Opening of the adenosine triphosphate-sensitive potassium channel attenuates cardiac remodeling induced by long-term inhibition of nitric oxide synthesis: role of 70-kDa S6 kinase and extracellular signal-regulated kinase

Cardiac-specific Trim44 knockout in rat attenuates isoproterenol-induced cardiac remodeling via inhibition of AKT/mTOR pathway

When pathological hypertrophy progresses to heart failure (HF), the prognosis is often very poor. Therefore, it is crucial to find new and effective intervention targets. Here, myocardium-specific Trim44 knockout rats were generated using CRISPR-Cas9 technology. Cardiac phenotypic observations revealed that Trim44 knockout affected cardiac morphology at baseline. Rats with Trim44 deficiency exhibited resistance to cardiac pathological changes in response to stimulation via isoproterenol (ISO) treatment, including improvement of cardiac remodeling and dysfunction by morphological and functional observations, reduced myocardial fibrosis and reduced expression of molecular markers of cardiac stress. Furthermore, signal transduction validation associated with growth and hypertrophy development in vivo and in vitro demonstrated that Trim44 deficiency inhibited the activation of signaling pathways involved in myocardial hypertrophy, especially response to pathological stress. In conclusion, the present study indicates that Trim44 knockout attenuates ISO-induced pathological cardiac remodeling through blocking the AKT/mTOR/GSK3β/P70S6K signaling pathway. This is the first study to demonstrate the function and importance of Trim44 in the heart at baseline and under pathological stress. Trim44 could be a novel therapeutic target for prevention of cardiac hypertrophy and HF.

Summary: This is the first study to demonstrate the function of Trim44 in the heart at baseline and under pathological stress. Trim44 could be a novel therapeutic target for prevention of cardiac hypertrophy.

Nicorandil prevents right ventricular remodeling by inhibiting apoptosis and lowering pressure overload in rats with pulmonary arterial hypertension

Background

Most of the deaths among patients with severe pulmonary arterial hypertension (PAH) are caused by progressive right ventricular (RV) pathological remodeling, dysfunction, and failure. Nicorandil can inhibit the development of PAH by reducing pulmonary artery pressure and RV hypertrophy. However, whether nicorandil can inhibit apoptosis in RV cardiomyocytes and prevent RV remodeling has been unclear.

Methodology/Principal Findings

RV remodeling was induced in rats by intraperitoneal injection of monocrotaline (MCT). RV systolic pressure (RVSP) was measured at the end of each week after MCT injection. Blood samples were drawn for brain natriuretic peptide (BNP) ELISA analysis. The hearts were excised for histopathological, ultrastructural, immunohistochemical, and Western blotting analyses. The MCT-injected rats exhibited greater mortality and less weight gain and showed significantly increased RVSP and RV hypertrophy during the second week. These worsened during the third week. MCT injection for three weeks caused pathological RV remodeling, characterized by hypertrophy, fibrosis, dysfunction, and RV mitochondrial impairment, as indicated by increased levels of apoptosis. Nicorandil improved survival, weight gain, and RV function, ameliorated RV pressure overload, and prevented maladaptive RV remodeling in PAH rats. Nicorandil also reduced the number of apoptotic cardiomyocytes, with a concomitant increase in Bcl-2/Bax ratio. 5-hydroxydecanoate (5-HD) reversed these beneficial effects of nicorandil in MCT-injected rats.

Conclusions/Significance

Nicorandil inhibits PAH-induced RV remodeling in rats not only by reducing RV pressure overload but also by inhibiting apoptosis in cardiomyocytes through the activation of mitochondrial ATP-sensitive K⁺ (mitoK_ATP) channels. The use of a mitoK_ATP channel opener such as nicorandil for PAH-associated RV remodeling and dysfunction may represent a new therapeutic strategy for the amelioration of RV remodeling during the early stages of PAH.

Phosphoprotein abundance changes in hypertensive cardiac remodeling

There is over-whelming evidence that protein phosphorylations regulate cardiac function and remodeling. A wide variety of protein kinases, e.g., phosphoinositide 3-kinase (PI3K), Akt, GSK-3, TGFβ, and PKA, MAPKs, PKC, Erks, and Jaks, as well as phosphatases, e.g., phosphatase I (PP1) and calcineurin, control cardiomyocyte growth and contractility. In the present work, we used global phosphoprotein profiling to identify phosphorylated proteins associated with pressure overload (PO) cardiac hypertrophy and heart failure. Phosphoproteins from hypertrophic and systolic failing hearts from male hypertensive Dahl salt-sensitive rats, trans-aortic banded (TAC), and spontaneously hypertensive heart failure (SHHF) rats were analyzed. Profiling was performed by 2-dimensional difference in gel electrophoresis (2D-DIGE) on phospho-enriched proteins. A total of 25 common phosphoproteins with differences in abundance in (1) the 3 hypertrophic and/or (2) the 2 systolic failure heart models were identified (CI>99%) by matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) and Mascot analysis. Among these were (1) myofilament proteins, including alpha-tropomyosin and myosin regulatory light chain 2, cap Z interacting protein (cap ZIP), and tubulin β5; (2) mitochondrial proteins, including pyruvate dehydrogenase α, branch chain ketoacid dehydrogenase E1, and mitochondrial creatine kinase; (3) phosphatases, including protein phosphatase 2A and protein phosphatase 1 regulatory subunit; and (4) other proteins including proteosome subunits α type 3 and β type 7, and eukaryotic translation initiation factor 1A (eIF1A). The results include previously described and novel phosphoproteins in cardiac hypertrophy and systolic failure.

