery were associated with higher serum BNP levels pre-operatively.

METHODS

One hundred and thirty-five patients undergoing various cardiac procedures were included in the study, and N-terminal pro-BNP (NT-pro-BNP) was measured pre-operatively. Post-operative complications were defined as follows: (i) a post-operative length of stay in the intensive care unit (ICU) exceeding 48 h; (ii) mortality at 28 days; (iii) the need for inotropic agents and/or intra-aortic balloon pump (IABP); and (iv) renal failure. Serum NT-pro-BNP values were compared for patients with and without complications. The serum NT-pro-BNP level was also correlated with the euroSCORE and ejection fraction (EF).

RESULTS

Pre-operative serum NT-pro-BNP levels were significantly higher in patients with an ICU length of stay of more than 2 days or death prior to post-operative day 28 (3118 ng/l vs. 705 ng/l; P < 0.001). Pre-operative serum NT-pro-BNP levels were also significantly higher in patients needing inotropic agents (2628 ng/l vs. 548 ng/l; P < 0.001) or IABP insertion (3705 ng/l vs. 935 ng/l; P = 0.001) or developing renal failure (2857 ng/l vs. 945 ng/l; P < 0.001) post-operatively. The correlation between the serum NT-pro-BNP level and euroSCORE was good (r = 0.658; P < 0.001). The receiver operating characteristic (ROC) curves were used to assess the ability of serum NT-pro-BNP, euroSCORE and EF to predict outcome after cardiac surgery. This revealed an area under the ROC curve for the length of stay in the ICU or mortality at 28 days of 0.829 for serum NT-pro-BNP, 0.814 for euroSCORE and 0.328 for EF assessed by transesophageal echocardiography, indicating that the pre-operative serum NT-pro-BNP level is a good prognostic indicator for outcome after cardiac surgery.

CONCLUSION

Serum NT-pro-BNP is a good predictor for complications after cardiac surgery, and is as good as euroSCORE and better than EF.

Interpretation of B-type natriuretic peptide in cardiac disease and other comorbid conditions

B-Type natriuretic peptide (BNP) is elevated in states of increased ventricular wall stress. BNP is most commonly used to rule out congestive heart failure (CHF) in dyspneic patients. BNP levels are influenced by age, gender and, to a surprisingly large extent, by body mass index (BMI). In addition, it can be elevated in a wide variety of clinical settings with or without CHF. BNP is elevated in other cardiac disease states such as the acute coronary syndromes, diastolic dysfunction, atrial fibrillation (AF), amyloidosis, restrictive cardiomyopathy (RCM), and valvular heart disease. BNP is elevated in non-cardiac diseases such as pulmonary hypertension, chronic obstructive pulmonary disease, pulmonary embolism, and renal failure. BNP is also elevated in the setting of critical illness such as in acute decompensated CHF (ADHF) and sepsis. This variation across clinical settings has significant implications given the increasing frequency with which BNP testing is being performed. It is important for clinicians to understand how to appropriately interpret BNP in light of the comorbidities of individual patients to maximize its clinical utility. We will review the molecular biology and physiology of natriuretic peptides as well as the relevant literature on the utilization of BNP in CHF as well as in other important clinical situations, conditions that are commonly associated with CHF and or dyspnea.

Endothelin-1 and angiotensin II contribute to BNP but not c-fos gene expression response to elevated load in isolated mice hearts

The early events in the cardiac hypertrophic process induced by hemodynamic load include activation of B-type natriuretic peptide (BNP) and c-fos gene expression. However, it is unknown whether stretch acts directly or through local paracrine factors to trigger changes in cardiac gene expression. Herein we studied the involvement of endothelin-1 (ET-1) and angiotensin II (Ang II) in load-induced activation of left ventricular BNP and c-fos gene expression using an in vitro stretch model in isolated perfused adult mice hearts. Two-hour stretch induced by increasing coronary flow rate from 2 to 5 ml/min increased the expression of BNP and c-fos genes by 1.9- and 1.5-fold, respectively (P<0.001 and P<0.05). A mixed ET(A/B) receptor antagonist bosentan attenuated the BNP gene expression response to load by 58% (P<0.005). A similar 53% inhibition was observed with the selective ET(A) receptor blocker BQ-123 (P<0.05). Type 1 Ang II receptor antagonist CV-11974 decreased the activation of BNP gene expression by 50% (P<0.05). In contrast, the activation of c-fos gene expression was not inhibited by antagonists of ET(A/B) and AT(1) receptors. Our results show that ET-1 and Ang II play a key role in the induction of BNP, but not c-fos gene expression in response to load in intact adult murine hearts.

