Carnitine palmitoyltransferase-I, a new target for the treatment of heart failure: perspectives on a shift in myocardial metabolism as a therapeutic intervention

Untargeted metabolomics reveals the combination effects and mechanisms of Huangqi-fuzi herb-pair against doxorubicin-induced cardiotoxicity

ETHNOPHARMACOLOGICAL RELEVANCE

Qifu decoction (QFD) is a famous traditional Chinese medicine (TCM) composed of Astragali Radix (HuangQi) and Aconiti Lateralis Radix Praeparaia (Fuzi), which can alleviate doxorubicin (DOX)-induced cardiotoxicity (DIC). However, its protective mechanism remains obscured.

AIM OF THE STUDY

The present study aimed to uncover the cardioprotective mechanism and the synergistic effect of QFD against DIC in mice.

MATERIALS AND METHODS

The cardioprotective activity of QFD against DIC was assessed by electrocardiogram, serum biochemical assays and histopathology. Mass spectrometry-based metabolomic approach was conducted to elucidate the preventive mechanisms of QFD, HuangQi decoction (HQD), and Fuzi decoction (FZD) against DIC. QFD, HQD, FZD-targeted metabolic pathways were identified and compared to investigate the synergistic mechanism of QFD by computational systems analysis. Quantitative real-time PCR (qRT-PCR) was further employed to validate the key metabolic pathways at the level of the gene.

RESULTS

The electrocardiogram combined with the biochemical analysis and histopathology showed that the protection effects were sorted as QFD > HQD ≈ FZD. A total of 41 metabolites contributing to DIC were identified in the mice serum, among which 32, 12 and 10 metabolites were significantly reverted by QFD, HQD and FZD, respectively. Metabolic pathway analysis revealed that DOX perturbed 12 metabolic pathways, and QFD, HQD, and FZD-treated groups could significantly reverse 12, 7 and 6 metabolic pathways of these 12 metabolic pathways. Metabolic pathway and qRT-PCR revealed that QFD could protect DIC mainly by regulating energy metabolism, amino acids metabolism, arachidonic acid metabolism and glycerophospholipid metabolism, and HQD and FZD mutually reinforced each other.

CONCLUSION

These evidences revealed that QFD was a promising drug candidate for DIC by maintaining metabolic homeostasis. Meanwhile, this work provided a useful approach for evaluating the efficacy and the synergistic effects of TCMs against cardiomyopathy.

Effect of DanQi Pill on PPARα, lipid disorders and arachidonic acid pathway in rat model of coronary heart disease

Background

Danqi pill (DQP) is one of the most widely prescribed formulas and has been shown to have remarkable protective effect on coronary heart disease (CHD). However, its regulatory effects on lipid metabolism disorders haven’t been comprehensively studied so far. We aimed to explore the effects of DQP on Peroxisome Proliferator activated receptors α (PPARα), lipid uptake-transportation-metabolism pathway and arachidonic acid (AA)-mediated inflammation pathway in rats with CHD.

Methods

80 Sprague-Dawley (SD) Rats were randomly divided into sham group, model group, positive control group and DQP group. Rat model of CHD was induced by ligation of left ventricle anterior descending artery and fed with high fat diet in all but the sham group. Rats in sham group only underwent thoracotomy. After surgery, rats in the positive control and DQP group received daily treatments of pravastatin and DQP respectively. At 28 days after surgery, rats were sacrificed and plasma lipids were evaluated by plasma biochemical detection. Western blot and PCR were applied to evaluate the expressions of PPARα, proteins involved in lipid metabolism and AA pathways.

Results

Twenty eight days after surgery, dyslipidemia developed in CHD model rats, as illustrated by elevated plasma lipid levels. Expressions of apolipoprotein A-I (ApoA-I), cluster of differentiation 36 (CD36) and fatty acid binding protein (FABP) in the heart tissues of model group were down-regulated compared with those in sham group. Expressions of carnitine palmitoyl transferase I (CPT-1A) and lipoproteinlipase (LPL) were also reduced significantly. In addition, levels of phospholipase A2 (PLA2) and cyclooxygenase 2 (COX-2) were up-regulated. Expressions of Nuclear factor-κB (NF- κB) and signal transducer and activator of transcription 3 (STAT3) also increased. Furthermore, Expression of PPARα decreased in the model group. DQP significantly up-regulated expressions of ApoA-I and FABP, as well as the expressions of CPT-1A and CD36. In addition, DQP down-regulated expressions of PLA2, COX-2 and NF-κB in inflammation pathway. Levels of STAT3 and LPL were not affected by DQP treatment. In particular, DQP up-regulated PPARα level significantly.

Conclusions

DQP could effectively regulate lipid uptake-transportation-metabolism process in CHD model rats, and the effect is achieved mainly by activating ApoA-I-CD36-CPT-1A molecules. Interestingly, DQP can up-regulate expression of PPARα significantly. The anti-inflammatory effect of DQP is partly exerted by inhibiting expressions of PLA2-COX2 -NF-κB pathway.