K(ATP) channels mediate the antihypertrophic effects afforded by κ-opioid receptor stimulation in neonatal rat ventricular myocytes

Recent evidence suggests that κ-opioid receptor (OR) agonists and K(ATP) channel activation exert antihypertrophic effects on cardiac myocytes. We studied the role of K(ATP) channels in the antihypertrophic effects of ORs in primary cultures of neonatal rat ventricular myocytes exposed for 48 h to the α(1) adrenoceptor agonist phenylephrine and the relative contributions of mitochondrial K(ATP) (mitoK(ATP)) and sarcolemmal K(ATP) (sarcK(ATP)). Furthermore, we elucidated the pathway between ORs and K(ATP) channels and their impact on intracellular Ca(2+) ([Ca(2+)](i)) transients. Hypertrophy of cardiomyocytes was characterized by increases in i) total protein content; ii) cell size and iii) [(3)H]leucine incorporation. Phenylephrine (10 μM) increased the three parameters. Trans-(±)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]-benzeneacetamid methanesulfonate salt (U50,488H), a selective κ-opioid receptor agonist, prevented phenylephrine-induced hypertrophy and [Ca(2+)](i) transients. The effect of U50,488H was abolished by nor-binaltorphimine, a selective κ-OR antagonist, indicating that the effect was κ-OR-mediated. The protein kinase C inhibitor chelerythrine and the K(ATP) channel inhibitors glibenclamide (50 μM), a nonselective K(ATP) antagonist, and 5-hydroxydecanoic acid (100 μM), a mitochondrial selective K(ATP) antagonist, reversed the antihypertrophic effect of U50,488H, and there was no significant difference between the two K(ATP) channel blockers. Moreover, we also determined the expression of the Kir6.2 subunits of the K(ATP) channel, which increased in response to U50,488H in the presence of phenylephrine, but was suppressed by chelerythrine, glibenclamide and 5-hydroxydecanoic acid. U50,488H also attenuated the elevation of [Ca(2+)](i). This study suggests that K(ATP), and particularly the mitochondrial K(ATP,) mediates the antihypertrophic effects of κ-opioid receptor stimulation via the PKC signaling pathway.

Pathophysiology of myocardial reperfusion injury: preconditioning, postconditioning, and translational aspects of protective measures

Heart diseases due to myocardial ischemia, such as myocardial infarction or ischemic heart failure, are major causes of death in developed countries, and their number is unfortunately still growing. Preliminary exploration into the pathophysiology of ischemia-reperfusion injury, together with the accumulation of clinical evidence, led to the discovery of ischemic preconditioning, which has been the main hypothesis for over three decades for how ischemia-reperfusion injury can be attenuated. The subcellular pathophysiological mechanism of ischemia-reperfusion injury and preconditioning-induced cardioprotection is not well understood, but extensive research into components, including autacoids, ion channels, receptors, subcellular signaling cascades, and mitochondrial modulators, as well as strategies for modulating these components, has made evolutional progress. Owing to the accumulation of both basic and clinical evidence, the idea of ischemic postconditioning with a cardioprotective potential has been discovered and established, making it possible to apply this knowledge in the clinical setting after ischemia-reperfusion insult. Another a great outcome has been the launch of translational studies that apply basic findings for manipulating ischemia-reperfusion injury into practical clinical treatments against ischemic heart diseases. In this review, we discuss the current findings regarding the fundamental pathophysiological mechanisms of ischemia-reperfusion injury, the associated protective mechanisms of ischemic pre- and postconditioning, and the potential seeds for molecular, pharmacological, or mechanical treatments against ischemia-reperfusion injury, as well as subsequent adverse outcomes by modulation of subcellular signaling mechanisms (especially mitochondrial function). We also review emerging translational clinical trials and the subsistent clinical comorbidities that need to be overcome to make these trials applicable in clinical medicine.

Regulation of mRNA translation as a conserved mechanism of longevity control

Appropriate regulation of mRNA translation is essential for growth and survival and the pathways that regulate mRNA translation have been highly conserved throughout eukaryotic evolution. Translation is controlled by a complex set of mechanisms acting at multiple levels, ranging from global protein synthesis to individual mRNAs. Recently, several mutations that perturb regulation of mRNA translation have also been found to increase longevity in three model organisms: the buddingyeast Saccharomyces cerevisiae, the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster. Many of these translation control factors can be mapped to a single pathway downstream of the nutrient responsive target of rapamycin (TOR) kinase. In this chapter, we will review the data suggesting that mRNA translation is an evolutionarily conserved modifier of longevity and discuss potential mechanisms by which mRNA translation could influence aging and age-associated disease in different species.

