Safety and bioactivity of intracoronary delivery of naked plasmid DNA encoding human atrial natriuretic factor

AIM

To evaluate the safety and bioactivity of catheter-mediated intracoronary gene delivery of naked plasmid DNA encoding human atrial natriuretic factor (hANF).

METHODS

hANF gene delivery was performed in 12 canines. For each canine, 4 mg of reconstructed naked plasmid DNA encoding hANF (pCR3*hANF, n=6) or pCR3 (n=6, control) in 2 mL normal saline was injected into left coronary artery via a coronary angiographic catheter. The expression of hANF mRNA in left ventricular myocardium, liver, lung, and kidney was identified by reverse transcription polymerase chain reaction and Southern blot analysis 40 d after gene delivery. Plasma ANF levels were determined by radioimmunoassay.

RESULTS

The naked pCR3*hANF caused significant expression of hANF mRNA in ventricular myocardium (P <0.01). No hANF mRNA was detected in distal tissues, including liver, lung, and kidney (P >0.05). ANF levels were significantly higher in pCR3*hANF group than those in control group.

CONCLUSION

These facts firstly demonstrate that intracoronary delivery of naked pCR3*hANF is probably a safe and feasible method for gene delivery by which hANF gene can be expressed in ventricular myocardium effectively.

Intrauterine growth restriction in rats is associated with hypertension and renal dysfunction in adulthood

Epidemiological studies have produced evidence that unfavorable intrauterine environments during fetal life may lead to adverse outcomes in adulthood. We have previously shown that a low-sodium diet, given to pregnant rats over the last week of gestation, results in intrauterine growth restriction (IUGR). We hypothesize that pups born with IUGR are more susceptible to the development of hypertension in adulthood. IUGR fetuses and rats aged 1 wk were characterized for organ growth and renal morphogenesis. The adults (12 wk) were evaluated for weight, systolic blood pressure, activity of the renin-angiotensin-aldosterone system (RAAS), and renal function; hearts and kidneys underwent a histological examination. Brain and cardiac ventricle-to-body ratios were increased in IUGR fetuses compared with age-matched controls, whereas the kidney-to-body ratio was unchanged. Systolic blood pressure was elevated in both IUGR male and female adults. Plasma aldosterone levels were not correlated with increased plasma renin activity. Moreover, urinary sodium was decreased, whereas plasma urea was elevated in both males and females, and creatinine levels were augmented only in females, suggesting a glomerular filtration impairment in IUGR. In our model of IUGR induced by a low-sodium diet given to pregnant rats, high blood pressure, alteration of the RAAS, and renal dysfunction are observed in adult life. Differences observed between male and female adults suggest the importance of gender in outcomes in adulthood after IUGR.

Longstanding atrial fibrillation causes depletion of atrial natriuretic peptide in patients with advanced congestive heart failure

BACKGROUND

Congestive heart failure (CHF) is characterized by neurohormonal activation, including increased plasma concentrations of atrial natriuretic peptide (ANP) and N-terminal ANP (N-ANP). Onset of atrial fibrillation (AF) further increases these peptides, but it may be hypothesized that concentrations decrease during longstanding AF due to inherent atrial degeneration.

AIM

We sought to investigate the relation between neurohormonal activation in patients with CHF and the duration of concomitant AF.

METHODS

The study group comprised 60 patients (age 70 +/- 8 years) with advanced CHF due to left ventricular systolic dysfunction (left ventricular ejection fraction (LVEF) < 0.35) and chronic AF (duration 21 (1-340) months). Plasma neurohormone concentrations were measured, and multiple regression analysis was performed to identify their clinical predictors.

RESULTS

Median plasma neurohormone concentrations were: ANP 113 pmol/l, N-ANP 1187 pmol/l, norepinephrine 496 pg/ml, renin 127 micro units/l, aldosterone 128 pg/ml and endothelin 8.1 pg/ml. Norepinephrine, renin, aldosterone and endothelin were not significantly related to the duration of AF. In contrast, ANP decreased along with the duration of AF (P = 0.03), while the same trend was observed for N-ANP (P = 0.10). However, for these peptides a first order interaction with LVEF was present, which was not observed in the other neurohormones. In patients with LVEF > 0.25 ANP and N-ANP increased along with the duration of AF, whereas in patients with LVEF < or = 0.25 an inverse relation between ANP (P = 0.02) and N-ANP (P = 0.04) and the duration of AF was present, longer-standing AF being associated with lower concentrations.

CONCLUSION

In patients with advanced CHF with low LVEF plasma ANP and N-ANP concentrations decrease during longstanding AF. This finding agrees with the concept that longstanding AF leads to impaired ability of the atria to produce these neurohormones due to inherent degenerative changes.