The positive inotropic effect of angiotensin II: role of endothelin-1 and reactive oxygen species

Many effects believed to be because of angiotensin II (Ang II) are attributable to the action of endothelin (ET)-1, which is released/produced by Ang II. We investigated whether Ang II elicits its positive inotropic effect (PIE) by the action of endogenous ET-1, in addition to the role played by reactive oxygen species (ROS) in this mechanism. Cat cardiomyocytes were used for: (1) sarcomere shortening measurements; (2) ROS measurements by epifluorescence; (3) immunohistochemical staining for preproET-1, BigET-1, and ET-1; and (4) measurement of preproET-1 mRNA by RT-PCR. Cells were exposed to 1 nmol/L Ang II for 15 minutes. This low concentration of Ang II increases sarcomere shortening by 29.2+/-3.7% (P<0.05). This PIE was abrogated by Na+/H+ exchanger or Na+/Ca2+ exchanger reverse mode inhibition. The production of ROS increased in response to Ang II treatment (DeltaROS respect to control: 68+/-15 fluorescence units; P<0.05). The Ang II-induced PIE and ROS production were blocked by the Ang II type 1 receptor blocker losartan, the nonselective ET-1 receptor blocker TAK044, the selective ETA receptor blocker BQ-123, or the ROS scavenger N-(2-mercapto-propionyl)glycine. Exogenous ET-1 (0.4 nmol/L) induced a similar PIE and increase in ROS production to those caused by Ang II. Immunostaining for preproET-1, BigET-1, and ET-1 was positive in cardiomyocytes. The preproET-1 mRNA abundance increased from 100+/-4.6% in control to 241.9+/-39.9% in Ang II-treated cells (P<0.05). We conclude that the PIE after exposure to 1 nmol/L Ang II is due to endogenous ET-1 acting through the ETA receptor and triggering ROS production, Na+/H+ exchanger stimulation, and Na+/Ca2+ exchanger reverse mode activation.

Inverse regulation of preproendothelin-1 and endothelin-converting enzyme-1beta genes in cardiac cells by mechanical load

Mechanical stretch and para- and/or autocrine factors, including endothelin-1, induce hypertrophy of cardiac myocytes and proliferation of fibroblasts. To investigate the effect of mechanical load on endothelin-1 production and endothelin system gene expression in neonatal rat ventricular myocytes and fibroblasts, we exposed cells to cyclic mechanical stretch in vitro (0.5 Hz, 10-25% elongation, from 1 min to 24 h). Endothelin-1 peptide levels were measured from culture media of myocytes and fibroblasts and human umbilical vein endothelial cells (positive control) by specific radioimmunoassay. Preproendothelin-1 promoter activity was measured via transfection of reporter plasmids and mRNA levels with Northern blot analysis or quantitative RT-PCR. Activity of extracellular signal-regulated kinase was quantified with specific kinase assay. We found that stretching of myocytes activated preproendothelin-1 gene expression, including promoter activation, transient mRNA level increases, and augmented endothelin-1 secretion. In contrast, preproendothelin-1 gene expression was inhibited in stretched fibroblasts. Endothelin-converting enzyme-1beta mRNA levels elevated in stretched fibroblasts but decreased in stretched myocytes. Endothelin receptor type A mRNA levels declined in stretched myocytes, whereas levels were below detection in fibroblasts. Stretch activated extracellular signal-regulated kinase in myocytes, and when the kinase activity was pharmacologically inhibited, the preproendothelin-1 induction was suppressed. Transient overexpression of mitogen-activated ERK-activating kinase-1 induced preproendothelin-1 promoter in myocytes. In summary, mechanical stretch distinctly regulates endothelin system gene expression in cardiac myocytes and fibroblasts. The inhibition of the endothelin system may affect cardiac mechanotransduction and therefore provides an approach in treatment of load-induced cardiac pathology.