The TOR pathway comes of age

Studies in a variety of model organisms indicate that nutrient signaling is tightly coupled to longevity. In nutrient replete conditions, organisms develop, grow, and age quickly. When nutrients become sparse as with dietary restriction, growth and development decline, stress response pathways become induced and organisms live longer. Considerable effort has been devoted to understanding the molecular events mediating lifespan extension by dietary restriction. One central focus has been on nutrient-responsive signal transduction pathways including insulin/IGF-1, AMP kinase, protein kinase A and the TOR pathway. Here we describe the increasingly prominent links between TOR signaling and aging in invertebrates. Longevity studies in mammals are not published to date. Instead, we highlight studies in mouse models, which indicate that dampening the TOR pathway leads to widespread protection from an array of age-related diseases.

Effect of ATP-sensitive potassium channel agonists on ventricular remodeling in healed rat infarcts

OBJECTIVES

The purpose of this study was to determine whether ATP-sensitive potassium (K(ATP)) channel agonists exert a beneficial effect on the structural, functional, and molecular features of the remodeling heart in infarcted rats.

BACKGROUND

Myocardial K(ATP) channels have been implicated in the ventricular remodeling after myocardial infarction by inhibition of 70-kDa S6 (p70S6) kinase.

METHODS

Male Wistar rats after induction of myocardial infarction were randomized to either vehicle, agonists of K(ATP) channels nicorandil and pinacidil, an antagonist of K(ATP) channels glibenclamide, or a combination of nicorandil and glibenclamide or pinacidil and glibenclamide for 4 weeks. To verify the role of p70S6 kinase in ventricular remodeling, rapamycin was also assessed.

RESULTS

Significant ventricular hypertrophy was detected by increased myocyte size at the border zone isolated by enzymatic dissociation after infarction. Increased synthesis of p70S6 kinase messenger ribonucleic acid after infarction in vehicle-treated rats was confirmed by reverse transcription-polymerase chain reaction, consistent with the results of immunohistochemistry and Western blot for phosphorylated p70S6 kinase. Rats in the nicorandil- and pinacidil-treated groups significantly attenuated cardiomyocyte hypertrophy and phosphorylated p70S6 kinase expression with similar potency, as compared with vehicle. The beneficial effects of nicorandil and pinacidil were abolished by administering either glibenclamide or 5-hydroxydecanoate. Addition of rapamycin attenuated ventricular remodeling and did not have additional beneficial effects compared with those seen in rats treated with either nicorandil or pinacidil alone.

CONCLUSIONS

Activation of K(ATP) channels by either nicorandil or pinacidil can attenuate ventricular remodeling, probably through a p70S6 kinase-dependent pathway after infarction.

Reduction of protein synthesis and statin-induced cardiomyocyte cell death

The objective of this study was to determine whether an HMG Co A reductase inhibitor (statin) reduces protein synthesis in cardiomyocytes and whether this action maybe an underlying mechanism for statin-induced cell death. Cardiomyocytes from embryonic chick heart were maintained in culture. Cells exposed to lovastatin for 4 h showed a concentration dependent reduction in protein synthesis as assessed by [3H] leucine incorporation and [35S] methionine incorporation. Compared to control, lovastatin 100 microM, which produced a 25% increase in cell death, induced a three-fold reduction in methionine incorporation. [35S] methionine autoradiography showed little (new) protein synthesis at concentrations of lovastatin of 70 microM or higher; an effect that was not limited to specific proteins. Cardiomyocytes treated with lovastatin showed morphologic changes in the nucleoli consistent with insufficient protein synthesis. These cardiomyocytes manifested cell death under conditions of reduced protein synthesis. Interruption of protein synthesis with cycloheximide, a ribosomal RNA transcription inhibitor or reduction in protein substrate availability by lowering the media concentration of fetal calf serum was associated with a concentration-dependent reductions in cell viability. Importantly, stimulation of protein synthesis by higher concentrations of fetal calf serum limited lovastatin-induced cell death. These data suggest that statin-induced inhibition of protein synthesis is an underlying mechanism for statin-induced cell death.