Caveolin-1/3 double-knockout mice are viable, but lack both muscle and non-muscle caveolae, and develop a severe cardiomyopathic phenotype

The caveolin gene family consists of caveolins 1, 2, and 3. Caveolins 1 and 2 are co-expressed in many cell types, such as endothelial cells, fibroblasts, smooth muscle cells and adipocytes, where they form a heteroligomeric complex. In contrast, the expression of caveolin-3 is muscle-specific. Thus, the expression of caveolin-1 is required for caveolae formation in non-muscle cells, while the expression of caveolin-3 drives caveolae formation in striated muscle cell types (cardiac and skeletal). To create a truly caveolae-deficient mouse, we interbred Cav-1 null mice and Cav-3 null mice to generate Cav-1/Cav-3 double-knockout (Cav-1/3 dKO) mice. Here, we report that Cav-1/3 dKO mice are viable and fertile, despite the fact that they lack morphologically identifiable caveolae in endothelia, adipocytes, smooth muscle cells, skeletal muscle fibers, and cardiac myocytes. We also show that these mice are deficient in all three caveolin gene products, as caveolin-2 is unstable in the absence of caveolin-1. Interestingly, Cav-1/3 dKO mice develop a severe cardiomyopathy. At 2 months of age, analysis of Cav-1/3 dKO hearts via gated magnetic resonance imaging reveals a dramatic increase in left ventricular wall thickness, as compared with Cav-1-KO, Cav-3 KO, and wild-type mice. Further functional analysis of Cav-1/3 dKO hearts via transthoracic echocardiography demonstrates hypertrophy and dilation of the left ventricle, with a significant decrease in fractional shortening. As predicted, Northern analysis of RNA derived from the left ventricle of Cav-1/3 dKO mice shows a dramatic up-regulation of the atrial natriuretic factor message, a well-established biochemical marker of cardiac hypertrophy. Finally, histological analysis of Cav-1/3 dKO hearts reveals hypertrophy, disorganization, and degeneration of the cardiac myocytes, as well as chronic interstitial fibrosis and inflammation. Thus, dual ablation of both Cav-1 and Cav-3 genes in mice leads to a pleiotropic defect in caveolae formation and severe cardiomyopathy.

Myotrophin-kappaB DNA interaction in the initiation process of cardiac hypertrophy

To investigate how cardiac hypertrophy and heart failure develop, we isolated and characterized a candidate initiator, the soluble 12-kDa protein myotrophin, from rat and human hearts. Myotrophin stimulates protein synthesis and myocardial cell growth associated with increased levels of hypertrophy marker genes. Recombinant myotrophin from the cloned gene showed structural/functional motifs, including ankyrin repeats and putative phosphorylation sites for protein kinase C (PKC) and casein kinase II. One repeat, homologous with I kappaB, interacts with rel/NF-kappaB in vitro. We analyzed the interaction of recombinant myotrophin and nuclear extracts prepared from neonatal and adult cardiomyocytes; gel mobility shift assay showed that myotrophin bound to kappaB DNA. To define PKC's role in myotrophin-induced myocyte growth, we incubated neonatal rat myocytes (normal and stretch) with specific inhibitors and found that myotrophin inhibits [3H]leucine incorporation into myocytes and different hypertrophic gene expression in neonatal myocytes. Using confocal microscopy, we observed that a basal level of myotrophin was present in both cytoplasm and nucleus under normal conditions, but under cyclic stretch, myotrophin levels became elevated in the nucleus. Myotrophin gene levels were upregulated when myocytes underwent cyclic stretch or were treated with tumor necrosis factor-alpha (TNF-alpha) or interleukin-1beta and also when excised beating hearts were exposed to high pressure. Our data showed that the myotrophin-kappaB interaction was increased with age in spontaneously hypertensive rats (SHRs) only. Our data provide evidence that myotrophin-kappaB DNA interaction may be an important step in initiating cardiac hypertrophy.

Distinct roles of mitogen-activated protein kinase pathways in GATA-4 transcription factor-mediated regulation of B-type natriuretic peptide gene

The expression of cardiac hormones, atrial natriuretic peptide and B-type natriuretic peptide, is induced by cardiac wall stretch and responds to various hypertrophic agonists such as endothelin-1. In cardiac myocytes, endothelin-1 induces GATA-4 binding to the B-type natriuretic peptide gene, but the signaling pathways involved in endothelin-1-induced GATA-4 activation are unknown. Mitogen-activated protein kinase pathways are stimulated in response to various extracellular stimuli, and they modulate the function of several transcription activators. Here we show that inhibition of p38 kinase with SB203580 inhibited endothelin-1-induced GATA-4 binding to B-type natriuretic peptide gene and serine phosphorylation of GATA-4. Inhibition of extracellular signal-regulated protein kinase with MEK1 inhibitor PD98059 reduced basal and p38-induced GATA-4 binding activity, but it had no significant effect on endothelin-1-induced GATA-4 binding activity. Overexpression of p38 kinase pathway, but not extracellular signal-regulated kinase or c-Jun N-terminal protein kinase, activated GATA-4 binding to B-type natriuretic peptide gene and induced rat B-type natriuretic peptide promoter activity via proximal GATA binding sites. In conclusion, these findings demonstrate that activation of p38 kinase is necessary for hypertrophic agonist-induced GATA-4 binding to B-type natriuretic peptide gene and sufficient for GATA-dependent B-type natriuretic peptide gene expression.

