Cardiomyocyte Functional Etiology in Heart Failure With Preserved Ejection Fraction Is Distinctive-A New Preclinical Model.

BACKGROUND: Among the growing numbers of patients with heart failure, up to one half have heart failure with preserved ejection fraction (HFpEF). The lack of effective treatments for HFpEF is a substantial and escalating unmet clinical need-and the lack of HFpEF-specific animal models represents a major preclinical barrier in advancing understanding of HFpEF. As established treatments for heart failure with reduced ejection fraction (HFrEF) have proven ineffective for HFpEF, the contention that the intrinsic cardiomyocyte phenotype is distinct in these 2 conditions requires consideration. Our goal was to validate and characterize a new rodent model of HFpEF, undertaking longitudinal investigations to delineate the associated cardiac and cardiomyocyte pathophysiology. METHODS AND RESULTS: The selectively inbred Hypertrophic Heart Rat (HHR) strain exhibits adult cardiac enlargement (without hypertension) and premature death (40% mortality at 50 weeks) compared to its control strain, the normal heart rat. Hypertrophy was characterized in vivo by maintained systolic parameters (ejection fraction at 85%-90% control) with marked diastolic dysfunction (increased E/E'). Surprisingly, HHR cardiomyocytes were hypercontractile, exhibiting high Ca2+ operational levels and markedly increased L-type Ca2+ channel current. In HHR, prominent regions of reparative fibrosis in the left ventricle free wall adjacent to the interventricular septum were observed. CONCLUSIONS: Thus, the cardiomyocyte remodeling process in the etiology of this HFpEF model contrasts dramatically with the suppressed Ca2+ cycling state that typifies heart failure with reduced ejection fraction. These findings may explain clinical observations, that treatments considered appropriate for heart failure with reduced ejection fraction are of little benefit for HFpEF-and suggest a basis for new therapeutic strategies.

A Small Cohort Omega-3 PUFA Supplement Study: Implications of Stratifying According to Lipid Membrane Incorporation in Cardiac Surgical Patients.

BACKGROUND: Epidemiological studies and randomised clinical trials (RCTs) report disparate findings in relation to omega-3 polyunsaturated fatty acids (n-3 PUFA) benefit for cardiac patients. With RCTs interpretation is potentially confounded by background n-3 PUFA intake. The goal of this pilot, small cohort, pre-surgical supplementation study was to evaluate postoperative atrial fibrillation (AF) and cardiac molecular expression profiles employing two data analysis approaches - by treatment randomisation and by stratification using measured n-3 PUFA. METHODS: Patients (n=20) received 3g/day of fish or placebo oil (FO vs PO) in a double blind randomised protocol prior to elective coronary artery graft and valve surgery. Groups were matched for age, gender, and mean treatment duration (∼20 days). Resected atrial myocardium was sampled for assay of viability metabolic markers, and blood obtained for erythrocyte membrane lipid measurement. RESULTS: There was substantial overlap of cell membrane n-3 PUFA content across PO and FO groups, and no group treatment effects on AF incidence or myocardial molecular marker levels were detected. In contrast, data stratification using membrane n-3 PUFA content (at 8% total membrane lipid) achieved significant separation of patients (by n-6:n-3 PUFA ratio), a significant differential cardiac expression of the marker peroxisomal proliferator-activated receptor, but no difference in AF incidence. CONCLUSIONS: This small n-3 PUFA case study demonstrates that the same cohort may yield differing findings when evaluated using randomisation or stratification approaches based on direct molecular measures in cell membranes.

Dietary omega-6 fatty acid replacement selectively impairs cardiac functional recovery after ischemia in female (but not male) rats.

A definitive understanding of the role of dietary lipids in determining cardioprotection (or cardiodetriment) has been elusive. Randomized trial findings have been variable and sex specificity of dietary interventions has not been determined. In this investigation the sex-selective cardiac functional effects of three diets enriched by omega-3 or omega-6 polyunsaturated fatty acids (PUFA) or enriched to an equivalent extent in saturated fatty acid components were examined in rats after an 8-wk treatment period. In females the myocardial membrane omega-6:omega-3 PUFA ratio was twofold higher than males in the omega-6 diet replacement group. In diets specified to be high in omega-3 PUFA or in saturated fat, this sex difference was not apparent. Isolated cardiomyocyte and heart Langendorff perfusion experiments were performed, and molecular measures of cell viability were assessed. Under basal conditions the contractile performance of omega-6 fed female cardiomyocytes and hearts was reduced compared with males. Omega-6 fed females exhibited impaired systolic resilience after ischemic insult. This response was associated with increased postischemia necrotic cell damage evaluated by coronary lactate dehydrogenase during reperfusion in omega-6 fed females. Cardiac and myocyte functional parameters were not different between omega-3 and saturated fat dietary groups and within these groups there were no discernible sex differences. Our data provide evidence at both the cardiac and cardiomyocyte levels that dietary saturated fatty acid intake replacement with an omega-6 (but not omega-3) enriched diet has selective adverse cardiac effect in females. This finding has potential relevance in relation to women, cardiac risk, and dietary management.

