Targeting the glucagon receptor improves cardiac function and enhances insulin sensitivity following a myocardial infarction

Qi Dan Li Xin pill improves chronic heart failure by regulating mTOR/p70S6k-mediated autophagy and inhibiting apoptosis

Myocardial remodeling represents a key factor in chronic heart failure (CHF) development, and is characterized by chronic death of cardiomyocytes. Cardiac function changes may be attributed to inflammation, apoptosis and autophagy. This study assessed the effects of Qi Dan Li Xin Pill (QD) on heart function, inflammatory factors, autophagy and apoptosis in cardiac remodeling in CHF rats upon myocardial infarction (MI) induction. Male SD rats underwent a sham procedure or left anterior descending coronary artery (LADCA) ligation, causing MI. Twenty-eight days after modeling, the animals were treated daily with QD, valsartan and saline for 4 weeks. Echocardiography after 4 weeks of drug intervention revealed substantially improved left ventricular remodeling and cardiac function following QD treatment. As demonstrated by decreased IL-1β, IL-6 and TNF-α amounts, this treatment also inhibited the apoptotic process and protected the viability of the myocardium. These outcomes may be attributed to enhanced autophagy in cardiomyocytes, which further reduced pro-inflammatory and pro apoptotic effects. This process may be achieved by QD regulation of the mTOR/P70S6K signaling pathway, suggesting that the traditional Chinese medicine Qi Dan Li Xin pill is effective in heart protective treatment, and is worth further investigation.

Tumor promoting effects of glucagon receptor: a promising biomarker of papillary thyroid carcinoma via regulating EMT and P38/ERK pathways

Glucagon is a crucial hormone involved in the maintenance of glucose homeostasis. Large efforts to define the role of glucagon receptor (GCGR) have been continuously made in recent years, but it is still incomplete about its function and mechanism. We performed this study to verify its potential impacts on papillary thyroid carcinoma (PTC) progression. Correlation between GCGR expression and PTC was elaborated using The Cancer Genome Atlas (TCGA) database. The Kaplan-Meier method was used to analyze the connection between GCGR expression and prognosis of PTC patients. GCGR expression was measured by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot analysis; simultaneously, cell viability was elucidated using cell proliferation and colony formation assays following siRNAs strategy. Transwell analyses were conducted to measure the invasion and migration of PTC cells. Flow cytometry analysis was conducted to examine apoptotic ability. The cAMP ELISA kit was employed to measure the cAMP level in PTC cells. Our data determined that the expression level of GCGR was increased in PTC tissues and cells in contrast to normal tissues and Nthy-ori 3-1, respectively. Up-regulated GCGR expression was linked with the lower survival rate in patients with PTC. Functional analysis in vitro suggested that GCGR knockdown attenuated PTC cell proliferation, colony formation, invasion, and migration whilst intensified apoptosis. Down-regulated GCGR was able to increase cAMP level. Furthermore, reduction of GCGR could result in the inactivation of epithelial-mesenchymal transition (EMT) and P38/ERK pathways. In conclusion, the findings of this study disclosed that GCGR promoted PTC cell behaviors by mediating the EMT and P38/ERK pathways, serving as a potential diagnostic and prognostic biomarker as well as therapeutic target for PTC.

Adropin regulates cardiac energy metabolism and improves cardiac function and efficiency

BACKGROUND

Impaired cardiac insulin signalling and high cardiac fatty acid oxidation rates are characteristics of conditions of insulin resistance and diabetic cardiomyopathies. The potential role of liver-derived peptides such as adropin in mediating these changes in cardiac energy metabolism is unclear, despite the fact that in skeletal muscle adropin can preferentially promote glucose metabolism and improve insulin sensitivity.

OBJECTIVES

To determine the influence of adropin on cardiac energy metabolism, insulin signalling and cardiac efficiency.

METHODS

C57Bl/6 mice were injected with either vehicle or a secretable form of adropin (450 nmol/kg, i.p.) three times over a 24-h period. The mice were fasted to accentuate the differences between animals in adropin plasma levels before their hearts were isolated and perfused using a working heart system. In addition, direct addition of adropin to the perfusate of ex vivo hearts isolated from non-fasting mice was utilized to investigate the acute effects of the peptide on heart metabolism and ex vivo function.

