Assessment of sarcoplasmic reticulum Ca2+-uptake during the development of left ventricular hypertrophy

Nootkatone, a Dietary Fragrant Bioactive Compound, Attenuates Dyslipidemia and Intramyocardial Lipid Accumulation and Favorably Alters Lipid Metabolism in a Rat Model of Myocardial Injury: An In Vivo and In Vitro Study

In the present study, we assessed whether nootkatone (NKT), a sesquiterpene in edible plants, can provide protection against dyslipidemia, intramyocardial lipid accumulation, and altered lipid metabolism in a rat model of myocardial infarction (MI) induced by subcutaneous injections of isoproterenol (ISO, 85 mg/kg) on days 9 and 10. The rats were pre- and co-treated with NKT (10 mg/kg, p.o.) administered daily for 11 days. A significant reduction in the activities of myocardial creatine kinase and lactate dehydrogenase, as well as non-enzymatic antioxidants, and alterations in lipids and lipoproteins, along with a rise in plasma lipid peroxidation and intramyocardial lipid accumulation, were observed in ISO-treated rats. ISO administration induced alterations in the activities of enzymes/expressions that played a significant role in altering lipid metabolism. However, NKT treatment favorably modulated all biochemical and molecular parameters altered by ISO and showed protective effects against oxidative stress, dyslipidemia, and altered lipid metabolism, attributed to its free-radical-scavenging and antihyperlipidemic activities in rats with ISO-induced MI. Additionally, NKT decreased the accumulation of lipids in the myocardium as evidenced from Oil red O staining. Furthermore, the in vitro observations demonstrate the potent antioxidant property of NKT. The present study findings are suggestive of the protective effects of NKT on dyslipidemia and the underlying mechanisms. Based on our findings, it can be suggested that NKT or plants rich in NKT can be promising for use as a phytopharmaceutical or nutraceutical in protecting the heart and correcting lipid abnormalities and dyslipidemia, which are risk factors for ischemic heart diseases.

Sarcoplasmic reticulum and calcium signaling in muscle cells: Homeostasis and disease

The sarco/endoplasmic reticulum is an extensive, dynamic and heterogeneous membranous network that fulfills multiple homeostatic functions. Among them, it compartmentalizes, stores and releases calcium within the intracellular space. In the case of muscle cells, calcium released from the sarco/endoplasmic reticulum in the vicinity of the contractile machinery induces cell contraction. Furthermore, sarco/endoplasmic reticulum-derived calcium also regulates gene transcription in the nucleus, energy metabolism in mitochondria and cytosolic signaling pathways. These diverse and overlapping processes require a highly complex fine-tuning that the sarco/endoplasmic reticulum provides by means of its numerous tubules and cisternae, specialized domains and contacts with other organelles. The sarco/endoplasmic reticulum also possesses a rich calcium-handling machinery, functionally coupled to both contraction-inducing stimuli and the contractile apparatus. Such is the importance of the sarco/endoplasmic reticulum for muscle cell physiology, that alterations in its structure, function or its calcium-handling machinery are intimately associated with the development of cardiometabolic diseases. Cardiac hypertrophy, insulin resistance and arterial hypertension are age-related pathologies with a common mechanism at the muscle cell level: the accumulation of damaged proteins at the sarco/endoplasmic reticulum induces a stress response condition termed endoplasmic reticulum stress, which impairs proper organelle function, ultimately leading to pathogenesis.

Cardioprotective effect of nesfatin-1 against isoproterenol-induced myocardial infarction in rats: Role of the Akt/GSK-3β pathway

