Masayuki Shimano

Pioglitazone, a peroxisome proliferator-activated receptor-gamma activator, attenuates atrial fibrosis and atrial fibrillation promotion in rabbits with congestive heart failure

BACKGROUND The peroxisome proliferator-activated receptor-gamma (PPAR-gamma) activator pioglitazone antagonizes angiotensin II actions and possesses anti-inflammatory and antioxidant properties in vitro. There is evidence that pioglitazone improves ventricular remodeling in some experimental models. OBJECTIVE The purpose of this study was to assess the effects of pioglitazone on arrhythmogenic atrial structural remodeling versus the effects of the angiotensin II type 1 receptor blocker candesartan in a rabbit model of congestive heart failure. METHODS Rabbits subjected to ventricular tachypacing at 380 to 400 bpm for 4 weeks in the absence and presence of treatment with pioglitazone, candesartan, and combined pioglitazone and candesartan were assessed by electrophysiologic study, atrial fibrosis measurements, and cytokine expression analyses. RESULTS Atrial fibrillation (AF) lasting longer than 2 seconds was induced in no nonpaced controls but in all ventricular tachypacing-only rabbits (mean duration of AF: 8.0 +/- 1.4 seconds). Pioglitazone reduced the duration of AF (3.5 +/- 0.2 seconds, P <.05) and attenuated atrial structural remodeling, with significant reductions in interatrial activation time (50 +/- 2 ms vs 41 +/- 2 ms, P <.05) and atrial fibrosis (16.8% +/- 0.8% vs 10.9% +/- 0.7%, P <.05; control 1.6% +/- 0.2%), effects comparable to those of candesartan (duration of AF: 3.0 +/- 0.2 seconds; activation time 44 +/- 2 ms; fibrosis: 9.4% +/- 0.6%). Both pioglitazone and candesartan reduced transforming growth factor-beta1, tumor necrosis factor-alpha, and activated extracellular signal-regulated kinase expression similarly, but neither affected p38-kinase or c-Jun N-terminal kinase activation. The effects of combined pioglitazone and candesartan therapy were not significantly different from the effects of pioglitazone or candesartan alone. CONCLUSION Pioglitazone can attenuate congestive heart failure-induced atrial structural remodeling and AF promotion, with effects similar to those of candesartan. PPAR-gamma may be a potential therapeutic target for human AF.

Caloric Restriction Stimulates Revascularization in Response to Ischemia via Adiponectin-mediated Activation of Endothelial Nitric-oxide Synthase

Caloric restriction (CR) can extend longevity and modulate the features of obesity-related metabolic and vascular diseases. However, the functional roles of CR in regulation of revascularization in response to ischemia have not been examined. Here we investigated whether CR modulates vascular response by employing a murine hindlimb ischemia model. Wild-type (WT) mice were randomly divided into two groups that were fed either ad libitum (AL) or CR (65% of the diet consumption of AL). Four weeks later, mice were subjected to unilateral hindlimb ischemic surgery. Body weight of WT mice fed CR (CR-WT) was decreased by 26% compared with WT mice fed AL (AL-WT). Revascularization of ischemic hindlimb relative to the contralateral limb was accelerated in CR-WT compared with AL-WT as evaluated by laser Doppler blood flow and capillary density analyses. CR-WT mice had significantly higher plasma levels of the fat-derived hormone adiponectin compared with AL-WT mice. In contrast to WT mice, CR did not affect the revascularization of ischemic limbs of adiponectin-deficient (APN-KO) mice. CR stimulated the phosphorylation of endothelial nitric-oxide synthase (eNOS) in the ischemic limbs of WT mice. CR increased plasma adiponectin levels in eNOS-KO mice but did not stimulate limb perfusion in this strain. CR-WT mice showed enhanced phosphorylation of AMP-activated protein kinase (AMPK) in ischemic muscle, and administration of AMPK inhibitor compound C abolished CR-induced increase in limb perfusion and eNOS phosphorylation in WT mice. Our observations indicate that CR can promote revascularization in response to tissue ischemia via an AMPK-eNOS-dependent mechanism that is mediated by adiponectin.

