Impact of obesity on day-night differences in cardiac metabolism

An intrinsic property of the heart is an ability to rapidly and coordinately adjust flux through metabolic pathways in response to physiologic stimuli (termed metabolic flexibility). Cardiac metabolism also fluctuates across the 24-hours day, in association with diurnal sleep-wake and fasting-feeding cycles. Although loss of metabolic flexibility has been proposed to play a causal role in the pathogenesis of cardiac disease, it is currently unknown whether day-night variations in cardiac metabolism are altered during disease states. Here, we tested the hypothesis that diet-induced obesity disrupts cardiac diurnal metabolic flexibility , which is normalized by time-of-day-restricted feeding. Chronic high fat feeding (20-wk)-induced obesity in mice, abolished diurnal rhythms in whole body metabolic flexibility, and increased markers of adverse cardiac remodeling (hypertrophy, fibrosis, and steatosis). RNAseq analysis revealed that 24-hours rhythms in the cardiac transcriptome were dramatically altered during obesity; only 22% of rhythmic transcripts in control hearts were unaffected by obesity. However, day-night differences in cardiac substrate oxidation were essentially identical in control and high fat fed mice. In contrast, day-night differences in both cardiac triglyceride synthesis and lipidome were abolished during obesity. Next, a subset of obese mice (induced by 18-wks ad libitum high fat feeding) were allowed access to the high fat diet only during the 12-hours dark (active) phase, for a 2-wk period. Dark phase restricted feeding partially restored whole body metabolic flexibility, as well as day-night differences in cardiac triglyceride synthesis and lipidome. Moreover, this intervention partially reversed adverse cardiac remodeling in obese mice. Collectively, these studies reveal diurnal metabolic inflexibility of the heart during obesity specifically for nonoxidative lipid metabolism (but not for substrate oxidation), and that restricting food intake to the active period partially reverses obesity-induced cardiac lipid metabolism abnormalities and adverse remodeling of the heart

Mesure du rapport 13c/12c de métabolites d'androgènes et de pregnènolone administrés par voie orale : une étude comparative interlaboratoire

La transcription des symboles et des caractères spéciaux utilisés dans la version originale de ce résumé n’a pas été possible en raison de limitations techniques. La version correcte de ce résumé peut être lue en PDF. Le contrôle du dopage sportif par les stéroïdes pouvant potentiellement se retrouver dans le corps humain de façon naturelle est très compliqué. En effet, les concentrations de ces stéroïdes peuvent varier naturellement de façon substantielle d'un individu à l'autre rendant difficile l'utilisation d'une fourchette de valeurs normales à des fins de référence. De plus, la méthode de dépistage par chromatographie en phase gazeuse et spectrométrie de masse (CG/SM) ne permet pas de différencier l'origine endogène ou exogène d'un stéroïde urinaire. C'est ici qu'entre en jeu la méthode de confirmation par la spectrométrie de masse des rapports isotopiques (CG/C/SMRI). Cette méthode, dont l'utilisation dans le domaine du contrôle de dopage sportif a été proposée en 1994, permet la différenciation des stéroïdes de sources endogène et exogène par l'analyse de leur teneur en carbone 13, isotope naturel du carbone (12C) Une première partie du projet était de vérifier la possibilité d'analyser des norstéroïdes par CG/C/SMRI. Cette analyse est limitée due aux très petites concentrations des métabolites norandrostérone (NA) et norétiocholanolone (NE) d'origine endogène retrouvées parfois dans les urines. Afin de vérifier la sensibilité de notre méthode, nous avons utilisé les urines recueillies dans le cadre d'une étude d'excrétion réalisée avec une crème à base de norandrostènedione et de norandrostènediol vendue commercialement aux États-Unis. Bien que nous ayons réussi à identifier les pics correspondants à la NA et la NE exogènes, la méthode utilisée ne nous donne pas la sensibilité requise pour l'analyse de traces. Le même problème de sensibilité est rencontré lors des analyses de rapports isotopiques de la testostérone urinaire. Généralement, sa concentration dans l'urine est trop faible pour être analysée directement par CG/C/SMRI. Nous avons comparé différentes méthodes permettant 1'isolement et la séparation par chromatographie liquide de la testostérone et de 1'épitestostérone, deux ep1meres non résolus chromatographiquement en l'absence de dérivation chimique. La méthode retenue nous permet une bonne séparation des deux stéroïdes. Le but principal du projet était de vérifier la validité de la méthode de détection de stéroïdes exogènes en réalisant une étude comparative entre trois laboratoires accrédités par L’AMA. Ces trois laboratoires, situés à Tokyo, Japon, à Cologne, Allemagne, et à Montréal, Canada, ont une longue expérience en contrôle de dopage sportif et ont chacun développé leur propre méthode de préparation des échantillons pour les analyses de rapports isotopiques. Pour réaliser 1'étude, les trois laboratoires se sont partagés des échantillons urinaires provenant de diverses études d'excrétion. Les stéroïdes étudiés lors de ces travaux sont la testostérone, la DHEA, l'androstènedione et la pregnènolone. Les résultats obtenus par les trois laboratoires sont comparés dans ce rapport non seulement en terme de valeurs absolues, mais surtout en terme de différence entre les valeurs des rapports 13C/12C des métabolites et celles des stéroïdes de référence. Ce critère est celui qui a été retenu par l'Agence mondiale antidopage afin de limiter les variations retrouvées entre les laboratoires et les variations interindividuelles. Ainsi, pour toutes les études d'excrétion, les trois laboratoires ont obtenu des résultats concordants malgré les protocoles différents, démontrant ainsi l'application universelle de la CG/C/SMRI à des fins de confirmation de 1'administration de testostérone et ses précurseurs