RESULTS

In contrast to the observed fasting-induced predominance of fatty acid oxidation as a source of ATP production in control hearts, insulin inhibition of fatty acid oxidation was preserved by adropin treatment. Adropin-treated mouse hearts also showed a higher cardiac work, which was accompanied by improved cardiac efficiency and enhanced insulin signalling compared to control hearts. Interestingly, acute adropin administration to isolated working hearts also resulted in an inhibition of fatty acid oxidation, accompanied by a robust stimulation of glucose oxidation compared to vehicle-treated hearts. Adropin also increased activation of downstream cardiac insulin signalling. Moreover, both in vivo and ex vivo treatment protocols induced a reduction in the inhibitory phosphorylation of pyruvate dehydrogenase (PDH), the major enzyme of glucose oxidation, and the protein levels of the responsible kinase PDH kinase 4 and the insulin-signalling inhibitory phosphorylation of JNK (p-T¹⁸³/Y¹⁸⁵) and IRS-1 (p-S³⁰⁷), suggesting acute receptor- and/or post-translational modification-mediated mechanisms.

CONCLUSIONS

These results demonstrate that adropin has important effects on energy metabolism in the heart and may be a putative candidate for the treatment of cardiac disease associated with impaired insulin sensitivity.

Epicardial adipose tissue predicts incident cardiovascular disease and mortality in patients with type 2 diabetes

Background

Cardiac fat is a cardiovascular biomarker but its importance in patients with type 2 diabetes is not clear. The aim was to evaluate the predictive potential of epicardial (EAT), pericardial (PAT) and total cardiac (CAT) fat in type 2 diabetes and elucidate sex differences.

Methods

EAT and PAT were measured by echocardiography in 1030 patients with type 2 diabetes. Follow-up was performed through national registries. The end-point was the composite of incident cardiovascular disease (CVD) and all-cause mortality. Analyses were unadjusted (model 1), adjusted for age and sex (model 2), plus systolic blood pressure, body mass index (BMI), low-density lipoprotein (LDL), smoking, diabetes duration and glycated hemoglobin (HbA_1c) (model 3).

Results

Median follow-up was 4.7 years and 248 patients (191 men vs. 57 women) experienced the composite end-point. Patients with high EAT (> median level) had increased risk of the composite end-point in model 1 [Hazard ratio (HR): 1.46 (1.13; 1.88), p = 0.004], model 2 [HR: 1.31 (1.01; 1.69), p = 0.038], and borderline in model 3 [HR: 1.32 (0.99; 1.77), p = 0.058]. For men, but not women, high EAT was associated with a 41% increased risk of CVD and mortality in model 3 (p = 0.041). Net reclassification index improved when high EAT was added to model 3 (19.6%, p = 0.035). PAT or CAT were not associated with the end-point.

Conclusion

High levels of EAT were associated with the composite of incident CVD and mortality in patients with type 2 diabetes, particularly in men, after adjusting for CVD risk factors. EAT modestly improved risk prediction over CVD risk factors.

Weight loss enhances cardiac energy metabolism and function in heart failure associated with obesity

AIMS

Obesity is associated with high rates of cardiac fatty acid oxidation, low rates of glucose oxidation, cardiac hypertrophy and heart failure. Whether weight loss can lessen the severity of heart failure associated with obesity is not known. We therefore determined the effect of weight loss on cardiac energy metabolism and the severity of heart failure in obese mice with heart failure.

MATERIALS AND METHODS

Obesity and heart failure were induced by feeding mice a high-fat (HF) diet and subjecting them to transverse aortic constriction (TAC). Obese mice with heart failure were then switched for 8 weeks to either a low-fat (LF) diet (HF TAC LF) or caloric restriction (CR) (40% caloric intake reduction, HF TAC CR) to induce weight loss.

RESULTS

Weight loss improved cardiac function (%EF was 38 ± 6% and 36 ± 6% in HF TAC LF and HF TAC CR mice vs 25 ± 3% in HF TAC mice, P < 0.05) and it decreased cardiac hypertrophy post TAC (left ventricle mass was 168 ± 7 and 171 ± 10 mg in HF TAC LF and HF TAC CR mice, respectively, vs 210 ± 8 mg in HF TAC mice, P < 0.05). Weight loss enhanced cardiac insulin signalling, insulin-stimulated glucose oxidation rates (1.5 ± 0.1 and 1.5 ± 0.1 μmol/g dry wt/min in HF TAC LF and HF TAC CR mice, respectively, vs 0.2 ± 0.1 μmol/g dry wt/min in HF TAC mice, P < 0.05) and it decreased pyruvate dehydrogenase phosphorylation. Cardiac fatty acid oxidation rates, AMPK^Tyr172 /ACC^Ser79 signalling and the acetylation of ß-oxidation enzymes, were attenuated following weight loss.