Contractile properties of in situ perfused skeletal muscles from rats with congestive heart failure

We hypothesized that in congestive heart failure (CHF) slow-twitch but not fast-twitch muscles exhibit decreased fatigue resistance in the sense of accelerated reduction of muscle force during activity. Experiments were carried out on anaesthetized rats 6 weeks after induction of myocardial infarction or a sham operation (Sham). Animals with left ventricular end-diastolic pressure (LVEDP) > 15 mmHg under anaesthesia were selected for the CHF group. There was no muscle atrophy in CHF. Force generation by in situ perfused soleus (Sol) or extensor digitorum longus (EDL) muscles was recorded during stimulation (trains at 5 Hz for 6 s (Sol) or 10 Hz for 1.5 s (EDL) at 10 or 2.5 s intervals, respectively) for 1 h in Sol and 10 min in EDL at 37 degrees C. Initial force was almost the same in Sol from CHF and Sham rats, but relaxation was slower in CHF. Relaxation times (95-5 % of peak force) were 177 +/- 55 and 131 +/- 44 ms in CHF and Sham, respectively, following the first stimulation train. After 2 min of stimulation the muscles transiently became slower and maximum relaxation times were 264 +/- 71 and 220 +/- 45 ms in CHF and Sham, respectively (P < 0.05). After 60 min they recovered to 204 +/- 60 and 122 +/- 55 ms in CHF and Sham, respectively (P < 0.05). In CHF but not in Sham rats the force of contraction of Sol declined from the second to the sixtieth minute to 70 % of peak force. The EDL of both CHF and Sham fatigued to 24-28 % of initial force, but no differences in contractility pattern were detected. Thus, slow-twitch muscle is severely affected in CHF by slower than normal relaxation and significantly reduced fatigue resistance, which may explain the sensation of both muscle stiffness and fatigue in CHF patients.

Adenoviral-directed expression of the type 1A angiotensin receptor promotes cardiomyocyte hypertrophy via transactivation of the epidermal growth factor receptor

Angiotensin II (Ang II) may cause cardiac hypertrophy via type 1 Ang II receptors (AT(1)) on cardiomyocytes and through growth factors released from cardiac fibroblasts. Whereas cardiomyocyte-specific AT(1) receptor expression produces cardiac hypertrophy and remodeling in vivo, delineation of the signals that mediate growth to Ang II is challenging because the prevailing in vitro model (cultured neonatal cardiomyocytes) expresses low levels of AT(1) receptor and responds inconsistently to Ang II. In this study, when AT(1A) receptors were expressed using adenovirus in cultured neonatal cardiomyocytes, Ang II stimulated a robust hypertrophy that was not secondary to the release of cardiac fibroblast-derived factors, specifically endothelin-1. Hypertrophy was accompanied by the induction of the immediate-early response genes, c-fos and c-jun, and reexpression of atrial natriuretic peptide (ANP). Ang II-induced activation of an ANP promoter-reporter was inhibited by the dominant/negative mutants, GalphaqI and N17Ras, indicating that hypertrophic signaling by the AT(1A) receptor is via heterotrimeric G protein coupling and downstream Ras pathways. AT(1A)-mediated cardiomyocyte hypertrophy and mitogen-activated protein kinase (MAPK) activation were inhibited by the MAPK kinase inhibitor, PD98059, and the epidermal growth factor (EGF) receptor kinase antagonist, AG1478, but not by PKC inhibitor, bisindolylmaleimide-1. Moreover, Ang II-induced MAPK activation was prevented by treatment with a matrix metalloproteinase inhibitor, consistent with the tyrosine phosphorylation of the EGF receptor in response to AT(1A) receptor activation. These data unequivocally demonstrate that Ang II can directly promote cardiac myocyte growth via AT(1A) receptors expressed on these cells and reveal for the first time the important contribution of EGF receptor-transactivated MAPK signaling to this process.

