T. Dung Nguyen

Proteomic remodelling of mitochondrial oxidative pathways in pressure overload-induced heart failure

AIMS Impairment in mitochondrial energetics is a common observation in animal models of heart failure, the underlying mechanisms of which remain incompletely understood. It was our objective to investigate whether changes in mitochondrial protein levels may explain impairment in mitochondrial oxidative capacity in pressure overload-induced heart failure. METHODS AND RESULTS Twenty weeks following aortic constriction, Sprague-Dawley rats developed contractile dysfunction with clinical signs of heart failure. Comparative mitochondrial proteomics using label-free proteome expression analysis (LC-MS/MS) revealed decreased mitochondrial abundance of fatty acid oxidation proteins (six of 11 proteins detected), increased levels of pyruvate dehydrogenase subunits, and upregulation of two tricarboxylic acid cycle proteins. Regulation of mitochondrial electron transport chain subunits was variable, with downregulation of 53% of proteins and upregulation of 25% of proteins. Mitochondrial state 3 respiration was markedly decreased independent of the substrate used (palmitoyl-carnitine -65%, pyruvate -75%, glutamate -75%, dinitrophenol -82%; all P < 0.05), associated with impaired mitochondrial cristae morphology in failing hearts. Perfusion of isolated working failing hearts showed markedly reduced oleate (-68%; P < 0.05) and glucose oxidation (-64%; P < 0.05). CONCLUSION Pressure overload-induced heart failure is characterized by a substantial defect in cardiac oxidative capacity, at least in part due to a mitochondrial defect downstream of substrate-specific pathways. Numerous changes in mitochondrial protein levels have been detected, and the contribution of these to oxidative defects and impaired cardiac energetics in failing hearts is discussed.

Alterations in mitochondrial function in cardiac hypertrophy and heart failure

Normal cardiac function requires high and continuous supply with ATP. As mitochondria are the major source of ATP production, it is apparent that mitochondrial function and cardiac function need to be closely related to each other. When subjected to overload, the heart hypertrophies. Initially, the development of hypertrophy is a compensatory mechanism, and contractile function is maintained. However, when the heart is excessively and/or persistently stressed, cardiac function may deteriorate, leading to the onset of heart failure. There is considerable evidence that alterations in mitochondrial function are involved in the decompensation of cardiac hypertrophy. Here, we review metabolic changes occurring at the mitochondrial level during the development of cardiac hypertrophy and the transition to heart failure. We will focus on changes in mitochondrial substrate metabolism, the electron transport chain and the role of oxidative stress. We will demonstrate that, with respect to mitochondrial adaptations, a clear distinction between hypertrophy and heart failure cannot be made because most of the findings present in overt heart failure can already be found in the various stages of hypertrophy.

Glucagon-like peptide-1 reduces contractile function and fails to boost glucose utilization in normal hearts in the presence of fatty acids

UNLABELLED GLP-1 and exendin-4, which are used as insulin sensitizers or weight reducing drugs, were shown to improve glucose uptake in the heart. However, the direct effects of GLP-1 or exendin-4 on normal hearts in the presence of fatty acids, the main cardiac substrates, have never been investigated. We therefore assessed the effects of GLP-1 or exendin-4 on myocardial glucose uptake (GU), glucose oxidation (GO) and cardiac performance (CP) under conditions of fatty acid utilization. METHODS AND RESULTS Rat hearts were perfused with only glucose (5 mM) or glucose (5 mM) plus oleate (0.4 mM) as substrates for 60 min. After 30 min, GLP-1 or exendin-4 (0.5 nM or 5 nM) was added. In the absence of oleate, GLP-1 increased both GU and GO. Exendin-4 increased GO but showed no effect on GU. Neither GLP-1 nor exendin-4 affected CP. However, when oleate was present, GLP-1 failed to stimulate glucose utilization and exendin-4 even decreased GU. Furthermore, now GLP-1 reduced CP. In contrast to prior reports, this negative inotropic effect could not be blocked by the protein kinase A inhibitor H-89. We then measured myocardial GO and CP in rats receiving a 4-week GLP-1 infusion. Interestingly, this chronic treatment resulted in a significant reduction in both GO and CP. CONCLUSIONS Under the influence of oleate, GLP-1 reduces contractile function and fails to stimulate glucose utilization in normal hearts. Exendin-4 may acutely reduce cardiac glucose uptake but not contractility. We suggest advanced investigation of heart function and metabolism in patients treating with these peptides.