Vascular and renal actions of brain natriuretic peptide in man: physiology and pharmacology

During the last decade brain natriuretic peptide (BNP) has received increasing attention as a potential marker of cardiovascular disease. BNP may act as a compensating mechanism in cardiovascular diseases in order to reduce preload. However, the increase in endogenous BNP is often not sufficient to compensate for volume overload in diseases like established hypertension and heart failure. The reported hemodynamic and renal effects of BNP in man differ largely between studies, because of differences in design and doses of BNP employed. In the pharmacological range, BNP has clear blood pressure and afterload lowering effects, and in the kidney blood flow and filtration is increased with concomitant natriuresis and diuresis. While in the physiological range BNP does not affect blood pressure and reduces preload only, and induces natriuresis/diuresis without changes in renal blood flow and filtration. There is increasing evidence from vascular studies that BNP preferentially acts on the venous system resulting in preload reduction, in contrast to atrial natriuretic peptide which acts preferentially on the arterial system to reduce afterload. This review summarizes our current understanding of BNP, and discuss its regulation and mechanisms of action on the vasculature and the kidneys.

Molecular regulation of the brain natriuretic peptide gene

After brain natriuretic peptide (BNP) was isolated in 1988, rapid progress was made in cloning its cDNA and gene, facilitating studies of tissue-specific expression and molecular regulation of gene expression. This review focuses on the molecular determinants of regulation of the rat and human BNP genes, including signaling pathways that impact on changes in gene expression and cis regulatory elements responsive to these signaling pathways. For both rat and human genes, elements in the proximal promoter (-124 to -80), including GATA, MCAT, and AP-1-like, have been shown to contribute to basal and inducible regulation. More distal elements in the human BNP gene respond to calcium signals (an NF-AT site at -927), thyroid hormone (a thyroid-responsive element at -1000), and mechanical stretch (shear stress-responsive elements at -652 and -162). Understanding how BNP is regulated by signaling molecules that are activated in the hypertrophied and ischemic heart should be useful in understanding the underlying pathology. This may lead to therapeutic strategies that prevent hypertrophy while allowing for the beneficial effects of BNP production.

Intracellular signaling following myocardial stretch: an autocrine/paracrine loop

The stretch of adult papillary muscle elicits a chain of autocrine/paracrine events in which the Na(+)/H(+) exchanger (NHE-1) activation is the central step. This activation is induced by a sequential angiotensin II-endothelin (Ang II-ET) release and results in an increase in intracellular Na(+) (Na(+)(i)) without significant changes in intracellular pH. The increase in Na(+)(i) negatively shifts the reverse potential of the Na(+)/Ca(2+) exchanger (NCX) thus inducing cell Ca(2+) influx that augments myocardial contractility. This increase in force represents the mechanical counterpart of the autocrine/paracrine mechanism triggered by stretch and has been called the slow force response (SFR) to stretch.

Determinants of inducible brain natriuretic peptide promoter activity

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

Paradoxical changes in brain natriuretic peptide levels and loading conditions after intravenous conscious sedation

BACKGROUND

Elevated filling pressure and wall stress have been proposed as stimuli for elevated brain natriuretic peptide (BNP) levels. Narcotic and benzodiazepine sedation, such as is used for transesophageal echocardiography (TEE), is known to decrease filling pressures. We hypothesized that lower filling pressure and wall stress associated with intravenous conscious sedation (IVCS) would lead to lower BNP levels.

METHODS

We studied BNP levels, blood pressure, and echocardiographic indices of filling pressure and wall stress before and after IVCS and TEE.