Interleukin-18 reduces expression of cardiac tumor necrosis factor-alpha and atrial natriuretic peptide in a murine model of viral myocarditis

Heart failure is generally believed to begin with myocyte damage caused by a variety of insults, including ischemia, toxin or myocardial infection. The proinflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha), has been hypothesized to play a pathogenetic role in the transition from compensated to decompensated heart failure. Interleukin-18 (IL-18), a recently cloned cytokine synthesized by Kupffer cells, activates macrophages. We examined the therapeutic effect of IL-18 on the modulation of TNF-alpha gene expression in failing heart in a murine model of heart failure caused by viral myocarditis. The heart weight (HW)/ body weight (BW) ratio in IL-18 treated mice 7 days after viral inoculation was significantly lower (P<0.01) than in the untreated controls. Myocardial necrosis and inflammatory cell infiltration were significantly lower in IL-18 treated mice than untreated mice 5 and 7 days after inoculation. The expression of TNF-alpha mRNA in the myocardium was significantly lower on days 5 and 7 in IL-18 treated mice than in infected untreated mice. We conclude that concurrent systemic administration of IL-18 is beneficial in mice with myocarditis, and may be mediated through reduced expression of TNF-alpha in the heart.

Genomic sequence and cardiac expression of atrial natriuretic peptide in cats

OBJECTIVE

To determine the nucleotide and amino acid sequence of atrial natriuretic peptide (ANP) in cats and its typical regions of cardiac expression.

ANIMALS

5 healthy adult mixed-breed cats.

PROCEDURE

Total RNA was extracted from samples obtained from the left and right atrium, left and right ventricle, and interventricular septum of each cat. The RNA was used to produce cDNA for sequencing and northern blot analysis. Genomic DNA was extracted from feline blood samples. Polymerase chain reaction primers designed from consensus sequences of other species were used to clone and sequence the feline ANP gene.

RESULTS

The feline ANP gene consists of 1,072 nucleotides. It consists of 3 exons (123, 327, and 12 nucleotides) separated by 2 introns (101 and 509 nucleotides). It has several typical features of eukaryotic genes and a putative steroid-response element located within the second intron. Preprohormone ANP consists of 153 amino acids. The amino acid sequence of the active form of feline ANP (ANP-30) is identical to that of equine, bovine, and ovine ANP-30 and differs from that of human, canine, and porcine ANP-28 only by 2 carboxy-terminal arginine residues. The ANP mRNA was detected only in the left and right atria.

CONCLUSIONS AND CLINICAL RELEVANCE

The genetic and protein structure and principal regions of cardiac expression of feline ANP are similar to those of other species. Results of this study should be helpful in future studies on the natriuretic response in cats to diseases that affect cardiovascular function.

Pivotal role of a gp91(phox)-containing NADPH oxidase in angiotensin II-induced cardiac hypertrophy in mice

BACKGROUND

Angiotensin II induces both cardiac and vascular smooth muscle (VSM) hypertrophy. Recent studies suggest a central role for a phagocyte-type NADPH oxidase in angiotensin II-induced VSM hypertrophy. The possible involvement of an NADPH oxidase in the development of cardiac hypertrophy has not been studied. Methods and Results- Mice with targeted disruption of the NADPH oxidase subunit gp91(phox) (gp91(phox-/-)) and matched wild-type mice were subjected to subcutaneous angiotensin II infusion at a subpressor dose (0.3 mg/kg/day) for 2 weeks. Systolic blood pressure was unaltered by angiotensin II in either group. Angiotensin II significantly increased heart/body weight ratio, atrial natriuretic factor and beta-myosin heavy chain mRNA expression, myocyte area, and cardiac collagen content in wild-type but not gp91(phox-/-) mice. Angiotensin II treatment increased myocardial NADPH oxidase activity in wild-type but not gp91(phox-/-) mice.

CONCLUSIONS

A gp91(phox)-containing NADPH oxidase plays an important role in the development of angiotensin II-induced cardiac hypertrophy, independent of changes in blood pressure.

Dominant negative mutant of c-Jun inhibits cardiomyocyte hypertrophy induced by endothelin 1 and phenylephrine

The activator protein 1 (AP-1) transcriptional complex, containing Jun and Fos proteins, is involved in regulating many cellular processes such as proliferation and differentiation. However, little is known about a direct relationship between AP-1 activities and cardiomyocyte hypertrophy. To elucidate the roles of myocardial AP-1 activities, dominant negative mutant of c-Jun (DNJun) was overexpressed in cultured rat neonatal ventricular myocytes by adenovirus vector to abrogate endogenous AP-1 activation. Cardiomyocytes were treated with 100 nmol/L endothelin 1 (ET) and 10 micromol/L phenylephrine (PE) to induce myocardial cell hypertrophy. Both ET and PE significantly enhanced AP-1 DNA binding activities (3.4-fold by ET and 4.8-fold by PE at 3 hours, P<0.01). At 48 hours after stimulation, ET and PE significantly increased incorporation of (3)H-phenylalanine (1.4-fold by ET and 1.5-fold by PE, P<0.01), cell size (2.3-fold and 2.5-fold, P<0.01), and mRNA expression of atrial natriuretic peptide (ANP; 1.9-fold and 1.8-fold, P<0.01) and brain natriuretic peptide (BNP; 1.6-fold and 1.6-fold, P<0.01). Adenovirus carrying DNJun prevented the transcriptional activation of the AP-1 by ET and PE, using AP-1 reporter enzyme firefly luciferase assay. Moreover, DNJun prevented the increase in incorporation of (3)H-phenylalanine, cell size, and the mRNA expression of ANP and BNP by ET and PE. In conclusion, we provide the first evidence that DNJun inhibits cardiomyocyte hypertrophy through inhibition of AP-1 transcriptional activity.