The present study was designed to evaluate the cardioprotective effects of nesfatin-1, a novel peptide with anorexigenic properties, in rats with isoproterenol (ISO)-induced myocardial infarction (MI), and to further investigate the role of Akt/GSK-3β signaling pathway in the protective effect of nesfatin-1. To induce MI, ISO was subcutaneously injected into the rats for two consecutive days at a dosage of 85mg/kg/day. ISO-induced myocardial damage was indicated by elevated levels of cardiac specific troponin-T, enhanced myocardial expression of proinflammatory cytokines (interleukin-1β, interleukin-6 and tumor necrosis factor-α), and increased number of cells with apoptotic and necrotic appearance in the myocardial tissue. Levels of p-Akt/Akt and p-GSK-3β/GSK-3β significantly decreased in heart tissue after ISO-induced MI. However, intraperitoneal administration of nesfatin-1 (10μg/kg/day) elicited a significant cardioprotective activity by lowering the levels of cardiac troponin-T and proinflammatory cytokines, indicating the protective effect of nesfatin-1 against ISO-induced MI. The biochemical findings were further confirmed by histopathological examination, which was demonstrated by reduced number of apoptotic and necrotic cells. Moreover, expressions of p-Akt/Akt and p-GSK-3β/GSK-3β in the myocardium of MI group rats were significantly increased by nesfatin-1 administration, suggesting that nesfatin-1, which appears to possess anti-apoptotic and anti-inflammatory properties, may confer protection against ISO-induced MI via an Akt/GSK-3β-dependent mechanism.

A biochemical and 2, 3, 5-triphenyl tetrazolium chloride staining study on the preventive effects of zingerone (vanillyl acetone) in experimentally induced myocardial infarcted rats

Myocardial infarction continues to be a major public health problem, not only in western countries but also increasingly in developing countries and makes significant contribution to the mortality statistics. Reduction in mortality rate and prevention of myocardial infarction are of utmost importance. Tachycardia, left ventricular hypertrophy (LVH), altered adenosine triphosphatases (ATPases), and shifts in electrolyte balance play a vital role in the pathogenesis of myocardial infarction. This study was designed to evaluate the preventive effects of zingerone (vanillyl acetone) on tachycardia, LVH, altered electrocardiogram (ECG), altered activities of membrane bound ATPases, electrolyte imbalance and myocardial infarct size in isoproterenol induced myocardial infarcted rats. Rats were pretreated with zingerone (vanillyl acetone) 6 mg/kg body weight daily for a period of 14 days and were then induced myocardial infarction with isoproterenol (100 mg/kg body weight) on 15th and 16th day. Isoproterenol induced myocardial infarcted rats showed tachycardia, LVH, altered ECG, serum cardiac troponin-T, plasma myoglobin, heart ATPases, heart sodium ion, calcium ion, potassium ion, and increased myocardial infarct size. Pretreatment with zingerone (vanillyl acetone) revealed preventive effects on tachycardia, LVH, ECG, and all the above mentioned biochemical parameters evaluated in isoproterenol induced myocardial infarcted rats. The 2, 3, 5-triphenyl tetrazolium chloride staining on myocardial infarct size confirmed the prevention of myocardial infarction. Further, the in vitro study revealed a very convincing free radical scavenging of zingerone (vanillyl acetone). Thus, the observed effects of zingerone (vanillyl acetone) are due to its antioxidant and free radical scavenging activities in isoproterenol induced myocardial infarcted rats.

Ellagic acid inhibits cardiac arrhythmias, hypertrophy and hyperlipidaemia during myocardial infarction in rats

OBJECTIVE

The objective was to evaluate the protective effect of ellagic acid against experimentally induced cardiac arrhythmias, hypertrophy and its association with altered lipid metabolism during myocardial infarction in rats.

METHODS

Rats were treated with ellagic acid (7.5 and 15 mg/kg) orally for a period of 10 days. After 10 days of pretreatment, isoproterenol (100 mg/kg) was injected subcutaneously at an interval of 24 h for 2 days to induce myocardial infarction. On the 12th day, the cardiac rhythm was observed. The rats were sacrificed and the heart was isolated from each rat. Ventricular hypertrophy and myocardial necrotic scores were analysed in the myocardium. Lipid peroxidation products in the plasma were analysed. Changes in the lipid profile were measured using the plasma and heart tissue homogenates of normal and experimental rats.

RESULTS

Isoproterenol-induced rats showed arrhythmias, hypertrophy and increased levels of myoglobin, creatine kinase-MB, lipid peroxidation products compared to the normal control rats. Ventricular hypertrophy and increased myocardial necrotic scores were observed in isoproterenol-induced rats. Oral pretreatment with ellagic acid restored pathological arrhythmias, ventricular hypertrophy, lipid peroxidation, altered lipid profile and myocardial necrosis in the isoproterenol-induced myocardial infarcted rats.

