Obesity may confer cardiac dysfunction due to lipid accumulation in cardiomyocytes. To test this idea, we examined whether obese ob/ob mice display heart lipid accumulation and cardiac dysfunction. Ob/ob mouse hearts had increased expression of genes mediating extracellular generation, transport across the myocyte cell membrane, intracellular transport, mitochondrial uptake, and β-oxidation of fatty acids compared with ob/+ mice. Accordingly, ob/ob mouse hearts contained more triglyceride (6.8 ± 0.4 vs. 2.3 ± 0.4 μg/mg; P < 0.0005) than ob/+ mouse hearts. Histological examinations showed marked accumulation of neutral lipid droplets within cardiac myocytes but not increased deposition of collagen between myocytes in ob/ob compared with ob/+ mouse hearts. On echocardiography, the ratio of E to A transmitral flow velocities (an indicator of diastolic function) was 1.8 ± 0.1 in ob/ob mice and 2.5 ± 0.1 in ob/+ mice (P = 0.0001). In contrast, the indexes of systolic function and heart brain natriuretic peptide mRNA expression were only marginally affected and unaffected, respectively, in ob/ob compared with ob/+ mice. The results suggest that ob/ob mouse hearts have increased expression of cardiac gene products that stimulate myocyte fatty acid uptake and triglyceride storage and accumulate neutral lipids within the cardiac myocytes. The results also suggest that the cardiac lipid accumulation is paralleled by cardiac diastolic dysfunction in ob/ob mice.

The heart secretes apolipoprotein B (apoB) containing lipoproteins. Herein, we examined whether the overexpression of a human apoB transgene in the heart affects triglyceride accumulation and development of cardiac dysfunction in streptozotocin-treated diabetic mice. Blood glucose, plasma free fatty acids, and plasma triglycerides were similarly affected in diabetic wild type mice and diabetic apoB transgenic mice as compared with non-diabetic mice of the same genotype. After 12 weeks, heart triglycerides were increased by 48% in diabetic wild type mice. These mice displayed an increased expression of brain natriuretic peptide and deterioration of heart function on echocardiography. In diabetic apoB transgenic mice, heart triglyceride levels were identical to those in non-diabetic wild type and apoB transgenic mice, and brain natriuretic peptide expression as well as echocardiographic indexes of heart function were only marginally affected or unaffected. The findings suggest that triglyceride accumulation in the heart is important for development of diabetic cardiomyopathy in mice, and that lipoprotein formation by cardiomyocytes plays an integrated role in cardiac lipid metabolism.Liver and intestinal cells secrete triglyceride-rich lipoproteins. This ability is dependent on the expression of the apoB and microsomal triglyceride transfer protein (MTP) 1 genes (1, 2). MTP transfers triglycerides onto the apoB polypeptide chain during its translation into the endoplasmic reticulum. ApoB serves as the principal structural protein in the resulting lipoprotein particles that are secreted from the cells. Studies of mice, which overexpress a human apoB transgene, revealed that cardiac myocytes in addition to hepatocytes and absorptive enterocytes also express the apoB and MTP genes (3) and secrete apoB containing lipoproteins (4). The apoB mRNA is not edited in cardiac myocytes (5). Consequently, the heart secretes lipoproteins containing the full-length apoB100 protein rather than the truncated apoB48 protein (4). Because the formation of apoB-containing lipoproteins serves as an effective means of secreting large amounts of triglycerides from liver and intestinal cells, we hypothesized previously that the physiological role of lipoprotein formation in the heart could be the removal of triglycerides from myocytes that are not used as fuel, i.e. a reverse triglyceride transport pathway (6, 7).Recently, the idea has been put forward that triglyceride accumulation in cardiac muscle cells adversely affects cardiac function (8). Diabetes is associated with aberrations in cardiac fuel metabolism and a ϳ2-fold increase in cardiac triglyceride content (9, 10). In diabetic rats, this triglyceride accumulation occurs in parallel with compromised cardiac performance (11,12). Echocardiographic studies have also revealed abnormal cardiac function in young diabetic individuals without coronary heart disease (13). It is unknown as to what extent triglyceride accumulation in cardiac myocytes affects the development of diabetes-ind...

To investigate the association between hyperinsulinemia and cardiac hypertrophy, we treated rats with insulin for 7 wk and assessed effects on myocardial growth, vascularization, and fibrosis in relation to the expression of angiotensin II receptors (AT-R). We also characterized insulin signaling pathways believed to promote myocyte growth and interact with proliferative responses mediated by G protein-coupled receptors, and we assessed myocardial insulin receptor substrate-1 (IRS-1) and p110 alpha catalytic and p85 regulatory subunits of phospatidylinositol 3 kinase (PI3K), Akt, MEK, ERK1/2, and S6 kinase-1 (S6K1). Left ventricular (LV) geometry and performance were evaluated echocardiographically. Insulin decreased AT1a-R mRNA expression but increased protein levels and increased AT2-R mRNA and protein levels and phosphorylation of IRS-1 (Ser374/Tyr989), MEK1/2 (Ser218/Ser222), ERK1/2 (Thr202/Tyr204), S6K1 (Thr421/Ser424/Thr389), Akt (Thr308/Thr308), and PI3K p110 alpha but not of p85 (Tyr508). Insulin increased LV mass and relative wall thickness and reduced stroke volume and cardiac output. Histochemical examination demonstrated myocyte hypertrophy and increases in interstitial fibrosis. Metoprolol plus insulin prevented the increase in relative wall thickness, decreased fibrosis, increased LV mass, and improved function seen with insulin alone. Thus our data demonstrate that chronic hyperinsulinemia decreases AT1a-to-AT2 ratio and increases MEK-ERK1/2 and S6K1 pathway activity related to hypertrophy. These changes might be crucial for increased cardiovascular growth and fibrosis and signs of impaired LV function.

BackgroundThe management of the cardiorenal syndrome in advanced heart failure is challenging, and the role of inotropic drugs has not been fully defined. Our aim was to compare the renal effects of levosimendan versus dobutamine in patients with heart failure and renal impairment.Methods and ResultsIn a randomized double‐blind study, we assigned patients with chronic heart failure (left ventricular ejection fraction <40%) and impaired renal function (glomerular filtration rate <80 mL/min per 1.73 m2) to receive either levosimendan (loading dose 12 μg/kg+0.1 μg/kg per minute) or dobutamine (7.5  μg/kg per minute) for 75 minutes. A pulmonary artery catheter was used for measurements of systemic hemodynamics, and a renal vein catheter was used to measure renal plasma flow by the infusion clearance technique for PAH (para‐aminohippurate) corrected by renal extraction of PAH. Filtration fraction was measured by renal extraction of chromium ethylenediamine tetraacetic acid. A total of 32 patients completed the study. Following treatment, the levosimendan and dobutamine groups displayed similar increases in renal blood flow (22% and 26%, respectively) with no significant differences between groups. Glomerular filtration rate increased by 22% in the levosimendan group but remained unchanged in the dobutamine group (P=0.012). Filtration fraction was not affected by levosimendan but decreased by 17% with dobutamine (P=0.045).ConclusionsIn patients with chronic heart failure and renal impairment, levosimendan increases glomerular filtration rate to a greater extent than dobutamine and thus may be the preferred inotropic agent for treating patients with the cardiorenal syndrome.Clinical Trial RegistrationURL: https://www.clinicaltrials.gov. Unique identifier: NCT02133105.