Chronic exposure to carbon monoxide and nicotine: endothelin ET(A) receptor antagonism attenuates carbon monoxide-induced myocardial hypertrophy in rat

The aims of the present study were to determine the effects of endothelin ET(A) receptor antagonism on carbon monoxide (CO)-induced cardiac hypertrophy and endothelin-1 (ET-1) expression and to compare myocardial effects of chronic nicotine with CO exposure. Female Sprague-Dawley rats (n = 84) were randomized to three groups exposed 20 h/day to CO (200 ppm), nicotine (500 microg/m3), or air for 14 consecutive days. In each exposure group, animals were randomized to ET(A) receptor antagonist LU 135252 in drinking water (0.5 mg/ml) or placebo. Myocardial ET-1 and atrial natriuretic peptide (ANP) expression was measured by competitive RT-PCR and plasma ET-1 by immunoassay. Carboxyhemoglobin was 22.1 +/- 0.3% in CO-exposed animals and 2.8 +/- 0.3% in controls. Plasma nicotine was 57 +/- 7 ng/ml and plasma cotinine was 590 +/- 23 ng/ml in nicotine-exposed animals and below detection levels in controls. CO exposure induced a 21% increase in right ventricular hypertrophy (p < 0.01), a 7% increase in left ventricular hypertrophy (p < 0.01), a 25% increase in right ventricular ET-1 expression (p < 0.05), and an eightfold increase in ANP expression (p = 0.08). ET(A) receptor antagonism reduced right ventricular hypertrophy by 60% (p < 0.05) with no significant effect on left ventricular hypertrophy or myocardial ET-1 expression. Chronic nicotine exposure did not significantly affect cardiac weights or ANP and ET-1 expression. We conclude that ET(A) receptor antagonism reduces right ventricular hypertrophy induced by chronic CO exposure, whereas CO-induced myocardial ET-1 expression remains unchanged.

Pressure overload induces heterologous expression of the atrial natriuretic factor (ANF) gene

Several investigations have demonstrated the regional heterogeneity of myocardial phenotype, and hypertrophy may also induce regionally disparate changes. We have utilized the direct DNA injection technique to study regional variations in overload-induced ANF expression. Pressure overload was induced by stenosis of the ascending aorta in canines. ANF promoter reporters were injected into the left ventricle; in different regions including the base, the midwall region, and the apex. Injections were made at different depths to include the epicardial and endocardial layers. The animals were sacrificed 7 days following surgery and the left ventricle harvested for tissue analysis. Under normotensive conditions, ANF reporter expression was similar throughout the heart. PO increased ANF expression and the increases were greater in the endocardium than in the epicardium. PO also significantly increased expression in the midwall and base regions, but not in the apex. It is unknown from these experiments, whether the greater increases in midwall expression are a function of greater wall stress, metabolic demand, or phenotypic differences in the midwall myocytes. These findings do indicate that regional differences in overload-induced changes in gene expression are evident and may be functionally important in determining myocardial response to increased functional demand.

[High level expression of human atrial natriuretic peptide in fusion form in E. coli system]

OBJECTIVE

To construct recombinant plasmid with human atrial natriuretic peptide (ANP) gene in fusion form for stable and high level expression of genetic engineering product ANP in E. coli system.

METHODS

Plasmids with ANP fusion gene were constructed by PCR and sub-cloning and fusion protein was expressed in E. coli system. High level expression of the fusion genes was enhanced by linking operons in tandem. ANP was released from the fusion protein with thrombin treatment and purified by chromatography. Genetic-engineered ANP was evaluated with the drug production requirement, and produced ANP was tested for its effects of lowering blood pressure and diuresis in vivo and vasodilation in vitro.

RESULTS

A series of 4 plasmid pCW111-114, containing 1 to 4 gene operons respectively, were constructed, and the yields of fusion protein were 46%, 54.8%, 56.1% and 60.1% of total cell protein. Fusion protein in the form of inclusion body was isolated and purified, and then treated with thrombin to release ANP. After purification using chromatography columns, at least 3 mg/L culture of ANP with the purity higher than 96% was produced in shaking flask. Primary pharmacological evaluation showed the produced ANP had the effects of blood pressure lowering in vivo and diuresis in vivo and vasodilation in vitro, which was similar to the activity of standard ANP.

CONCLUSIONS

By the protocol of fusion gene cloning and expression, the human ANP was produced successfully in E. coli system.