CONCLUSIONS

Oral pretreatment with ellagic acid was safe and effective in cardio protection against ISO-induced arrhythmias, hypertrophy and myocardial necrosis. Anti lipid peroxidation property and anti hyperlipidaemic activity through 3-hydroxy-3 methyl glutaryl CoA reductase inhibition by ellagic acid may be the reasons for the beneficial action of ellagic acid against experimentally induced myocardial infarction.

Regulation of phospholamban and sarcoplasmic reticulum Ca2+-ATPase by atorvastatin: implication for cardiac hypertrophy

Abnormal intracellular Ca2+ homeostasis in the myocardium has been suggested as the cause of cardiac hypertrophy, and this process can be prevented by the HMG-CoA reductase inhibitors, statins. In the present study, the effect of atorvastatin on left ventricular hypertrophy was investigated, and then whether the underlying mechanism was related to a defect in intracellular Ca2+ homeostasis explored. Twelve spontaneously hypertensive rats (SHR), at 8 weeks old, were used in this study, and received either distilled water or atorvastatin for ten weeks, with age-matched normotensive Wistar-Kyoto rats (WKY) used as controls. RT-PCR and western blotting were used to detect the mRNA and protein expressions of phospholamban (PLB) and sarcoplasmic reticulum Ca2+-ATPase (SERCA2a), respectively, and a colorimetric method used to examine the SERCA2a activity. Additionally, cardiac hypertrophic indices, such as the cardiosomatic ratio, left ventricular weight to body weight (LVW/BW) ratio and cardiomyocytes transverse diameter (TDM), together with the systolic blood pressure (SBP) and serum lipids levels were also examined. After ten weeks, significant decreases were observed in both the mRNA and protein expression levels of SERCA2a, as well as its activity, in the hypertrophied hearts of the SHR. The administration of atorvastatin to the same strains of rats effectively inhibited these decreases, and the above cardiac hypertrophic indices, as well as the SBP and serum lipids levels were significantly decreased. However, no significant changes in the expressions of PLB were observed in WKY, SHR and atorvastatin-treated SHR. These findings demonstrated that through regulation of the PLB and SERCA2a levels in the hearts of SHR, atorvastatin can prevent the cardiac hypertrophy caused due to pressure overload, which provides a relatively new insight into the mechanism of atorvastatin in the prevention of cardiac hypertrophy.

Mechanistic basis of differences in Ca2+ -handling properties of sarcoplasmic reticulum in right and left ventricles of normal rat myocardium

This study investigated Ca2+ -cycling properties of sarcoplasmic reticulum (SR) in right ventricle (RV) and left ventricle (LV) of normal rat myocardium. Intracellular Ca2+ transients and contractile function were monitored in freshly isolated myocytes from RV and LV. SR in RV displayed nearly fourfold lower rates of ATP-energized Ca2+ uptake in vitro than SR of LV. The Ca2+ concentration required for half-maximal activation of Ca2+ transport was nearly twofold higher in SR of RV. The lower Ca2+ -sequestering activity of SR in RV was accompanied by a matching decrement in Ca2+ -induced phosphoenzyme formation during the catalytic cycle of the Ca2+ -pumping ATPase (SERCA2). Western immunoblot analysis showed that protein levels of Ca2+ -ATPase and its inhibitor phospholamban (PLN) were only approximately 15% lower in SR of RV than in SR of LV. Coimmunoprecipitation experiments revealed that PLN-bound, functionally inert Ca2+ -ATPase molecules in SR of RV greatly exceed (> 50%) that in SR of LV. Endogenous Ca2+/calmodulin-dependent protein kinase-mediated phosphorylation of SR substrates did not abolish the huge disparity in SR Ca2+ pump function between RV and LV. Intracellular Ca2+ transients, evoked by electrical field stimulation, were significantly prolonged in RV myocytes compared with LV myocytes, mainly because of slow decay of intracellular Ca2+ concentration. The slow decay of intracellular Ca2+ concentration in RV and consequent decrease in the speed of RV relaxation may promote temporal synchrony of the end of diastole in RV and LV. The preponderance of functionally silent SR Ca2+ pumps in RV reflects a higher diastolic reserve required to protect and maintain RV function in the face of a sudden rise in afterload or resistance in the pulmonary circulation.