Adiponectin deficiency exacerbates cardiac dysfunction following pressure overload through disruption of an AMPK-dependent angiogenic response

Although increasing evidence indicates that an adipokine adiponectin exerts protective actions on heart, its effects on coronary angiogenesis following pressure overload have not been examined previously. Because disruption of angiogenesis during heart growth leads to contractile dysfunction and heart failure, we hypothesized that adiponectin modulates cardiac remodeling in response to pressure overload through its ability to regulate adaptive angiogenesis. Adiponectin-knockout (APN-KO) and wild-type (WT) mice were subjected to pressure overload caused by transverse aortic constriction (TAC). APN-KO mice exhibited greater cardiac hypertrophy, pulmonary congestion, left ventricular (LV) interstitial fibrosis and LV systolic dysfunction after TAC surgery compared with WT mice. APN-KO mice also displayed reduced capillary density in the myocardium after TAC, which was accompanied by a significant decrease in expression of vascular endothelial growth factor (VEGF) and phosphorylation of AMP-activated protein kinase (AMPK). Inhibition of AMPK in WT mice resulted in aggravated LV systolic function, attenuated myocardial capillary density and decreased VEGF expression in response to TAC. The adverse effects of AMPK inhibition on cardiac function and angiogenic response following TAC were diminished in APN-KO mice relative to WT mice. Moreover, adenovirus-mediated VEGF delivery reversed the TAC-induced deficiencies in cardiac microvessel formation and ventricular function observed in the APN-KO mice. In cultured cardiac myocytes, adiponectin treatment stimulated VEGF production, which was inhibited by inactivation of AMPK signaling pathway. Collectively, these data show that adiponectin deficiency can accelerate the transition from cardiac hypertrophy to heart failure during pressure overload through disruption of AMPK-dependent angiogenic regulatory axis.

Adiponectin promotes endothelial progenitor cell number and function

Obesity‐linked diseases are associated with suppressed endothelial progenitor cell (EPC) function. Adiponectin is an adipose‐derived protein that is downregulated in obese and diabetic subjects. Here, we investigated the effects of adiponectin on EPCs. EPC levels did not increase in adiponectin deficient (APN‐KO) in response to hindlimb ischemia. Adenovirus‐mediated delivery of adiponectin increased EPC levels in both WT and APN‐KO mice. Incubation of human peripheral blood mononuclear cells with adiponectin led to an increase of the number of EPCs. Adiponectin induced EPC differentiation into network structures and served as a chemoattractant in EPC migration assays. These data suggest that hypoadiponectinemia may contribute to the depression of EPC levels that are observed in patients with obesity‐related cardiovascular disorders.

Impact of a Single Intracoronary Administration of Adiponectin on Myocardial Ischemia/Reperfusion Injury in a Pig Model

Background—Adiponectin plays a protective role in the development of obesity-linked disorders. We demonstrated that adiponectin exerts beneficial actions on acute ischemic injury in mice hearts. However, the effects of adiponectin treatment in large animals and its feasibility in clinical practice have not been investigated. This study investigated the effects of intracoronary administration of adiponectin on myocardial ischemia-reperfusion (I/R) injury in pigs. Methods and Results—The left anterior descending coronary artery was occluded in pigs for 45 minutes and then reperfused for 24 hours. Recombinant adiponectin protein was given as a bolus intracoronary injection during ischemia. Cardiac functional parameters were measured by a manometer-tipped catheter. Apoptosis was evaluated by terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling staining. Tumor necrosis factor-α and interleukin-10 transcripts were analyzed by real-time polymerase chain reaction. Serum levels of derivatives of reactive oxygen metabolites and biological antioxidant potential were measured. Adiponectin protein was determined by immunohistochemical and Western blot analyses. Intracoronary administration of adiponectin protein led to a reduction in myocardial infarct size and improvement of left ventricular function in pigs after I/R. Injected adiponectin protein accumulated in the I/R-injured heart. Adiponectin treatment resulted in decreased tumor necrosis factor-α and increased interleukin-10 mRNA levels in the myocardium after I/R. Adiponectin-treated pigs had reduced apoptotic activity in the I/R-injured heart and showed increased biological antioxidant potential levels and decreased derivatives of reactive oxygen metabolite levels in the blood stream after I/R. Conclusions—These data suggest that adiponectin protects against I/R injury in a preclinical pig model through its ability to suppress inflammation, apoptosis, and oxidative stress. Administration of intracoronary adiponectin could be a useful adjunctive therapy for acute myocardial infarction.