CONCLUSIONS

Weight loss is an effective intervention to improve cardiac function and energy metabolism in heart failure associated with obesity.

Impaired branched chain amino acid oxidation contributes to cardiac insulin resistance in heart failure

BACKGROUND

Branched chain amino acids (BCAA) can impair insulin signaling, and cardiac insulin resistance can occur in the failing heart. We, therefore, determined if cardiac BCAA accumulation occurs in patients with dilated cardiomyopathy (DCM), due to an impaired catabolism of BCAA, and if stimulating cardiac BCAA oxidation can improve cardiac function in mice with heart failure.

METHOD

For human cohorts of DCM and control, both male and female patients of ages between 22 and 66 years were recruited with informed consent from University of Alberta hospital. Left ventricular biopsies were obtained at the time of transplantation. Control biopsies were obtained from non-transplanted donor hearts without heart disease history. To determine if stimulating BCAA catabolism could lessen the severity of heart failure, C57BL/6J mice subjected to a transverse aortic constriction (TAC) were treated between 1 to 4-week post-surgery with either vehicle or a stimulator of BCAA oxidation (BT2, 40 mg/kg/day).

RESULT

Echocardiographic data showed a reduction in ejection fraction (54.3 ± 2.3 to 22.3 ± 2.2%) and an enhanced formation of cardiac fibrosis in DCM patients when compared to the control patients. Cardiac BCAA levels were dramatically elevated in left ventricular samples of patients with DCM. Hearts from DCM patients showed a blunted insulin signalling pathway, as indicated by an increase in P-IRS1ser636/639 and its upstream modulator P-p70S6K, but a decrease in its downstream modulators P-AKT ser473 and in P-GSK3β ser9. Cardiac BCAA oxidation in isolated working hearts was significantly enhanced by BT2, compared to vehicle, following either acute or chronic treatment. Treatment of TAC mice with BT2 significantly improved cardiac function in both sham and TAC mice (63.0 ± 1.8 and 56.9 ± 3.8% ejection fraction respectively). Furthermore, P-BCKDH and BCKDK expression was significantly decreased in the BT2 treated groups.

CONCLUSION

We conclude that impaired cardiac BCAA catabolism and insulin signaling occur in human heart failure, while enhancing BCAA oxidation can improve cardiac function in the failing mouse heart.

Allosteric, transcriptional and post-translational control of mitochondrial energy metabolism

The heart is the organ with highest energy turnover rate (per unit weight) in our body. The heart relies on its flexible and powerful catabolic capacity to continuously generate large amounts of ATP utilizing many energy substrates including fatty acids, carbohydrates (glucose and lactate), ketones and amino acids. The normal health mainly utilizes fatty acids (40-60%) and glucose (20-40%) for ATP production while ketones and amino acids have a minor contribution (10-15% and 1-2%, respectively). Mitochondrial oxidative phosphorylation is the major contributor to cardiac energy production (95%) while cytosolic glycolysis has a marginal contribution (5%). The heart can dramatically and swiftly switch between energy-producing pathways and/or alter the share from each of the energy substrates based on cardiac workload, availability of each energy substrate and neuronal and hormonal activity. The heart is equipped with a highly sophisticated and powerful mitochondrial machinery which synchronizes cardiac energy production from different substrates and orchestrates the rate of ATP production to accommodate its contractility demands. This review discusses mitochondrial cardiac energy metabolism and how it is regulated. This includes a discussion on the allosteric control of cardiac energy metabolism by short-chain coenzyme A esters, including malonyl CoA and its effect on cardiac metabolic preference. We also discuss the transcriptional level of energy regulation and its role in the maturation of cardiac metabolism after birth and cardiac adaptability for different metabolic conditions and energy demands. The role post-translational modifications, namely phosphorylation, acetylation, malonylation, succinylation and glutarylation, play in regulating mitochondrial energy metabolism is also discussed.