RESULTS

When data before and after IVCS and TEE were compared, mean blood pressure decreased (149 +/- 24/83 +/- 14 mm Hg vs 126 +/- 29/69 +/- 14; P < .01), as did mitral Doppler E wave velocity (82 +/- 23 cm/s vs 76 +/- 22; P < .05), right ventricular/atrial gradient (31 +/- 10 mm Hg vs 29 +/- 13; P < .05), and wall stress. However, BNP levels increased (195 +/- 407 pg/mL vs 238 +/- 458; P < .01).

CONCLUSIONS

In a series of patients undergoing clinically indicated TEE, BNP levels increase above baseline after IVCS. The increase in BNP occurs despite lower blood pressure, lower mitral Doppler E velocity, lower right ventricular/atrial gradient, and lower wall stress compared with baseline. The mechanism of the paradoxical increase in BNP is not entirely clear, but it may conceivably be a result of counterregulatory hormone release caused by acute decrease in blood pressure.

Acute myocardial hypoxia increases BNP gene expression

It is well established that cardiac failure increases cardiac B-type natriuretic peptide (BNP) expression due to myocardial stretching. However, patients with ischemic heart disease also display increased plasma BNP and proBNP concentrations despite preserved cardiac function. In this study, we examined whether acute myocardial hypoxia increases cardiac BNP expression. Surgical reduction of the blood flow to an area of the anterior ventricular wall in pigs reduced the myocardial oxygen tension from 46 +/- 4 to 13 +/- 5 mmHg. The tissue contents of VEGF and BNP mRNA increased 1.8-fold and 3.5-fold, respectively (n=10, P<0.005) in hypoxic compared with normoxic ventricular myocardium after 2.2 +/- 0.2 h; the magnitude of the increase in BNP mRNA expression was positively correlated with that of VEGF in hypoxic myocardium (r=0.66, P<0.05). In support of a hypoxia-induced increase of BNP gene transcription, the content of a premature BNP mRNA was increased in hypoxic myocardium (4.8-fold, P<0.005) and in freshly harvested ventricular myocytes when kept in culture flasks and oxygen-deprived for 3 h (2.2-fold, P=0.002). ProBNP peptide accumulated in the medium of freshly harvested ventricular myocyte cultures but was undetectable in ventricular myocardium, indicating rapid release of the newly synthesized proBNP peptide. Accordingly, the plasma proBNP concentration increased after 2 h of myocardial hypoxia (P=0.028). Cumulatively, the data suggest that acute hypoxia stimulates cardiac BNP expression.

Thioredoxin-interacting protein controls cardiac hypertrophy through regulation of thioredoxin activity

BACKGROUND

Although cellular redox balance plays an important role in mechanically induced cardiac hypertrophy, the mechanisms of regulation are incompletely defined. Because thioredoxin is a major intracellular antioxidant and can also regulate redox-dependent transcription, we explored the role of thioredoxin activity in mechanically overloaded cardiomyocytes in vitro and in vivo.

METHODS AND RESULTS

Overexpression of thioredoxin induced protein synthesis in cardiomyocytes (127+/-5% of controls, P<0.01). Overexpression of thioredoxin-interacting protein (Txnip), an endogenous thioredoxin inhibitor, reduced protein synthesis in response to mechanical strain (89+/-5% reduction, P<0.01), phenylephrine (80+/-3% reduction, P<0.01), or angiotensin II (80+/-4% reduction, P<0.01). In vivo, myocardial thioredoxin activity increased 3.5-fold compared with sham controls after transverse aortic constriction (P<0.01). Aortic constriction did not change thioredoxin expression but reduced Txnip expression by 40% (P<0.05). Gene transfer studies showed that cells that overexpress Txnip develop less hypertrophy after aortic constriction than control cells in the same animals (28.1+/-5.2% reduction versus noninfected cells, P<0.01).

CONCLUSIONS

Thus, even though thioredoxin is an antioxidant, activation of thioredoxin participates in the development of pressure-overload cardiac hypertrophy, demonstrating the dual function of thioredoxin as both an antioxidant and a signaling protein. These results also support the emerging concept that the thioredoxin inhibitor Txnip is a critical regulator of biomechanical signaling.