Effect of pravastatin on left ventricular mass in the two-kidney, one-clip hypertensive rats

We have demonstrated that myocardial ATP-sensitive potassium (KATP) channels are implicated in the development of cardiac hypertrophy in hyperlipidemic rabbits. We investigated the effect of pravastatin on development of ventricular hypertrophy in male normolipidemic Wistar rats with two-kidney, one-clip (2K1C) hypertension and whether the attenuated hypertrophic effect was via activation of KATPchannels. Twenty-four hours after the left renal artery was clipped, rats were treated with one of the following therapies for 8 wk: vehicle, nicorandil (an agonist of KATPchannels), pravastatin, glibenclamide (an antagonist of KATPchannels), hydralazine, nicorandil plus glibenclamide, or pravastatin plus glibenclamide. Systolic blood pressure, relative left ventricular (LV) weight, and cardiomyocyte sizes significantly increased in vehicle-treated 2K1C rats compared with those in sham-operated rats. Treatment with either nicorandil or pravastatin significantly attenuated LV hypertrophy/body weight compared with the vehicle, which was further confirmed by downregulation of LV atrial natriuretic peptide mRNA. Nicorandil-induced effects were abolished by administering glibenclamide. Similarly, pravastatin-induced beneficial effects were reversed by the addition of glibenclamide, implicating KATPchannels as the relevant target. A dissociation between the effects of blood pressure and cardiac structure was noted because pravastatin and hydralazine reduced arterial pressure similarly. These results suggest a crucial role of cardiac KATPchannel system in the development of ventricular hypertrophy in the 2K1C hypertensive rats. Pravastatin is endowed with cardiac antihypertrophic properties probably through activation of KATPchannels, independent of lipid and hemodynamic changes.

Association of gliclazide and left ventricular mass in type 2 diabetic patients

Diabetes is a state of increased oxidant stress and there is evidence that oxidation may play a role in the genesis of higher left ventricular mass. Gliclazide has been shown to possess free radical scavenging properties. We assessed whether gliclazide may have a beneficial effect on left ventricular mass via reducing 8-iso-prostaglandin F(2alpha) concentrations, a reliable marker of oxidant injury. A total of 41 patients were randomized into two groups. All patients had been taking glibenclamide for more than 3 months before being randomized to switch either an equipotent dose of gliclazide (n=21) or to continue on glibenclamide (n=20). Baseline characteristics were similar in both groups. At 6 months, gliclazide-treated patients showed a significant regression in left ventricular mass index compared with the glibenclamide-treated group (-16% versus 3%, P=0.003). Gliclazide patients had significantly lower plasma 8-iso-prostaglandin F(2alpha) compared with baseline (299+/-101 pg/ml versus 400+/-112 pg/ml, P=0.001) and the glibenclamide-treated patients (299+/-101 pg/ml versus 388+/-114 pg/ml, P=0.01) after 6-month therapy. The magnitude of left ventricular mass index regression correlated univariately with the magnitude of inhibition of 8-iso-prostaglandin F(2alpha) formation (r=0.74, P<0.0001). Multivariate analysis revealed that regression of left ventricular mass index significantly correlated with the changes of 8-iso-prostaglandin F(2alpha) (P<0.0001, adjusted R(2)=0.55). Our findings demonstrated for the first time that in addition to its primary hypoglycemia, gliclazide may have an additional effect on reducing left ventricular mass, possibly through attenuation of free radical formation.

Effects of pravastatin on ventricular remodeling by activation of myocardial KATP channels in infarcted rats: role of 70-kDa S6 kinase

Reactive cardiomyocyte hypertrophy after myocardial infarction is an important risk factor for arrhythmias. Myocardial ATP-sensitive potassium (K(ATP)) channels have been implicated in attenuating cardiac hypertrophy by inhibition of 70-kDa S6 kinase. We investigated the effect of pravastatin on ventricular hypertrophy during remodeling after myocardial infarction and whether the attenuated hypertrophic effect was via activation of myocardial K(ATP) channels. Twenty-four hours after ligation of the anterior descending artery, male Wistar rats were randomized to either vehicle, nicorandil (an agonist of K(ATP) channels), pravastatin, glibenclamide (an antagonist of K(ATP) channels), or a combination of nicorandil and glibenclamide or pravastatin and glibenclamide for 4 weeks. Infarct size and mortality were similar among the infarcted groups. Cardiomyocyte sizes isolated by enzymatic dissociation after infarction significantly increased at the border zone in vehicle-treated infarcted rats compared with sham-operated rats. Rats in the nicorandil- and pravastatin-treated groups significantly attenuated cardiomyocyte hypertrophy, as compared with the vehicle-treated group. Arrhythmic scores during programmed stimulation mirrored those of cardiomyocyte hypertrophy. Increased 70-kDa S6 kinase mRNA expression in cardiac remodeling was confirmed by reverse transcription-polymerase chain reaction, consistent with the results of immunohistochemistry and Western blot for the phosphorylation of 70-kDa S6 kinase. Nicorandil-induced effects were abolished by administering glibenclamide. Similarly, the beneficial effects of pravastatin were abolished by administering glibenclamide, implicating K(ATP) channels as the relevant target. Activation of K(ATP) channels by pravastatin administration can attenuate ventricular remodeling through a S6 kinase-dependent pathway after infarction.