Calcium handling and sarcoplasmic-reticular protein functions during heart-failure transition in ventricular myocardium from rats with hypertension

The objective of this study was to determine the primary event that occurs in Ca2+-regulatory sarcoplasmic-reticular (SR) proteins during subacute transition from concentric/mechanically-compensated left ventricular (LV) hypertrophy to eccentric/decompensated hypertrophy. Using Dahl salt-sensitive rats with hypertension, changes of myocardial contraction, intracellular Ca2+ transients, SR Ca2+ uptake, protein levels of SR Ca2+ ATPase (SERCA2), phospholamban, and calsequestrin (CSQ), and mRNA levels of SERCA2 and CSQ were serially determined and compared between the established stage of LV hypertrophy (LVH) and the subsequent stage of overt LV dysfunction (CHF). In LVH, isolated LV papillary muscle preparations showed an equal peak-tension level and a mild prolongation of the isometric tension decay compared to those of age-matched controls. The Ca2+ transients as measured by aequorin were unchanged. The Ca2+ uptake of isolated SR vesicles and the protein/mRNA levels of SR proteins were also equivalent to those of the controls. In contrast, in CHF, the failing myocardium showed a further prolongation of the contraction time course and a 39% reduction of the peak-tension development. The Ca2+ transients showed changes consisting of a decrease in the peak level and a prolongation of the time course. In addition, the SR Ca2+ uptake was decreased by 41%. Despite these functional changes, the protein and mRNA levels of the SR components remained equivalent to those of the age-matched controls. Thus, in this hypertensive animal, 1) at the LVH stage, myocardial contractility and intracellular capability to regulate Ca2+ remained normal; 2) at the CHF stage, impaired SR Ca2+ handling and the subsequent reduction of myocardial contraction were in progress; and 3) impairments of SR function occurred at the post-translational protein level rather than at the transcriptional/translational levels. Our findings support the role of SR proteins as the primary determinant of the contractile dysfunction that occurs during the heart-failure transition; however, post-translational modulators of these SR elements may also be critical.

Cardiac gene expression and synthesis of atrial natriuretic peptide in the nitrofen model of congenital diaphragmatic hernia in rats: effect of prenatal dexamethazone treatment

BACKGROUND/PURPOSE

The aim of this study was to determine the gene and protein levels of atrial natriuretic peptide (ANP) in the heart of nitrofen-induced congenital diaphragmatic hernia (CDH) in rats and to evaluate the effect of antenatal dexamethazone (Dex) treatment.

METHODS

CDH model was induced in pregnant rats after administration of 100 mg of nitrofen on day 9.5 of gestation (term, day 22). Dexamethazone (Dex, 0.25 mg/kg) was given by intraperitoneal injection on days 18.5 and 19.5 of gestation. Cesarean section was performed on day 21 of gestation. The fetuses were divided into 3 groups: group I, control (n = 10); group II, nitrofen-induced CDH (n = 10); group III, nitrofen-induced CDH with antenatal Dex treatment (n = 10). ANP protein was measured using enzyme-linked immunosorbent assay (ELISA) technique. Reverse transcription polymerase chain reaction (RT-PCR) was performed to evaluate the relative amount of atrial natriuretic peptide (ANP) mRNA expression.

RESULTS

There was a significant reduction in ANP mRNA (P <.05) and protein (P <.01) levels in heart of group II (CDH) compared with group I. Antenatal Dex treatment significantly increased both ANP mRNA and protein levels in the heart of CDH animals (P <.05).

CONCLUSIONS

The reduced cardiac ANP gene expression and ANP synthesis indicates that the heart in CDH is functionally immature and may be unable to respond to hemodynamic load accompanying persistent pulmonary hypertension (PPH). ANP or drugs such as steroids, which raise endogenous ANP levels, may have a therapeutic application in CDH complicated by PPH.

Atrial natriuretic peptide (ANP) system in frog skin

In this study the ultrastructure of Rana esculenta skin is described. Cytochemical methods were used to localize guanylate cyclase in the presence of atrial natriuretic peptide and immunocytochemical methods showed the presence of the atrial natriuretic peptide in various levels of skin. The peptide is mainly found in the epithelium and in the lymph sacs of the tela subcutanea. Its receptors are located in the same zones and are indicated by guanylate cyclase activity. We demonstrate that frog skin is a target organ for atrial natriuretic peptide and propose that, at this level, the peptide carries out an important osmoregulatory role.