Triheptanoin Alleviates Ventricular Hypertrophy and Improves Myocardial Glucose Oxidation in Rats With Pressure Overload

OBJECTIVE Cardiac hypertrophy is characterized by changes in substrate utilization and activity of the Krebs cycle. We assessed the effects of triheptanoin, an odd-chain fat that might support the Krebs cycle, on cardiac metabolism and function in a model of cardiac hypertrophy. METHODS AND RESULTS Rats were subjected to aortic banding (AoB) to induce pressure overload (PO). Starting at 1 week after AoB, rats were blindly fed a control diet or a special diet containing triheptanoin at 7% (T7 group) or 30% (T30 group) of total energy value. Six weeks after AoB, echocardiography revealed attenuated hypertrophy and improved diastolic function of the left ventricle. Isolated working heart perfusion showed similar cardiac power, fatty acid oxidation, substrate preference, and insulin response among groups. However, cardiac glucose oxidation (GO) was increased in the T30 group compared with the T7 and control groups. Blood levels of the odd-chain ketone body beta-hydroxypentanoate confirmed adequate bioavailability of triheptanoin. Importantly, they were directly proportional to cardiac GO. CONCLUSIONS Treatment with triheptanoin-enriched diet reduces ventricular hypertrophy and improves diastolic function in rats with PO, which is associated with enhanced cardiac GO. The results suggest targeting supplementation of the Krebs cycle to approach ventricular and metabolic remodeling in cardiac hypertrophy.

GLP-1 Improves Diastolic Function and Survival in Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) has emerged as a public health burden with currently no effective medication. We assessed the treatment effects of the incretin hormone glucagon-like peptide-1 (GLP-1) on cardiac metabolism and function in a model of HFpEF. Following aortic banding, rats developed HFpEF characterized by diastolic dysfunction, pulmonary congestion, and poor survival (38%). A 4-week GLP-1 treatment via osmotic pumps significantly improved survival (70%) and reduced left ventricular stiffness, diastolic dysfunction, and pulmonary congestion. Isolated heart perfusion revealed preserved cardiac glucose oxidation (GO) and a shift in cardiac substrate utilization towards GO. While GLP-1 may boost insulin secretion and responsiveness, the protective effects were not related to cardiac insulin action. GLP-1 improves diastolic function and survival in rats with HFpEF, which was associated with a cardiac substrate switch towards GO. The therapeutic role of GLP-1 in HFpEF is new and warrants further investigation.

Chronic Perforation of the Aortic Arch by Kirschner Wires

Perforation of the heart or great vessels by orthopedic wires is a rare complication that mostly results in severe or even lethal organ injury. Therefore, such conditions mostly require immediate surgical removal of the wires. However, in some individual cases, a conservative approach may be preferable. We describe a case of a 70-year-old woman whose aortic arch has been penetrated by two Kirschner wires used for fixation of a right clavicle fracture 13 years ago. Notably, the complication was an incidental finding during computed tomography angiography for clarification of transient nonspecific neurological symptoms.

Letter to the Editor: GLP-1 and exendin-4: not simply two of a kind

to the editor: We read with great interest the recently published study by DeNicola et al. ([2][1]), entitled “Stimulation of glucagon-like peptide-1 receptor through exendin-4 preserves myocardial performance and prevents cardiac remodeling in infarcted myocardium”. The authors demonstrated