Distinct KATP Channels Mediate the Antihypertrophic Effects of Adenosine Receptor Activation in Neonatal Rat Ventricular Myocytes

Recent evidence suggests that both adenosine receptor (AR) and K ATP channel activation exert antihypertrophic effects in cardiac myocytes. We studied the relative contributions of mitochondrial K ATP (mitoK ATP) and sarcolemmal K ATP (sarcK ATP) to the antihypertrophic effects of ARs in primary cultures of neonatal rat ventricular myocytes exposed for 24 h with the alpha1 adrenoceptor agonist phenylephrine (PE). The A1R agonist N6-cyclopentyladenosine (CPA), the A(2A)R agonist CGS21680 [2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine], and the A3R agonist N6-(3-iodobenzyl)adenosine-5'-methyluronamide (IB-MECA) all prevented PE-induced hypertrophy. Glibenclamide, a nonselective K(ATP) channel blocker reversed the antihypertrophic effect of all three AR agonists as determined by cell size and atrial natriuretic peptide expression and early c-fos up-regulation. In contrast, the mitoK(ATP) blocker 5-hydroxydecanoic acid selectively attenuated the effect of CGS21680 and IB-MECA, whereas HMR1098 [1-[[5-[2-(5-chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl]-3-methylthiourea, sodium salt], a specific blocker of sarcK(ATP), only abolished the antihypertrophic effect of CPA. Moreover, both CGS21680 and IB-MECA but not CPA decreased the mitochondrial membrane potential when PE was present, similarly to that seen with diazoxide, and both agents inhibited PE-stimulated elevation in mitochondrial Ca2+. All AR agonists diminished PE-induced phosphoserine/threonine kinase and protein kinase B up-regulation, which was unaffected by any K(ATP) blocker. Our data suggest that AR-mediated antihypertrophic effects are mediated by distinct K(ATP) channels, with sarcK(ATP) mediating the antihypertrophic effects of A1R activation, whereas mitoK(ATP) activation mediates the antihypertrophic effects of both A(2A)R and A3R agonists.

Effects of KR-31378, a novel ATP-sensitive potassium channel activator, on hypertrophy of H9c2 cells and on cardiac dysfunction in rats with congestive heart failure

The present study was performed to evaluate the effects of (2S, 3S, 4R)-N"-cyano-N-(6-amino-3, 4-dihydro-2-dimethoxymethyl-3-hydroxy-2-methyl-2H-1-benzopyran-4yl)-N'-benzylguanidine (KR-31378), a novel mitochondrial ATP-sensitive potassium channel activator, on hypertrophy of H9c2 cells and on cardiac dysfunction in rats with congestive heart failure. In rat heart-derived H9c2 cells treated with hypertrophic agonists, such as angiotensin II, phenylephrine, isoproterenol, and urotensin II, cell size was significantly increased by 27-47%. The increases in cell size induced by the hypertrophic agonists were inhibited by treatment of KR-31378 in a concentration-dependent manner. This was confirmed by the results showing that KR-31378 inhibited the angiotensin II-induced increase in cell protein content. The effect of KR-31378 on the angiotensin II-induced increase in cell size was reversed by mitochondrial ATP-sensitive potassium channel blockers, 5-hydroxydecanoate or glibenclamide. In rats with congestive heart failure, induced by permanent coronary artery occlusion for 8 weeks, KR-31378 significantly reversed the cardiac dysfunction (increase in ratios of stroke volume or cardiac output to body weight) induced by myocardial infarction without reducing infarct size. In addition, KR-31378 significantly inhibited atrial hypertrophy (decrease in ratio of right atrium to body weight) and decreased the serum pro-atrial natriuretic peptide level, a biochemical marker of heart failure. These results suggest that KR-31378 suppresses hypertrophy induced by hypertrophic agonists in H9c2 cells and improves cardiac dysfunction in rats with congestive heart failure induced by myocardial infarction, and that the effects may be mediated by the activation of mitochondrial ATP-sensitive potassium channels.

Nicorandil but not ISDN Upregulates Endothelial Nitric Oxide Synthase Expression, Preventing Left Ventricular Remodeling and Degradation of Cardiac Function in Dahl Salt-sensitive Hypertensive Rats With Congestive Heart Failure