Role of the epidermal growth factor receptor in signaling strain-dependent activation of the brain natriuretic peptide gene

The epidermal growth factor receptor (EGFR) and ectoshedding of heparin-binding epidermal growth factor (HBEGF), an EGFR ligand, have been linked to the development of cardiac myocyte hypertrophy. However, the precise role that the liganded EGFR plays in the transcriptional activation of the gene program that accompanies hypertrophy remains undefined. Utilizing the human (h) BNP gene as a model of hypertrophy-dependent gene activation, we show that activation of the EGFR plays an important role in mediating mechanical strain-dependent stimulation of the hBNP promoter. Strain promotes endothelin (ET) generation through NAD(P)H oxidase-dependent production of reactive oxygen species. ET in turn induces metalloproteinase-mediated cleavage of pro-HBEGF and ectoshedding of HBEGF, which activates the EGFR and stimulates hBNP promoter activity. HBEGF also stimulates other phenotypic markers of hypertrophy including protein synthesis and sarcomeric assembly. The antioxidant N-acetylcysteine or the NAD(P)H oxidase inhibitor, apocynin, inhibited strain-dependent activation of the ET-1 promoter, HBEGF shedding, and hBNP promoter activation. The metalloproteinase inhibitor, GM-6001, prevented the induction of HBEGF ectoshedding and the hBNP promoter response to strain, suggesting a critical role for the metalloproteinase-dependent cleavage event in signaling the strain response. These findings suggest that metalloproteinase activity as an essential step in this pathway may prove to be a relevant therapeutic target in the management of cardiac hypertrophy.

Activation of gp130 transduces hypertrophic signal through interaction of scaffolding/docking protein Gab1 with tyrosine phosphatase SHP2 in cardiomyocytes

Grb2-associated binder-1 (Gab1) is a scaffolding/docking protein and contains a Pleckstrin homology domain and potential binding sites for Src homology (SH) 2 and SH3 domains. Gab1 is tyrosine phosphorylated and associates with protein tyrosine phosphatase SHP2 and p85 phosphatidylinositol 3-kinase on stimulation with various cytokines and growth factors, including interleukin-6. We previously demonstrated that interleukin-6-related cytokine, leukemia inhibitory factor (LIF), induced cardiac hypertrophy through gp130. In this study, we report the role of Gab1 in gp130-mediated cardiac hypertrophy. Stimulation with LIF induced tyrosine phosphorylation of Gab1, and phosphorylated Gab1 interacted with SHP2 and p85 in cultured cardiomyocytes. We constructed three kinds of adenovirus vectors, those carrying wild-type Gab1 (AdGab1WT), mutated Gab1 lacking SHP2 binding site (AdGab1F627/659), and beta-galactosidase (Adbeta-gal). Compared with cardiomyocytes infected with Adbeta-gal, longitudinal elongation of cardiomyocytes induced by LIF was enhanced in cardiomyocytes infected with AdGab1WT but inhibited in cardiomyocytes infected with AdGab1F627/659. Upregulation of BNP mRNA expression by LIF was evoked in cardiomyocytes infected with Adbeta-gal and AdGab1WT but not in cardiomyocytes infected with AdGab1F627/659. In contrast, Gab1 repressed skeletal alpha-actin mRNA expression through interaction with SHP2. Furthermore, activation of extracellular signal-regulated kinase 5 (ERK5) was enhanced in cardiomyocytes infected with AdGab1WT compared with cardiomyocytes infected with Adbeta-gal but repressed in cardiomyocytes infected with AdGab1F627/659. Coinfection of AdGab1WT with adenovirus vector carrying dominant-negative ERK5 abrogated longitudinal elongation of cardiomyocytes induced by LIF. Taken together, these findings indicate that Gab1-SHP2 interaction plays a crucial role in gp130-dependent longitudinal elongation of cardiomyoctes through activation of ERK5.