Loss of stearoyl-CoA desaturase 1 rescues cardiac function in obese leptin-deficient mice

The heart of leptin-deficient ob/ob mice is characterized by pathologic left ventricular hypertrophy along with elevated triglyceride (TG) content, increased stearoyl-CoA desaturase (SCD) activity, and increased myocyte apoptosis. In the present study, using an ob/ob;SCD1(-/-) mouse model, we tested the hypothesis that lack of SCD1 could improve steatosis and left ventricle (LV) function in leptin deficiency. We show that disruption of the SCD1 gene improves cardiac function in ob/ob mice by correcting systolic and diastolic dysfunction without affecting levels of plasma TG and FFA. The improvement is associated with reduced expression of genes involved in FA transport and lipid synthesis in the heart, as well as reduction in cardiac FFA, diacylglycerol, TG, and ceramide levels. The rate of FA beta-oxidation is also significantly lower in the heart of ob/ob;SCD1(-/-) mice compared with ob/ob controls. Moreover, SCD1 deficiency reduces cardiac apoptosis in ob/ob mice due to increased expression of antiapoptotic factor Bcl-2 and inhibition of inducible nitric oxide synthase and caspase-3 activities. Reduction in myocardial lipid accumulation and inhibition of apoptosis appear to be one of the main mechanisms responsible for improved LV function in ob/ob mice caused by SCD1 deficiency.

Loss of stearoyl-CoA desaturase 1 inhibits fatty acid oxidation and increases glucose utilization in the heart

Stearoyl-CoA desaturase (SCD) is a lipogenic enzyme that catalyzes the synthesis of monounsaturated fatty acids (FA). SCD1 deficiency activates metabolic pathways that promote FA beta-oxidation and decrease lipogenesis in liver. In the present study, we show that FA transport and oxidation are decreased, whereas glucose uptake and oxidation are increased in the heart of SCD1(-/-) mice. Protein levels of FA transport proteins such as FA translocase/CD36 and FA transport protein as well as activity of carnitine palmitoyltransferase 1, the rate-limiting enzyme for mitochondrial fat oxidation, were significantly lower in the heart of SCD1(-/-) mice compared with SCD1(+/+) mice. Consequently, the rate of palmitoyl-CoA oxidation was decreased significantly in the heart of SCD1(-/-) mice. mRNA levels of peroxisome proliferator-activated receptor-alpha, a key transcription factor controlling genes of FA oxidation, were significantly reduced in SCD1(-/-) mice. Phosphorylation of insulin receptor substrate-1 (IRS-1) and the association of alphap85 subunit of phosphatidylinositol 3-kinase with IRS-1 were significantly higher under both basal and insulin-stimulated conditions in SCD1(-/-) hearts. This increased insulin sensitivity translated to a 1.8-fold greater 2-deoxyglucose uptake and 2-fold higher rate of glucose oxidation in the myocardium compared with SCD1(+/+) counterparts. The results suggest that SCD1 deficiency causes a shift in cardiac substrate utilization from FA to glucose by upregulating insulin signaling, decreasing FA availability, and reducing expression of FA oxidation genes in the heart. This increase in cardiac insulin sensitivity and glucose utilization due to SCD1 deficiency could prove therapeutic in pathological conditions such as obesity that are characterized by skewed cardiac substrate utilization.

Pharmacological profile of the new inotropic agent AT-11

Although there are many classes of drugs, including cardiac glycosides, sympathomimetic inotropes, beta-adrenergic antagonists, angiotensin-converting enzyme inhibitors (ACE inhibitors) and spironolactone etc. used for the treatment of heart failure, the morbidity and mortality rates of patients after these treatments are not ameliorated. Chronic administration of Sympathomimetic inotropes also increased the arrhythmogenic effects. Consequently, improvement of treatment for heart failure remains a major medical challenge for the coming years. In this present experiment, the novel Na(+)-K(+) ATPase inhibitor AT-11 was characterized for its inotropic and toxic properties. Comparing AT-11 with ouabain, we found that AT-11 concentration-dependently increased contractility in guinea pig heart preparations, and the safety index of AT-11 was better than ouabain in vitro. In the in vivo study, AT-11 was also safer than ouabain at the equieffective dose. Moreover, AT-11 slowed heart rate more than ouabain did. This may be due to a larger AT-11-induced increase in vagal reflex than with ouabain and an indirect decrease in sympathetic tone to prevent Ca(2+) overload.