Cardiac endothelial nitric oxide synthase (ecNOS) was suppressed and inducible NOS (iNOS) enhanced at the decompensated heart failure stage in 18-week-old Dahl salt-sensitive (DS) hypertensive rats to which a high-salt diet had been administered from the age of 6 weeks. Nicorandil (NIC) enhanced ecNOS by activating Adenosine triphosphate-sensitive potassium channels (K-ATP channels) in the normal rat left ventricle. In this study, left ventricular hypertrophy, remodeling, function, cardiac ecNOS, and iNOS were compared between NIC and isosorbide dinitrate (ISDN) treatments in DS hypertensive rats with congestive heart failure. We examined DS hypertensive rats of 18 weeks of age to which 8% NaCl had been administered from the age of 6 weeks, and to which subdepressor doses of NIC (6 mg/kg/d), ISDN (6 mg/kg/d), and vehicle (CON) were administered from the age of 11 weeks. Contractility (Ees), stiffness (Eed), left ventricular end-diastolic volume, and left ventricular end-systolic volume were measured by conductance catheter and micromanometer on the basis of the pressure-volume relationship, and mRNA and protein levels of ecNOS and iNOS in the left ventricle were measured by reverse transcription-polymerase chain reaction and Western blot analysis at 18 weeks. LV mass index and LV dimensions were smaller in the NIC and ISDN groups than in the CON group (P < 0.01), and the first parameter was lower in the NIC than in the ISDN group (P < 0.01). Ees was also better maintained in the NIC and ISDN groups than in the CON group (NIC: 3349 +/- 649; ISDN: 2950 +/- 577, P < 0.05 vs. NIC; CON: 1424 +/- 375 mL/mmHg, P < 0.01 vs. treatments). Eed was exacerbated only in the ISDN group. NIC enhanced whereas ISDN suppressed ecNOS mRNA and protein levels (NIC 2.0-fold and 1.8-fold, ISDN 0.70-fold and 0.8-fold vs. CON; P < 0.01, respectively). However, no intragroup differences in iNOS mRNA or protein levels were observed for the 3 groups. More significant improvements in cardiac function and LV hypertrophy regression were observed in an NIC group than in an ISDN group of DS hypertensive rats. Activation of the K-ATP channel seems to induce this beneficial effect, which may be mediated in part by enhanced ecNOS expression in the heart in DS hypertensive congestive heart failure rat model.

Abnormal Glucose Tolerance Contributes to the Progression of Chronic Heart Failure in Patients with Dilated Cardiomyopathy

Since 1) dilated cardiomyopathy (DCM) causes chronic heart failure (CHF), and 2) augmentation of neurohumoral factors such as angiotensin II impairs glucose metabolism, we examined the rate of abnormal glucose metabolism in patients having both DCM and CHF and whether correction of the impairment of glucose metabolism would improve the pathophysiology of CHF in DCM patients. A 75-g oral glucose tolerance test (OGTT) was performed in 56 patients with DCM-induced CHF and 168 age- and sex-matched control subjects. Among the CHF patients, 26.8% and 50.0% suffered from diabetes mellitus (DM) and impaired glucose tolerance (IGT), respectively, showing that abnormal glucose tolerance was more prevalent in DCM patients than in the control subjects (7.7% and 14.3%, respectively). In the patients with DCM-induced CHF, a correlation was observed between the brain natriuretic peptide (BNP) levels and the difference between the plasma glucose levels at the time of fasting and at 2 h of OGTT. Since neither DM nor IGT are thought to cause DCM, the abnormalities of glucose metabolism may be attributed to the progression of CHF. Furthermore, we tested whether correction of the abnormal glucose tolerance using voglibose (an alpha-glucosidase inhibitor) would improve the severity of CHF in another group of 30 patients with DCM-induced CHF and IGT. The patients treated with voglibose for 24 weeks showed decreases in left ventricular dimension, NYHA functional classification values, and plasma BNP levels, and an improvement in cardiac function. In conclusion, abnormal glucose tolerance was more prevalent among patients with DCM-induced CHF than controls, and the correction of IGT improved the pathophysiology of CHF.

Continuous Administration of Nicorandil Decreases QT Dispersion During the Chronic Phase of Acute Myocardial Infarction

We previously reported that continuous intravenous (IV) administration of nicorandil (NIC) inhibits QT dispersion (QTd). However, no prior study has evaluated the efficacy of NIC when administered orally to acute myocardial infarction (AMI) patients following continuous IV administration. Thirty patients with anteroseptal infarction in whom revascularization was performed successfully within 6 hours of AMI onset were included in the study and assigned to one of 3 groups: group A (continuous IV administration of NIC), group B (continuous IV and oral administration of NIC), and group C (no treatment with NIC). After 24 hours, QTd in groups A and B was significantly decreased compared to QTd in group C (P < 0.01) (group A, 58.1; group B, 58.2; and group C, 81.3). The QTd obtained 3 months later was significantly shorter in group B subjects who were orally administered NIC, and QTd before percutaneous coronary intervention (PCI) was restored in group A, in which no NIC had been administered orally [group A, 66.7; group B, 54.1; and group C, 73.9; P < 0.05 (group A versus group B) and P < 0.01 (group B versus group C)]. The effects were evaluated by comparing different routes of administration. Continuous IV and subsequent oral administration of NIC inhibited prolongation of QTd, suggesting that these effects may prevent the occurrence of cardiac events during both the acute and chronic phases of AMI.