Reducing 14-3-3ζ expression influences adipocyte maturity and impairs function

One of the primary metabolic functions of a mature adipocyte is to supply energy via lipolysis, or the catabolism of stored lipids. Adipose triacylglycerol lipase (ATGL) and hormone-sensitive lipase (HSL) are critical lipolytic enzymes, and their phosphorylation generates phospho-binding sites for 14-3-3 proteins, a ubiquitously expressed family of molecular scaffolds. Although we previously identified essential roles of the 14-3-3ζ isoform in murine adipogenesis, the presence of 14-3-3 protein binding sites on ATGL and HSL suggests that 14-3-3ζ could also influence mature adipocyte processes like lipolysis. Here we demonstrate that 14-3-3ζ is necessary for lipolysis in male mice and fully differentiated 3T3-L1 adipocytes, as depletion of 14-3-3ζ significantly impaired glycerol and free fatty acid (FFA) release. Unexpectedly, reducing 14-3-3ζ expression was found to significantly impact adipocyte maturity, as observed by reduced abundance of peroxisome proliferator-activated receptor (PPAR)γ2 protein and expression of mature adipocyte genes and those associated with de novo triglyceride synthesis and lipolysis. The impact of 14-3-3ζ depletion on adipocyte maturity was further examined with untargeted lipidomics, which revealed that reductions in 14-3-3ζ abundance promoted the acquisition of a lipidomic signature that resembled undifferentiated preadipocytes. Collectively, these findings reveal a novel aspect of 14-3-3ζ in adipocytes, as reducing 14-3-3ζ was found to have a negative effect on adipocyte maturity and adipocyte-specific processes like lipolysis. </jats:p

Reducing 14-3-3ζ expression influences adipocyte maturity and impairs function

AbstractOne of the primary metabolic functions of a mature adipocyte is to supply energy via lipolysis, or the catabolism of stored lipids. Hormone-sensitive lipase (HSL) is a critical lipolytic enzyme, and its phosphorylation and subsequent activation by PKA generates phospho-binding sites for 14-3-3 proteins, a ubiquitously expressed family of molecular scaffolds. While we previously identified essential roles of the 14-3-3ζ isoform in murine adipogenesis, the presence of 14-3-3 protein binding sites on HSL suggests that 14-3-3ζ could also influence mature adipocyte processes like lipolysis. Herein, we demonstrate that 14-3-3ζ is necessary for lipolysis in male mice and fully differentiated 3T3-L1 adipocytes, as depletion of 14-3-3ζ significantly impaired glycerol and FFA release. Unexpectedly, this was not due to impairments in signaling events underlying lipolysis; instead, reducing 14-3-3ζ expression was found to significantly impact adipocyte maturity, as observed by reduced abundance of PPARγ2 protein and expression of mature adipocytes genes and those associated withde novotriglyceride synthesis and lipolysis. The impact of 14-3-3ζ depletion on adipocyte maturity was further examined with untargeted lipidomics, which revealed that reductions in 14-3-3ζ abundance promoted the acquisition of a lipidomic signature that resembled undifferentiated, pre-adipocytes. Collectively, these findings reveal a novel aspect of 14-3-3ζ in adipocytes, as reducing 14-3-3ζ was found to have a negative effect on adipocyte maturity and adipocyte-specific processes like lipolysis.</jats:p