Cardiac myocyte follistatin-like 1 functions to attenuate hypertrophy following pressure overload

Factors secreted by the heart, referred to as “cardiokines,” have diverse actions in the maintenance of cardiac homeostasis and remodeling. Follistatin-like 1 (Fstl1) is a secreted glycoprotein expressed in the adult heart and is induced in response to injurious conditions that promote myocardial hypertrophy and heart failure. The aim of this study was to investigate the role of cardiac Fstl1 in the remodeling response to pressure overload. Cardiac myocyte-specific Fstl1-KO mice were constructed and subjected to pressure overload induced by transverse aortic constriction (TAC). Although Fstl1-KO mice displayed no detectable baseline phenotype, TAC led to enhanced cardiac hypertrophic growth and a pronounced loss in ventricular performance by 4 wk compared with control mice. Conversely, mice that acutely or chronically overexpressed Fstl1 were resistant to pressure overload-induced hypertrophy and cardiac failure. Fstl1-deficient mice displayed a reduction in TAC-induced AMP-activated protein kinase (AMPK) activation in heart, whereas Fstl1 overexpression led to increased myocardial AMPK activation under these conditions. In cultured neonatal cardiomyocytes, administration of Fstl1 promoted AMPK activation and antagonized phenylephrine-induced hypertrophy. Inhibition of AMPK attenuated the antihypertrophic effect of Fstl1 treatment. These results document that cardiac Fstl1 functions as an autocrine/paracrine regulatory factor that antagonizes myocyte hypertrophic growth and the loss of ventricular performance in response to pressure overload, possibly through a mechanism involving the activation of the AMPK signaling axis.

Cardiokines Recent Progress in Elucidating the Cardiac Secretome

The sets of proteins secreted from cells, ie, secretomes, play crucial roles in intercellular and intertissue communication during tissue development and growth and in response to various pathological stresses. The secretomes produced by the heart encompass a group of proteins that have been referred to as cardiokines. In todays era of molecular sophistication, the number of identified cardiokine candidates is steadily increasing as a result of the desire to identify new biomarkers and targets for cardiovascular disease treatment. It is widely recognized that the cells of the heart, including myocytes, fibroblasts, vascular cells, and progenitor cells, secrete various subsets of regulatory proteins in response to changes in the cardiac environment.1–5 These secreted proteins are required for the maintenance of normal cardiac function, and they control pathological remodeling of the myocardium in response to injury through their ability to modulate myocyte death, fibroblast activation, inflammation, and vascular growth and regression. In addition, some of these factors function systematically, influencing kidney function or cachectic processes. Examples of well-known cardiokines include atrial natriuretic peptide and brain natriuretic peptide, which are synthesized mainly in the myocardium and upregulated in response to myocardial stretching.6,7 Both atrial natriuretic peptide and brain natriuretic peptide exert beneficial actions on cardiac remodeling by directly affecting cardiac cells in an autocrine and/or paracrine manner. In addition, atrial natriuretic peptide and brain natriuretic peptide influence electrolyte and water excretion in the kidney and regulate vascular tone and vascular cell growth via endocrine mechanisms.7 Cardiac cells produce tumor necrosis factor-α and transforming growth factor-β1 in pathological states, and these factors can promote pathological myocardial remodeling by promoting the recruitment of inflammatory cells or by facilitating hypertrophic growth and fibrosis.8,9 Under conditions of stress, the heart also produces angiotensin II, contributing to cardiac …

Reactive oxidative metabolites are associated with atrial conduction disturbance in patients with atrial fibrillation

BACKGROUND Oxidative stress is associated with atrial fibrillation (AF). However, little is known about the relationship between serum markers of oxidation and electrical activity in patients with AF. OBJECTIVE The purpose of this study was to investigate the possible association between serum markers of reactive oxidative metabolism and atrial remodeling in paroxysmal and persistent AF. METHODS Derivatives of reactive oxidative metabolites (DROM), an index of oxidative stress, were measured in 306 consecutive patients with AF (225 paroxysmal, 81 persistent) undergoing radiofrequency (RF) catheter ablation. Filtered P-wave duration by P-wave signal-averaged ECG and levels of high-sensitivity C-reactive protein (CRP) as an inflammatory marker also were measured. RESULTS Patients were followed up for 1.2 +/- 0.8 years. DROM levels in patients with persistent AF were significantly higher than in patients with paroxysmal AF (341.6 +/- 85.5 Carratelli [Carr] units vs 305.0 +/- 77.7 Carr units, P <.001). DROM levels showed a tighter, positive correlation with filtered P-wave duration in persistent AF patients (r = 0.56, P <.001) than in all AF patients (r = 0.13, P <.05). DROM levels also showed a weaker but significant correlation with high-sensitivity CRP in patients with AF. Kaplan-Meier analysis revealed that the highest quartile of basal DROM levels exhibited a significantly higher AF recurrence rate after RF catheter ablation in patients with paroxysmal AF (P <.01). CONCLUSION Serum markers of oxidative stress reflect atrial conduction disturbance and predict AF recurrence after RF catheter ablation in paroxysmal AF patients. DROM could serve as a biomarker for predicting risk of AF recurrence after RF catheter ablation.