Effects of Nicorandil on Monocrotaline-Induced Pulmonary Arterial Hypertension in Rats

We investigated whether nicorandil might prevent and reverse monocrotaline (MCT)-induced pulmonary arterial hypertension. Rats were injected with 50 mg/kg of MCT subcutaneously and randomized to either 7.5 mg/kg/d of nicorandil in drinking water or placebo for 3 weeks. Animals that were treated with MCT and survived for 3 weeks were assigned to either nicorandil or placebo. Nicorandil markedly attenuated pulmonary arterial hypertension with severe structural remodeling of the pulmonary vessels. The survival rate at 3 weeks after treatment was significantly increased in the nicorandil group compared with the placebo group (73% versus 39%, P<0.05). In the placebo group, endothelial nitric oxide synthase (eNOS) protein was significantly decreased, the numbers of the CD45-positive cells and those of the proliferating cell nuclear antigen-positive cells were increased in the lung tissue, and P-selectin was intensely expressed on the endothelium of the pulmonary arteries. These features were prevented by nicorandil. Late treatment with nicorandil did not palliate established pulmonary arterial hypertension nor improved survival. Thus, nicorandil inhibited development of MCT-induced pulmonary arterial hypertension but failed to reverse it. These effects were associated with marked up-regulation of diminished lung eNOS protein along with improvement of pulmonary vascular endothelial activation and anti-inflammatory and anti-proliferative effects in the lung tissue.

Upregulation of adrenomedullin and its receptor components during cardiomyocyte hypertrophy induced by chronic inhibition of nitric oxide synthesis in rats

Adrenomedullin may provide a compensatory mechanism to attenuate left ventricular hypertrophy (LVH). Nitric oxide synthase inhibition, induced by chronic administration of N(omega)-nitro-L-arginine methyl ester (L-NAME) to rats, induces cardiac hypertrophy in some, but not all cases; there are few reports of direct assessment of cardiomyocyte parameters. The objective was to characterize hypertrophic parameters in left (LV) and right ventricular (RV) cardiomyocytes after administration of L-NAME to rats for 8 wk and to determine whether adrenomedullin and its receptor components were upregulated. After treatment with L-NAME (20 and 50 mg x kg(-1) x day(-1)), compared with nontreated animals, 1) systolic blood pressure increased (by 34.2 and 104.9 mmHg), 2) heart weight-to-body wt ratio increased 24.1% at the higher dose (P < 0.05), 3) cardiomyocyte protein mass increased (P = NS), 4) cardiomyocyte protein synthesis ([14C]phenylalanine incorporation) increased (P < 0.05), 5) expression of skeletal alpha-actin, atrial natriuretic peptide, brain natriuretic peptide, and ET-1 mRNAs was enhanced (P < 0.05) in LV but not RV cardiomyocytes at 20 and 50 mg x kg(-1) x day(-1), respectively, and 6) expression of adrenomedullin, receptor activity-modifying protein 3 (RAMP3), and RAMP2 (but not calcitonin receptor-like receptor and RAMP1) mRNAs was increased by L-NAME (20 mg x kg(-1) x day(-1)) in LV. In conclusion, L-NAME enhanced protein synthesis in both LV and RV cardiomyocytes but elicited a hypertrophic phenotype accompanied by altered expression of the counterregulatory peptide adrenomedullin and receptor components (RAMP2, RAMP3) in LV only, indicating that the former is due to impaired nitric oxide synthesis, whereas the phenotypic changes are due to pressure overload.

Long-Term Oral Treatment with Nicorandil Prevents the Progression of Left Ventricular Hypertrophy and Preserves Viability

Left ventricular (LV) hypertrophy and myocardial infarction play important roles in the progressive LV dysfunction. We hypothesized that the potassium-channel opener and nitrate-like vasodilator nicorandil prevents the development of LV hypertrophy and preserves myocardial viability. Twenty-four rats were subjected to aortic stenosis for 8 weeks to produce LV hypertrophy and assigned to non-treated and nicorandil-treated (3 mg/kg/d) groups. A third group (n = 12) without stenosis or treatment served as control. All 36 animals were subjected to reperfused infarction by 25-minute occlusion of the left coronary artery followed by 3 hours of reperfusion. Spin-echo magnetic resonance (MR) images were acquired to measure infarction size, LV mass, volumes, ejection fraction, and wall thickness. A necrosis-specific contrast agent, Gadophrin-3, was used to delineate necrotic myocardium. Aortic and LV pressures were measured invasively. At postmortem, LV mass and infarction size were determined and compared with MR findings. Nicorandil prevented the development of LV hypertrophy. Infarction size of nicorandil-treated animals was similar to control animals. Non-treated animals with aortic banding had higher LV mass (P < 0.001), lower ejection fraction (P = 0.006), and larger infarction size (P < 0.001) than treated and control animals. MR and postmortem data showed close agreement. Nicorandil therapy prevented the development of cardiac hypertrophy and protected myocardium against ischemia.