Dual role of endothelin-1 via ETA and ETB receptors in regulation of cardiac contractile function in mice

An increase in coronary perfusion pressure leads to increased cardiac contractility, a phenomenon known as the Gregg effect. Exogenous endothelin (ET)-1 exerts a positive inotropic effect; however, the role of endogenous ET-1 in the contractile response to elevated load is unknown. We characterized here the role of ETA and ETB receptors in regulation of contractility in isolated, perfused mouse hearts subjected to increased coronary flow. Elevation of coronary flow from 2 to 5 ml/min resulted in 80 +/- 10% increase in contractile force (P < 0.001). BQ-788 (ETB receptor antagonist) augmented the load-induced contractile response by 35% (P < 0.05), whereas bosentan (ETA/B receptor antagonist) and BQ-123 (ETA receptor antagonist) attenuated it by 34% and 56%, respectively (P < 0.05). CV-11974 (ANG II type 1 receptor antagonist) did not modify the increase in contractility. These results show that endogenous ET-1 is a key mediator of the Gregg effect in mouse hearts. Moreover, ET-1 has a dual role in the regulation of cardiac contractility: ETA receptor-mediated increase in contractile force is suppressed by ETB receptors.

GATA-4 is a nuclear mediator of mechanical stretch-activated hypertrophic program

In overloaded heart the cardiomyocytes adapt to increased mechanical and neurohumoral stress by activation of hypertrophic program, resulting in morphological changes of individual cells and specific changes in gene expression. Accumulating evidence suggests an important role for the zinc finger transcription factor GATA-4 in hypertrophic agonist-induced cardiac hypertrophy. However, its role in stretch-induced cardiomyocyte hypertrophy is not known. We employed an in vitro mechanical stretch model of cultured cardiomyocytes and used rat B-type natriuretic peptide promoter as stretch-sensitive reporter gene. Stretch transiently increased GATA-4 DNA binding activity and transcript levels, which was followed by increases in the expression of B-type natriuretic peptide as well as atrial natriuretic peptide and skeletal alpha-actin genes. The stretch inducibility mapped primarily to the proximal 520 bp of the B-type natriuretic peptide promoter. Mutational studies showed that the tandem GATA consensus sites of the proximal promoter in combination with an Nkx-2.5 binding element are critical for stretch-activated B-type natriuretic peptide transcription. Inhibition of GATA-4 protein production by adenovirus-mediated transfer of GATA-4 antisense cDNA blocked stretch-induced increases in B-type natriuretic peptide transcript levels and the sarcomere reorganization. The proportion of myocytes with assembled sarcomeres in control adenovirus-infected cultures increased from 14 to 59% in response to stretch, whereas the values for GATA-4 antisense-treated cells were 6 and 13%, respectively. These results show that activation of GATA-4, in cooperation with a factor binding on Nkx-2.5 binding element, is essential for mechanical stretch-induced cardiomyocyte hypertrophy.

Cardiac hormones as diagnostic tools in heart failure

In patients with heart failure, plasma levels of atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), and the N-terminal fragments of their prohormones (N-ANP and N-BNP) are elevated, because the cardiac hormonal system is activated by increased wall stretch due to increased volume and pressure overload. Patients suspected of having heart failure can be selected for further investigations on the basis of having an elevated plasma concentration of N-ANP, BNP, and N-BNP. High levels of cardiac hormones identify those at greatest risk for future serious cardiovascular events. Moreover, adjusting heart failure treatment to reduce plasma levels of N-BNP may improve outcome. Cardiac hormones are most useful clinically as a rule-out test. In acutely symptomatic patients, a very high negative predictive value is coupled with a relatively high positive predictive value. Measurement of cardiac hormones in patients with heart failure may reduce the need for hospitalizations and for more expensive investigations such as echocardiography. However, there have also been conflicting reports on the diagnostic value of cardiac hormones, they are not specific for any disease, and the magnitude of the effects of age and gender on BNP in the normal subgroup suggests that these parameters need to be considered when interpreting cardiac hormone levels.