Attenuation of compensatory right ventricular hypertrophy and heart failure following monocrotaline-induced pulmonary vascular injury by the Na+-H+ exchange inhibitor cariporide

Pulmonary hypertension results in compensatory right ventricular (RV) hypertrophy. We studied the role of the Na+-H+ exchange (NHE) in the latter process by determining the effect of the NHE-1 inhibitor cariporide after monocrotaline-induced pulmonary artery injury. Sprague-Dawley rats received a control or cariporide diet for 7 days, at which time they were administered either monocrotaline (60 mg/kg) or its vehicle. Twenty-one days later, monocrotaline control, but not cariporide-fed animals, demonstrated increased RV weights and cell size of 65 and 52%, respectively. Monocrotaline alone significantly increased RV systolic pressure and end diastolic pressure by 70 and 94%, respectively, whereas corresponding values with cariporide were significantly reduced to 33 and 42%. Central venous pressure increased by 414% in control animals, which was significantly reduced by cariporide. Monocrotaline treatment produced a decrease in cardiac output of 28 and 8% in the absence or presence of cariporide (P < 0.05 between groups), respectively. Although body weights were significantly lower in both monocrotaline-treated groups compared with vehicle treatment, with cariporide the net gain in body weight was twice that seen in the monocrotaline-treated animals without cariporide. Monocrotaline also increased RV NHE-1 and atrial natriuretic peptide mRNA expression, which was abrogated by cariporide. Monocrotaline-induced myocardial necrosis, fibrosis, and mononuclear infiltration was completely prevented by cariporide. Cariporide had no effect on monocrotaline-induced pulmonary intimal wall thickening. Our results demonstrate that cariporide directly attenuates myocardial dysfunction after monocrotaline administration independent of pulmonary vascular effects. NHE-1 inhibition may represent an effective adjunctive therapy that selectively targets myocardial hypertrophic responses in pulmonary vascular injury.

Regulation of the ANF and BNP promoters by GATA factors: lessons learned for cardiac transcription

The identification and molecular cloning of the cardiac transcription factors GATA-4, -5, and -6 has greatly contributed to our understanding of how tissue-specific transcription is achieved during cardiac growth and development. Through analysis of their interacting partners, it has also become apparent that a major mechanism underlying spatial and temporal specificity within the heart as well as in the response to cardiogenic regulators is the combinatorial interaction between cardiac-restricted and inducible transcription factors. The cardiac GATA factors appear to be fundamental contributors to these regulatory networks. Two of the first targets identified for the cardiac GATA factors were the natriuretic peptide genes encoding atrial natriuretic factor (ANF) and B-type natriuretic peptide (BNP), the major heart secretory products that are also accepted clinical markers of the diseased heart. Studies using the ANF and BNP promoters as models of cardiac-specific transcription have unraveled the pivotal role that GATA proteins play in cardiac gene expression. We review the current knowledge on the modulation of the natriuretic peptide promoters by GATA factors, including examples of combinatorial interactions between GATA proteins and diverse transcription factors.

Regional expression of endothelin-1, ANP, IGF-1, and LV wall stress in the infarcted rat heart

We hypothesized that myocardial infarction induces regional and temporal differences in endothelin-1 (ET-1), atrial natriuretic peptide (ANP), and insulin-like growth factor-1 (IGF-1) gene expression that correlate with left ventricular (LV) wall stress. Echocardiography and LV pressure measurements were performed in coronary artery-ligated or sham-operated rats. Gene expression was measured by competitive RT-PCR in the infarct, border zone, and remote area and in regionally isolated cardiomyocytes. ET-1 and IGF-1 expression was highest in the infarcted myocardium, whereas ANP expression was highest in noninfarcted myocardium. For all genes, remote area expression was highest after 7 days. At 42 days, ANP maintained maximum expression, ET-1 decreased to 50% of peak levels, and IGF-1 was normalized. Cardiomyocyte expression followed the same pattern as in the myocardium except for a markedly lower IGF-1 expression. Diastolic wall stress was the best hemodynamic variable to predict ET-1 and ANP expression in the remote area. We conclude that ET-1, ANP, and IGF-1 are expressed in different patterns in the infarcted heart in relation to time, functional regions, cellular distribution, and mechanical load.

Increased expression of atrial natriuretic peptide in ureteral obstructed kidneys in rats

OBJECTIVES

Whether the natriuresis in the previously ureteral obstructed kidney may be related to an altered regulation of local atrial natriuretic peptide (ANP) was investigated.

MATERIALS AND METHODS

Male Sprague-Dawley rats were unilaterally obstructed of the left ureters for 48 hours. The left and right ureters were separately cannulated to collect urine samples. In some rats, both kidneys were removed without releasing the obstruction. Control rats were treated the same except that no ureteral obstruction was made. The mRNA expression of ANP and natriuretic peptide receptor (NPR)-A was determined in the kidney by reverse transcription-polymerase chain reaction. The guanylyl cyclase activity was measured by the amount of cGMP generated in response to ANP. Plasma levels of ANP were measured by radioimmunoassay.