Reduced inhibitor 1 and 2 activity is associated with increased protein phosphatase type 1 activity in left ventricular myocardium of one-kidney, one-clip hypertensive rats

In failing hearts, although protein phosphatase type 1 (PP1) activity has increased, information about the regulation and status of PP1 inhibitor-1 (INH-1) and inhibitor-2 (INH-2) is limited. In this study, we examined activity and protein expression of PP1, INH-1 and INH-2 and phosphorylation of sarcoplasmic reticulum (SR) phospholamban (PLB), a substrate of PP1 and modulator of SR Ca2+-ATPase activity, in failing and non-failing hearts. These studies were performed in LV myocardium of seven rats with chronic renal hypertension produced by Goldblatt's one-kidney, one-clip procedure and seven age-matched sham-operated normal controls (CTR). Eight weeks after surgery, LV ejection fraction, LV hypertrophy, and pulmonary congestion were determined in all rats. PP1 activity (nmol 32P/min/mg non-collagen protein) was assessed in LV homogenates using 32P-labeled phosphorylase a as substrate. INH-1 and INH-2 activity was determined in the immunoprecipitate of LV homogenates and expressed as percentage inhibitory activity. Using a specific antibody, LV tissue levels of PP1C and calsequestrin (CSQ), a SR calcium binding protein, which is not altered in failing hearts, were also determined. Further, total and phosphorylated PLB, INH-1 and INH-2 protein levels were determined in the LV homogenate and phosphoprotein-enriched fraction, respectively. The band density of each protein was quantified in densitometric units and normalized to CSQ.

RESULTS

rats with chronic renal hypertension exhibited significantly reduced LV ejection fraction and increased LV hypertrophy and pulmonary congestion, characteristics of chronic heart failure (CHF). We found that compared to CTR, (1) both INH-1 (10.2+/-2 versus 57.5+/-1; p < 0.05) and INH-2 activity (3.8+/-0.4 versus 36.2+/-4; p < 0.05) were reduced, (2) total and phosphorylated PLB amount reduced, (3) protein level of phosphorylated INH-1 was reduced (2.32+/-0.1 versus 0.73+/-0.04; p < 0.05) whereas that of phosphorylated INH-2 increased (3.05+/-0.3 versus 1.42+/-0.1; p < 0.05), and (4) PP1 activity was increased approximately 2.6-fold in rats with CHF (1.59+/-0.05 versus 0.61+/-0.01; p < 0.05) while protein level of the catalytic subunit of PP1 (PP1C) increased 3.85-fold (0.77+/-0.05 versus 0.20+/-0.02; p < 0.05). These results suggest that reduced inhibitory INH-1 and INH-2 activity, increased PP1C protein level, and reduced PLB phosphorylation are associated with increased PP1 activity in failing hearts.

The cardiac support device and the myosplint: treating heart failure by targeting left ventricular size and shape

Left ventricular (LV) remodeling occurs in patients with heart failure and is associated with poor long-term outcome. Two important components of this remodeling process are progressive LV dilation and LV shape changes, the latter manifested by increased LV chamber sphericity. This brief review describes two passive mechanical devices that were developed to prevent the progressive LV dilation and shape changes that occur during the evolution of heart failure. One such device is the Cardiac Support Device ([CSD] CorCap; Acorn Cardiovascular, St Paul, MN) and the other is the Myosplint (Myocor, Maple Grove, MN). Studies in dogs with coronary microembolization-induced heart failure have shown that the CSD prevents progressive LV dilation, increases LV ejection fraction, lowers LV wall stress, and attenuates LV chamber sphericity. Safety and feasibility studies in patients with heart failure have shown that the CSD is safe. The same studies have provided strong efficacy trends that are consistent with those seen in experimental animals. Studies in dogs with rapid pacing induced heart failure showed that the Myosplint device can reshape the LV leading to reduced LV volumes, increased ejection fraction, and reduced wall stress. Safety and feasibility studies of the Myosplint device in humans are limited and trends are not as yet easily discerned. Final conclusions on the clinical effectiveness of these devices must await completion of randomized clinical trials. These trials should provide the first tests in humans of the hypothesis that limiting LV remodeling alone can improve long-term outcome and quality of life in patients with heart failure.