Effect of pravastatin on left ventricular mass by activation of myocardial K ATP channels in hypercholesterolemic rabbits

Epidemiological studies showed that hypercholesterolemia was associated with a higher left ventricular mass. Myocardial ATP-sensitive potassium (K(ATP)) channels have been implicated in the development of cardiac hypertrophy. We investigated the effect of pravastatin on hypercholesterolemia-induced ventricular hypertrophy and whether the attenuated hypertrophic effect was via activation of myocardial K(ATP) channels. In this study, we evaluated the hemodynamic, biochemical, and morphological responses to pravastatin in cholesterol-fed (1%) rabbits. Male New Zealand White rabbits were randomized to either vehicle, nicorandil (an agonist of K(ATP) channels), pravastatin, glibenclamide (an antagonist of K(ATP) channels), or a combination of nicorandil and glibenclamide or pravastatin and glibenclamide for 8 weeks. The left ventricular weight and left ventricular myocyte sizes increased 8 weeks after cholesterol-feeding in comparison to that in normocholesterolemic rabbits. Pravastatin administration significantly decreased the left ventricular weight by 12% and cardiomyocyte cell areas by 30%. Hyperlipidemic rabbits in the nicorandil- and pravastatin-treated groups significantly attenuated cardiomyocyte hypertrophy, as compared with the vehicle-treated group (3162 +/- 277 microm(2), 3372 +/- 228 microm(2) versus 4388 +/- 163 microm(2) in the vehicle group, both P < 0.0001, respectively). Nicorandil-induced effects were abolished by administering glibenclamide. Similarly, pravastatin-induced beneficial effects were reversed by the addition of glibenclamide, implicating K(ATP) channels as the relevant target. The results of the present study suggest a pathogenetic role of K(ATP) channels in hypercholesterolemia-induced ventricular hypertrophy. The antihypertropic effects of pravastatin may be related to activation of K(ATP) channels, and result in an amelioration of cardiomyocyte hypertrophy development by an atherogenic diet.

Accentuation of high susceptibility of hypertrophied myocardium to ischemia: Complementary assessment of Gadophrin-enhancement and left ventricular function with MRI

The aim of the study was to compare infarction size and left ventricular (LV) function in normal and hypertrophied hearts after brief ischemia using Gadophrin-enhancement and functional assessment by MRI. Rats (n = 20) were assigned to aortic banding to induce LV hypertrophy or control. Eight weeks later, rats were subjected to 25 min of regional myocardial ischemia followed by 3 hr of reperfusion. The necrosis-specific agent Gadophrin-3 was injected to delineate infarcted myocardium on MRI. Effects of aortic banding and ischemia on LV mass and function were determined. At postmortem, areas at risk and infarction were measured. Close correlation was found between LV mass measured with MRI and at postmortem (r = 0.98). LV mass measured with MRI was significantly greater (0.81 +/- 0.02 g) in animals with aortic banding compared to control (0.62 +/- 0.02 g; P < 0.001). Infarction size was larger in hypertrophied hearts (19.0 +/- 1.4% / 18.3 +/- 1.5%) than in control (9.8 +/- 1.7% / 9.2 +/- 2.0%) on Gadophrin-enhanced MRI and at postmortem, respectively. Similarly, greater impairment in ejection fraction was observed in hypertrophied hearts with MRI (39 +/- 4% vs. 49 +/- 2%; P = 0.02). Gadophrin-3 provides accurate estimation of infarct size in hypertrophied hearts. Hypertrophied hearts are more sensitive to ischemia than nonhypertrophied hearts. The complementary assessment of Gadophrin-enhancement and LV function with MRI provides unique information about myocardium sensitivity to ischemia.

Long-acting Ca2+ blockers prevent myocardial remodeling induced by chronic NO inhibition in rats

Chronic inhibition of nitric oxide (NO) synthesis induces cardiac remodeling independent of systemic hemodynamic changes in rats. We examined whether long-acting dihydropyridine calcium channel blockers block myocardial remodeling and whether the activation of 70-kDa S6 kinase (p70S6K) and extracellular signal-regulated kinase (ERK) are involved. Ten groups of Wistar-Kyoto rats underwent 8 weeks of drug treatment consisting of a combination of NO synthase inhibitor NG-nitro-l-arginine methyl ester (L-NAME), an inactive isomer (D-NAME), amlodipine (1 or 3 mg/kg per day), or benidipine (3 or 10 mg/kg per day). In other groups, L-NAME was also used in combination with a p70S6K inhibitor (rapamycin), a MEK inhibitor (PD98059), and hydralazine. Systolic blood pressure (SBP), heart rate, and left ventricular weight (LVW) were measured, together with histological examinations and kinase assay. L-NAME increased SBP and LVW (1048+/-22 versus 780+/-18 mg, P<0.01) compared with the control, showing a significant increase in cross-sectional area of cardiomyocytes after 8 weeks. Amlodipine, benidipine, or hydralazine equally attenuated the increase in SBP induced by L-NAME. However, both amlodipine and benidipine but not hydralazine attenuated the increase in LVW by L-NAME (789+/-27, 825+/-20 mg, P<0.01, and 1118+/-29 mg, NS, respectively), also confirmed by histological analysis. L-NAME caused a 2.2-fold/1.8-fold increase in p70S6K/ERK activity in myocardium compared with the control, both of which were attenuated by both amlodipine and benidipine but not hydralazine. Both rapamycin and PD98059 attenuated cardiac hypertrophy in this model. Thus, long-acting dihydropyridine calcium channel blockers inhibited cardiac hypertrophy induced by chronic inhibition of NO synthesis by inhibiting both p70S6K and ERK in vivo.