RESULTS

The ureteral obstruction did not significantly affect the plasma ANP levels. In the obstructed kidney, the creatinine clearance was decreased, while the fractional excretion of sodium increased. The expression of ANP mRNA was increased in the obstructed kidney. The NPR-A mRNA expression was not altered in the glomerulus, but was decreased in the papilla of the obstructed kidney. Nor was the guanylyl cyclase activity in the glomerulus altered. Although the guanylyl cyclase activity in the papilla was significantly decreased in the obstructed kidney, it was rapidly resumed upon releasing the obstruction.

CONCLUSIONS

An increased local expression of ANP may, at least in part, account for the natriuresis in the previously ureteral obstructed kidney.

Endothelin-1, endothelin-1 receptors and cardiac natriuretic peptides in failing human heart

Endothelin (ET)-1 is a potent vasoconstrictor peptide produced in the myocardium that can exert important effects on cardiac myocyte growth and phenotype; cardiac natriuretic peptides (ANP and BNP) are known to act as physiological antagonists of ET-1. In this study a comparative determination of ET-1 receptors and of the local productions of ET-1 and of ANP and BNP was made in different sites of failing and nonfailing hearts. Tissue from right and left atrium, right and left ventricle and interventricular septum from seven adult heart transplant recipients with end-stage idiopathic dilated cardiomyopathy (functional class III and IV, with ejection fraction < 35%) and from four postmortem subjects without cardiac complications was analyzed. In failing hearts we observed a tendency to increase of density of binding sites, most evident in left ventricle (62.6+/-22.6 fmol/mg protein vs. 29.0+/-3.3, mean +/- SEM, p = ns). A prevalence of ET-A subclass, observed in all samples, resulted more pronounced in failing hearts where this increase, found in all the cardiac regions, was more evident in left ventricle (p = 0.0007 vs nonfailing hearts). The local concentrations of ET-1, ANP and BNP resulted significantly increased in failing hearts with respect to controls in all sides of the heart. In failing hearts we have observed a tendency to increase in endothelin receptor density mainly due to a significant upregulation of ET-A subtype and a parallel increase of the tissue levels of ANP, BNP and ET-1 indicating an activation of these systems in heart failure.

Regional cardiac expression and concentration of natriuretic peptides in patients with severe chronic heart failure

The purpose of this study was to examine the regional cardiac mRNA expression and concentration of brain natriuretic peptide (BNP) and atrial natriuretic peptide (ANP) in relation to the circulating peptide concentrations in patients with chronic heart failure (CHF). The myocardial mRNA levels and peptide concentrations of BNP and ANP were analysed in seven different regions of the heart from patients undergoing cardiac transplantation. Autopsy samples from individuals without known cardiovascular disease were used as controls. The plasma levels of natriuretic peptides and their N-terminal propeptides, Nt-proBNP and Nt-proANP, were measured in the CHF patients and healthy volunteers. In the autopsy specimens, the atrial regions appeared to contain the highest peptide levels for BNP as well as ANP, the atrioventricular ratio being 12-262 and 72-637-fold, respectively. In the CHF patients there was a relative shift towards the ventricle for BNP, reducing the atrioventricular ratio to 6-16-fold. The circulating concentrations of BNP/Nt-proBNP in the CHF patients correlated closely to the BNP mRNA expression in most myocardial regions including the left ventricle (r = 0.72, P < 0.001). For circulating concentrations of ANP/Nt-proANP, such correlation were limited to the left atrium free wall (r = .66, P < 0.002). Thus, of the two natriuretic peptides, BNP/Nt-proBNP may be a better reflector of left ventricular overload.

Rescue of contractile parameters and myocyte hypertrophy in calsequestrin overexpressing myocardium by phospholamban ablation

Cardiac-specific overexpression of murine cardiac calsequestrin results in depressed cardiac contractile parameters, low Ca(2+)-induced Ca(2+) release from sarcoplasmic reticulum (SR) and cardiac hypertrophy in transgenic mice. To test the hypothesis that inhibition of phospholamban activity may rescue some of these phenotypic alterations, the calsequestrin overexpressing mice were cross-bred with phospholamban-knockout mice. Phospholamban ablation in calsequestrin overexpressing mice led to reversal of the depressed cardiac contractile parameters in Langendorff-perfused hearts or in vivo. This was associated with increases of SR Ca(2+) storage, assessed by caffeine-induced Na(+)-Ca(2+) exchanger currents. The inactivation time of the L-type Ca(2+) current (I(Ca)), which has an inverse correlation with Ca(2+)-induced SR Ca(2+) release, and the relation between the peak current density and half-inactivation time were also normalized, indicating a restoration in the ability of I(Ca) to trigger SR Ca(2+) release. The prolonged action potentials in calsequestrin overexpressing cardiomyocytes also reversed to normal upon phospholamban ablation. Furthermore, ablation of phospholamban restored the expression levels of atrial natriuretic factor and alpha-skeletal actin mRNA as well as ventricular myocyte size. These results indicate that attenuation of phospholamban function may prevent or overcome functional and remodeling defects in hypertrophied hearts.