Role of subcellular remodeling in cardiac dysfunction due to congestive heart failure

Although alterations in the size and shape of the heart (cardiac remodeling) are considered in explaining cardiac dysfunction during the development of congestive heart failure (CHF), there are several conditions including initial stages of cardiac hypertrophy, where cardiac remodeling has also been found to be associated with either an increased or no change in heart function. Extensive studies have indicated that cardiac dysfunction is related to defects in one or more subcellular organelles such as myofibrils, sarcoplasmic reticulum and sarcolemma, depending upon the stage of CHF. Such subcellular abnormalities in the failing hearts have been shown to occur at both genetic and protein levels. Blockade of the renin-angiotensin system has been reported to partially attenuate changes in subcellular protein, gene expression, functional activities and cardiac performance in CHF. These observations provide support for the role of subcellular remodeling (alterations in molecular and biochemical composition of subcellular organelles) in cardiac dysfunction in the failing heart. On the basis of existing knowledge, it appears that subcellular remodeling during the process of cardiac remodeling plays a major role in the development of cardiac dysfunction in CHF.

Crystal structures of murine carnitine acetyltransferase in ternary complexes with its substrates

Carnitine acyltransferases catalyze the reversible exchange of acyl groups between coenzyme A (CoA) and carnitine. They have important roles in many cellular processes, especially the oxidation of long-chain fatty acids in the mitochondria for energy production, and are attractive targets for drug discovery against diabetes and obesity. To help define in molecular detail the catalytic mechanism of these enzymes, we report here the high resolution crystal structure of wild-type murine carnitine acetyltransferase (CrAT) in a ternary complex with its substrates acetyl-CoA and carnitine, and the structure of the S554A/M564G double mutant in a ternary complex with the substrates CoA and hexanoylcarnitine. Detailed analyses suggest that these structures may be good mimics for the Michaelis complexes for the forward and reverse reactions of the enzyme, representing the first time that such complexes of CrAT have been studied in molecular detail. The structural information provides significant new insights into the catalytic mechanism of CrAT and possibly carnitine acyltransferases in general.

Myocardial protection from ischemic preconditioning is not blocked by sub-chronic inhibition of carnitine palmitoyltransferase I

Ischemic preconditioning (IP) triggers cardioprotection via a signaling pathway that converges on mitochondria. The effects of the inhibition of carnitine palmitoyltransferase I (CPT-I), a key enzyme for transport of long chain fatty acids (LCFA) into the mitochondria, on ischemia/reperfusion (I/R) injury are unknown. Here we investigated, in isolated perfused rat hearts, whether sub-chronic CPT-I inhibition (5 days i.p. injection of 25 mg/kg/day of Etomoxir) affects I/R-induced damages and whether cardioprotection by IP can be induced after this inhibition. Effects of global ischemia (30 min) and reperfusion (120 min) were examined in hearts harvested from Control (untreated), Vehicle- or Etomoxir-treated animals. In subsets of hearts from the three treated groups, IP was induced by three cycles of 3 min ischemia followed by 10 min reperfusion prior to I/R. The extent of I/R injury under each condition was assessed by changes in infarct size as well as in myocardial contractility. Postischemic contractility, as indexed by developed pressure and dP/dt(max), was similarly affected by I/R, and was similarly improved with IP in Control, Vehicle or Etomoxir treated animals. Infarct size was also similar in the three subsets without IP, and was significantly reduced by IP regardless of CPT-I inhibition. We conclude that CPT-I inhibition does not affect I/R damages. Our data also show that IP affords myocardial protection in CPT-I inhibited hearts to a degree similar to untreated animals, suggesting that a long-term treatment with the metabolic anti-ischemic agent Etomoxir does not impede the possibility to afford cardioprotection by ischemic preconditioning.

Altered inotropic reactivity in diabetic rabbit right ventricular myocardium

Alloxan monohydrate was used to induce diabetes in rabbits, which were maintained for a 3-month period with or without daily insulin replacement along with age-matched controls. Isolated right ventricular myocardial strips were used to generate dose–response curves to isoproterenol, forskolin, and Bay K 8644. Basal developed force was significantly elevated in diabetic ventricular strips. While isoproterenol acted as a full inotropic agonist, diabetic preparations revealed a consistent but insignificant decrease in the maximum developed force. While both sensitivity to isoproterenol and β-adrenoceptor density were decreased in preparations from diabetic rabbits, there was no associated increase in circulating plasma catecholamines. In contrast, forskolin and Bay K 8644 were partial agonists in control preparations but full inotropic agonists in diabetic preparations, demonstrating significant increases in maximum developed force. This hyperresponsiveness was not associated with altered calcium channel density. Finally, insulin replacement reduced or prevented all diabetic-related changes. These data indicate that the hyperresponsiveness to forskolin and Bay K 8644 represents an altered utilization of intracellular calcium in the diabetic rabbit, converting them into full agonists similar to isoproterenol. The decrease in sensitivity to isoproterenol correlated with a decrease in β-adrenoceptor density but not elevated circulating catecholamines as previously observed in diabetic rats.Key words: experimental diabetes, β-adrenoceptor density, inotropic state, hyperresponsiveness, subsensitivity, calcium utilization.