Eicosapentaenoic acid prevents atrial fibrillation associated with heart failure in a rabbit model

Atrial fibrillation (AF) is associated with morbidity and mortality of heart failure. Eicosapentaenoic acid (EPA), which is contained in fish oil, was shown to reduce the risk of cardiovascular diseases. We investigated the effects of EPA on AF associated with heart failure in a rabbit model. Rabbits were subjected to ventricular tachypacing (VTP) for 4 wk with or without EPA treatment. Continuous VTP induced heart failure status in these rabbits. The duration of AF (DAF) induced by burst pacing was analyzed by electrophysiological studies. VTP resulted in increased DAF following burst pacing. EPA treatment attenuated increased DAF. Atrial fibrosis increased in response to VTP, accompanied by extracellular signal-regulated kinase (ERK) phosphorylation and transforming growth factor-β1 (TGF-β1) expression in the atrium. Treatment with EPA attenuated atrial fibrosis, ERK phosphorylation, and TGF-β1 expression in response to VTP. EPA treatment increased adiponectin as an anti-inflammatory adipokine and decreased tumor necrosis factor-α as a proinflammatory adipokine in the atrium and epicardial adipose tissues. EPA attenuated VTP-induced AF promotion and atrial remodeling, which was accompanied by modulating the profiles of adipokine production from epicardial adipose tissue. EPA may be useful for prevention and treatment of AF associated with heart failure.

Adiponectin Modulates Oxidative Stress-Induced Autophagy in Cardiomyocytes

Diastolic heart failure (HF) i.e., “HF with preserved ejection fraction” (HF-preserved EF) accounts for up to 50% of all HF presentations; however there have been no therapeutic advances. This stems in part from an incomplete understanding about HF-preserved EF. Hypertension is the major cause of HF-preserved EF whilst HF-preserved EF is also highly associated with obesity. Similarly, excessive reactive oxygen species (ROS), i.e., oxidative stress occurs in hypertension and obesity, sensitizing the heart to the renin-angiotensin-aldosterone system, inducing autophagic type-II programmed cell death and accelerating the propensity to adverse cardiac remodeling, diastolic dysfunction and HF. Adiponectin (APN), an adipokine, mediates cardioprotective actions but it is unknown if APN modulates cardiomyocyte autophagy. We tested the hypothesis that APN ameliorates oxidative stress-induced autophagy in cardiomyocytes. Isolated adult rat ventricular myocytes were pretreated with recombinant APN (30µg/mL) followed by 1mM hydrogen peroxide (H2O2) exposure. Wild type (WT) and APN-deficient (APN-KO) mice were infused with angiotensin (Ang)-II (3.2mg/kg/d) for 14 days to induced oxidative stress. Autophagy-related proteins, mTOR, AMPK and ERK expression were measured. H2O2 induced LC3I to LC3II conversion by a factor of 3.4±1.0 which was abrogated by pre-treatment with APN by 44.5±10%. However, neither H2O2 nor APN affected ATG5, ATG7, or Beclin-1 expression. H2O2 increased phospho-AMPK by 49±6.0%, whilst pretreatment with APN decreased phospho-AMPK by 26±4%. H2O2 decreased phospho-mTOR by 36±13%, which was restored by APN. ERK inhibition demonstrated that the ERK-mTOR pathway is involved in H2O2-induced autophagy. Chronic Ang-II infusion significantly increased myocardial LC3II/I protein expression ratio in APN-KO vs. WT mice. These data suggest that excessive ROS caused cardiomyocyte autophagy which was ameliorated by APN by inhibiting an H2O2-induced AMPK/mTOR/ERK-dependent mechanism. These findings demonstrate the anti-oxidant potential of APN in oxidative stress-associated cardiovascular diseases, such as hypertension-induced HF-preserved EF.