Triiodothyronine increases brain natriuretic peptide (BNP) gene transcription and amplifies endothelin-dependent BNP gene transcription and hypertrophy in neonatal rat ventricular myocytes

Brain natriuretic peptide (BNP) gene expression is a well documented marker of hypertrophy in the cardiac myocyte. Triiodothyronine (T(3)), the bioactive form of thyroid hormone, triggers a unique form of hypertrophy in cardiac myocytes that accompanies the selective activation or suppression of specific gene targets. In this study, we show that the BNP gene is a target of T(3) action. BNP secretion was increased 6-fold, BNP mRNA levels 3-fold, and BNP promoter activity 3-5-fold following T(3) treatment. This was accompanied by an increase in myocyte size, sarcomeric organization, and protein synthesis. Of note, several of the responses to T(3) synergized with those to the conventional hypertrophic agonist endothelin. The response to the liganded thyroid hormone receptor (TR) was mediated by an unusual thyroid hormone response element located between -1000 and -987 relative to the transcription start site. Both TR homodimers and TR.retinoid X receptor heterodimers associated with this element in an electrophoretic mobility shift assay. Protein fragments harboring the LXXLL motifs of the coactivators GRIP1 and SRC1 or TRAP220 interacted predominantly with the TR.retinoid X receptor heterodimeric pair in a ligand-dependent fashion. Both TR homodimers and heterodimers in the unliganded state selectively associated with glutathione S-transferase-nuclear receptor corepressor fragments harboring one of three receptor interaction domains containing the sequence (I/L)XX(I/V)I. These interactions were dissociated following the addition of T(3). Collectively, these findings identify the BNP gene as a potential model for the investigation of TR-dependent gene regulation in the heart.

Brain natriuretic peptide concentration in dogs with heart disease and congestive heart failure

Plasma brain natriuretic peptide concentration ([BNP]) is high in humans with cardiac disease and is further increased with congestive heart failure (CHF). The hypotheses of this study were that dogs with moderate to severe mitral regurgitation due to myxomatous mitral valve disease (MVD) would have increased plasma [BNP] compared to normal dogs, that plasma [BNP] would be higher in dogs with CHP, and that plasma [BNP] would predict premature death from cardiovascular disease. The study population consisted of 34 dogs: 9 normal dogs and 25 dogs with MVD. Patients were divided into 4 groups: group 1-10 dogs with moderate to severe MVD and no radiographic evidence of CHF; group II--6 dogs with severe MVD and mild CHF; group III--7 dogs with severe MVD and moderate CHF; and group IV--2 dogs with severe MVD and severe CHF. Diagnostic tests included thoracic radiographs, an echocardiogram, a serum chemistry profile, and the measurement of plasma [BNP] by a canine-specific radioimmunoassay. There was a significant positive correlation between the plasma [BNP] and heart disease/failure groups (P = .0036). Plasma [BNP] increased with progressively increasing severity of MVD and CHE Group I dogs had higher plasma [BNP] than did control dogs (P < .0001), and plasma [BNP] was higher in dogs with CHF (groups II-IV versus group I; P = .012). Plasma [BNP] was also weakly positively correlated with left atrial size (r = 0.43, P = .04). For every 10-pg/mL increase in plasma [BNP], the mortality rate over 4 months' time increased approximately 44%.

Chamber-dependent expression of brain natriuretic peptide and its mRNA in normal and diabetic pig heart

Brain natriuretic peptide (BNP) is produced in cardiac myocytes, and increased secretion is closely associated with cardiac dysfunction. However, several fundamental aspects of BNP expression in the myocardium have not yet been resolved. In the present study, we report the presence of a precursor BNP mRNA transcript and a mature BNP mRNA transcript in normal porcine hearts. In normal pigs, the amount of precursor BNP mRNA was similar in atrial and ventricular myocardium, whereas the mature BNP transcript was 10- to 50-fold more abundant in atrial than in ventricular myocardium. Quantitation of proBNP in normal porcine hearts by radioimmunoassay disclosed abundant proBNP in the atria, whereas proBNP was undetectable in the ventricles. Laser confocal microscopy revealed proBNP in secretory granules of atrial but not in the ventricular myocardium of normal pigs. Mild streptozotocin-induced diabetes doubled the expression of BNP mRNA in porcine atrial myocardium (P=0.03), but was without effect on BNP mRNA in the ventricular myocardium. The data suggest that BNP mRNA processing and proBNP storage differ between the atrial and ventricular myocardium. The results also imply that diabetes increases cardiac BNP expression in a chamber-dependent manner.