Metabolic Response of the Immature Right Ventricle to Acute Pressure Overloading

Background Surgical palliation or repair of complex congenital heart disease in early infancy can produce right ventricular ( RV ) pressure overload, often leading to acute hemodynamic decompensation. The mechanisms causing this acute RV dysfunction remain unclear. We tested the hypothesis that the immature right ventricle lacks the ability to modify substrate metabolism in order to meet increased energy demands induced by acute pressure overloading. Methods and Results Twenty‐two infant male mixed breed Yorkshire piglets were randomized to a sham operation (Control) or pulmonary artery banding yielding &gt;2‐fold elevation over baseline RV systolic pressure. We used carbon 13 ( 13 C)‐labeled substrates and proton nuclear magnetic resonance to assess RV energy metabolism. [Phosphocreatine]/[ ATP ] was significantly lower after pulmonary artery banding. [Phosphocreatine]/[ ATP ] inversely correlated with energy demand indexed by maximal sustained RV systolic pressure/left ventricular systolic pressure. Fractional contributions of fatty acids to citric acid cycle were significantly lower in the pulmonary artery banding group than in the Control group (medium‐chain fatty acids; 14.5±1.6 versus 8.2±1.0%, long‐chain fatty acids; 9.3±1.5 versus 5.1±1.1%). 13 C‐flux analysis showed that flux via pyruvate decarboxylation did not increase during RV pressure overloading. Conclusions Acute RV pressure overload yielded a decrease in [phosphocreatine]/[ ATP ] ratio, implying that ATP production did not balance the increasing ATP requirement. Relative fatty acids oxidation decreased without a reciprocal increase in pyruvate decarboxylation. The data imply that RV inability to adjust substrate oxidation contributes to energy imbalance, and potentially to contractile failure. The data suggest that interventions directed at increasing RV pyruvate decarboxylation flux could ameliorate contractile dysfunction associated with acute pressure overloading. </jats:sec

Metabolic Response to Stress by the Immature Right Ventricle Exposed to Chronic Pressure Overload

Background The right ventricle exposed to chronic pressure overload exhibits hypertrophy and decompensates when exposed to stress. We hypothesize that impaired ability to increase myocardial oxidative flux through pyruvate dehydrogenase leads to hypertrophied right ventricular ( RV ) dysfunction when exposed to hemodynamic stress, and pyruvate dehydrogenase stimulation can improve RV function. Methods and Results Infant male Yorkshire piglets (13.5±0.6 kg weight, n=19) were used to assess substrate fractional contribution to the citric acid cycle after sustained pulmonary artery banding ( PAB ). Carbon 13–labeled glucose, lactate, and leucine, oxidative substrate tracers for the citric acid cycle, were infused into the right coronary artery on 7 to 10 days after PAB . RV systolic pressure, RV free wall thickness, and individual cardiomyocyte cell size after PAB were significantly elevated compared with the sham group. Both fractional glucose and lactate oxidations in the PAB group were &gt;2‐fold higher than in the sham group. Pigs with overdrive atrial pacing (≈80% increase in heart rate) stress after PAB showed only a 22% increase in rate‐pressure product from baseline before atrial pacing and limited carbohydrate oxidation rate in the right ventricle. Intracoronary infusion of dichloroacetate, a pyruvate dehydrogenase agonist, produced higher rate‐pressure product (59% increase) in response to increased workload by atrial pacing in association with a marked increase in lactate oxidation. Conclusions The immature hypertrophied right ventricle shows limited ability to increase carbohydrate oxidation in response to tachycardia stress leading to energy supply/utilization imbalance and decreased systolic function. Enhanced pyruvate dehydrogenase activation by dichloroacetate increases energy supply and preserves hypertrophied RV contractile function during hemodynamic stress. </jats:sec