Ca2+/calmodulin-dependent protein kinase inhibition suppresses post-ischemic arrhythmogenesis and mediates sinus bradycardic recovery in reperfusion.

BACKGROUND: Ca(2+)/calmodulin-dependent protein kinase (CaMKII) activation is known to be associated with conditions where the incidence of arrhythmias is increased, and where cardiomyocyte Ca(2+)-overload occurs. The goal of this study was to determine whether CaMKII inhibition in the intact heart may be linked to the suppression of ventricular arrhythmias occurring during reperfusion after an ischemic insult. METHODS: Non-paced male rat hearts (n = 8-11) were treated with a CaMKII inhibitor (KN93, 2.5 µmol/L) 10 min prior to global ischemia (20 min) and for the initial 10 min of reperfusion. Cardiac mechanical and arrhythmic responses were evaluated under constant pressure perfusion conditions and myocyte damage assessed by measurement of coronary effluent lactate dehydrogenase (LDH). RESULTS: Under basal conditions, KN93 increased coronary flow (41 ± 8% increase, p<0.05) and was negatively inotropic (29 ± 7% decrease, p<0.05), but did not affect heart rate. Ischemic contracture was significantly diminished in KN93-treated hearts (onset, min: 11.48 ± 0.50 vs 16.27 ± 1.23, p<0.05). CaMKII inhibition in early reperfusion almost completely abolished the incidence of ventricular tachycardia/fibrillation in reperfusion (11/11 control vs 1/8 KN93). In the absence of ventricular arrhythmias, heart rate was substantially reduced (% basal; 100 ± 3% vs 46 ± 8%, p<0.05) throughout reperfusion. Left ventricular developed pressure was initially low in KN93 hearts post-ischemia, but recovered to control levels by the end of 60 min reperfusion (68 ± 5% vs 56 ± 5%, p = ns). LDH was significantly reduced in KN93-treated hearts. CONCLUSION: Although CaMKII inhibition diminishes contractile performance of the intact heart in the initial post-ischemic period, it provides crucial benefits through protection against potentially lethal reperfusion-induced arrhythmias and cardiomyocyte sarcolemmal rupture.

Aromatase deficiency confers paradoxical postischemic cardioprotection.

The conventional view is that estrogen confers female cardioprotection. Estrogen synthesis depends on androgen availability, with aromatase regulating conversion of testosterone to estradiol. Extragonadal aromatase expression mediates estrogen production in some tissues, but a role for local steroid conversion has not yet been demonstrated in the heart. This study's goal was to investigate how aromatase deficiency influences myocardial function and ischemic resilience. RT-PCR analysis of C57Bl/6 mouse hearts confirmed cardiac-specific aromatase expression in adult females. Functional performance of isolated hearts from female aromatase knockout (ArKO) and aromatase wild-type mice were compared. Left ventricular developed pressures were similar in aerobic perfusion, but the maximal rate of rise of ventricular pressure was modestly reduced in ArKO hearts (3725 ± 144 vs. 4272 ± 154 mm Hg/sec, P < 0.05). After 25 min of ischemia, the recovery of left ventricular developed pressure was substantially improved in ArKO (percentage of basal at 60 min of reperfusion, 62 ± 8 vs. 30 ± 6%; P < 0.05). Hypercontracture was attenuated (end diastolic pressure, 25 ± 5 vs. 51 ± 1 mm Hg; P < 0.05), and lactate dehydrogenase content of coronary effluent was reduced throughout reperfusion in ArKO hearts. This was associated with a hyperphosphorylation of phospholamban and a reduction in phosphorylated Akt. Immediately after reperfusion, ArKO hearts exhibited increased incidence of ventricular premature beats (194 ± 70 vs. 46 ± 6, P < 0.05). These observations indicate more robust functional recovery, reduced cellular injury, and modified cardiomyocyte Ca(2+) handling in aromatase-deficient hearts. Our findings indicate that androgen-to-estrogen conversion may be of pathophysiologic importance to the heart and challenge the notion that estrogen deficiency is deleterious. These studies suggest the possibility that aromatase suppression may offer inotropic benefit in the acute ischemia/reperfusion setting with appropriate arrhythmia management.

Evaluating RNA preparation options for archived myocardial biopsies.

High quality RNA is the key to producing meaningful gene expression analyses. Human cardiac tissue specimens are extremely valuable, but may not always be obtained under optimal conditions and are frequently fibrotic. We provide a practical guide to assist in assessing the efficacy of two different RNA extraction methods applied to these challenging specimens. We describe how to compare 'single-step' and 'multi-step' extraction processes and discuss how to interpret information available through microfluidic and spectroscopic analyses to evaluate sample quality.