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International audience; SCOPE: Low-grade inflammation is a recognized hallmark of obesity. Endotoxins absorbed after high-fat meals have recently been implicated. Plasma lipopolysaccharides binding protein (LBP) and soluble cluster of differentiation 14 (sCD14) have also been suggested as clinical markers of endotoxemia. In mice, the ratio LBP/sCD14 has been associated with high fat diet induced inflammation. We tested the hypothesis that healthy subjects develop inflammation differently during weight gain according to changes of LBP/sCD14 ratio. METHODS AND RESULTS: Eighteen healthy men were overfed during 8 wk (+760 kcal/day). Endotoxemia, sCD14, LBP, and IL-6 were measured before and after overfeeding (OF) at fasting (n = 18) and postprandially (subcohort, n = 8). OF did not modify fasting IL-6 but increased the LBP/sCD14 ratio (P = 0.017). Subjects were categorized into tertiles for LBP/sCD14 ratio variation. Subjects in the highest tertile (+90% LBP/sCD14) increased plasma IL-6 (+26%) versus the lowest tertile due to a decrease of sCD14 associated with high LBP. The postprandial accumulation of endotoxins increased after OF (+160%). However, only four responding subjects presented increased postprandial IL-6 accumulation. CONCLUSION: OF increases postprandial endotoxemia but the inflammatory outcome may be modulated by endotoxin handling in plasma. This study supports a new concept whereby inflammation setup during the initial phase of weight gain is linked to the relative variations of LBP and sCD14.

Review; International audience; Mitochondria play a key role in the energy metabolism in skeletal muscle. A new concept has emerged suggesting that impaired mitochondrial oxidative capacity in skeletal muscle may be the underlying defect that causes insulin resistance. According to current knowledge, the causes and the underlying molecular mechanisms at the origin of decreased mitochondrial oxidative capacity in skeletal muscle still remain to be elucidated. The present review focuses on recent data investigating these issues in the area of metabolic disorders and describes the potential causes, mechanisms and consequences of mitochondrial dysfunction in the skeletal muscle.

Changes in eating habits, food composition and processing are involved in the “nutritional transition” that accompanied the obesity pandemic and the burst of metabolic diseases. This study is one of the first to describe the metabolic trajectories that differentiate the responses of overweight (OW) from lean individuals during weight gain. Nineteen lean and 19 OW male volunteers were submitted to moderate weight gain using a lipid-enriched overfeeding protocol designed to add about 3,300 kJ per day in excess to their usual diet. Metabolic explorations in combination with plasma and urine metabolomic profiles using liquid chromatography coupled with mass spectrometry were determined along 8 weeks to compare metabolic trajectories and determine early changes in metabolic processes after identification of specific early responding markers. Urinary metabolomic profiles during overfeeding evidenced differences in metabolic trajectories between groups, characterized by an increase over time of short-, medium-chain acylcarnitines, and bile acids in overweight subjects. For most of the anthropometric, metabolic parameters and plasma metabolomics data, the time-course evolution of all subjects was similar with distinction between groups. Plasma abundances of unsaturated lysophosphosphatidylcholine (22:6) decreased over time more importantly in normal weight subjects while most of those of the saturated species increased in both groups. These findings not evidenced with classical parameters, indicate a differential response to overfeeding in urine metabolomes of subjects, suggesting different nutrient metabolic fate with weight status. Subtle plasma and urine metabolic changes, mostly related to differences in the adaptation of β-oxidation and inflammation indicate a lower metabolic flexibility of OW subjects facing weight gain induced by overfeeding.

International audience; Context: The hypothesis of a limited expansion of sc adipose tissue during weight gain provides an attractive explanation for the reorientation of excess lipids toward ectopic sites, contributing to visceral adipose depots and metabolic syndrome. Objective: Our objective was to define whether the characteristics of sc adipose tissue influence the partition of lipids toward abdominal fat depots during weight gain in healthy men. Research Design and Methods: Forty-one healthy nonobese volunteers performed a 56-day over-feeding protocol (+760 kcal/d). Insulin sensitivity was estimated by euglycemic hyperinsulinemic clamp. Changes in abdominal visceral and sc adipose tissue depots were measured by magnetic resonance imaging. The fate of ingested lipids before and after overfeeding was investigated using a [d31]palmitate test meal, and gene expression was measured by real-time PCR in sc fat biopsies. Results: Overfeeding led to a 2.5-kg body weight increase with large interindividual variations in abdominal sc and visceral adipose tissues. There was no relationship between the relative expansions of these 2 depots, but the increase in visceral depot was positively associated with the magnitude of the postprandial exogenous fatty acid release in the circulation during the test meal. The regulation of lipid storage-related genes (DGAT2, SREBP1c, and CIDEA) was defective in the sc fat of the subjects exhibiting the largest accumulation in visceral depot. Conclusions: Characteristics of sc adipose tissue appear therefore to contribute to the development of visceral fat depot, supporting the adipose tissue expandability theory and extending it to early stages of weight gain in nonobese subjects. (J Clin Endocrinol Metab 98: 802-810, 2013)

International audience; Context: Deciphering the early processes occurring in adipose tissue during weight gain is a major issue for understanding the development of fat mass and obesity. Experimental overfeeding in humans is a unique situation to tackle these events. Objective: Our aim was to identify the pathways involved in sc adipose tissue remodeling during the initial phase of weight gain. Research Design and Methods: Forty-four healthy men were involved in an overfeeding protocol with a lipid-enriched diet (+ 760 kcal/d) for 2 months. Subcutaneous abdominal adipose tissue biopsies were taken for histology, transcriptomics, and Western blotting in the basal state, after 14 d, and at the end of the protocol. Results: Overfeeding significantly increased body weight (+ 2.5 kg) and fat mass. Reorganization of gene expression patterns occurred in adipose tissue with an up-regulation of numerous genes involved in lipid metabolism and storage, followed by clusters of genes related to angiogenesis and extracellular matrix remodeling. Histological examination showed increased microvascular density and connective tissue deposition after 56 d of overfeeding, with no changes in the number of macrophages or inflammatory cells. Inhibition of the canonical Wnt/beta-catenin signaling pathway and induction of the renin-angiotensin system might be implicated in the remodeling of sc adipose tissue. Conclusions: We characterize the coordinated and time-dependent processes that occur in human adipose tissue during the early phase of weight gain in healthy subjects and identify pathways representing potential targets in pathologies of adipose development, including obesity. (J Clin Endocrinol Metab 97: E183-E192, 2012)

Abdominal obesity is a major risk factor for muscle insulin resistance. Mitochondria may play a key role in this etiology.Changes in muscle mitochondrial content and function were examined according to abdominal obesity and insulin sensitivity in men.The descriptive MitHyCal study was conducted on the general population of Clermont-Ferrand, France.Forty-two healthy sedentary men (41.7 +/- 4.3 yr) were divided into four groups according to waist circumference: 87 cm or less (group 1, n = 10); 88-93 cm (group 2, n = 12); 94-101 cm (group 3, n = 10); and 102 cm or greater (group 4, n = 10).Plasma metabolic check-up was performed, and insulin sensitivity index was calculated from glucose and insulin responses to a 3-h oral glucose tolerance test. Muscle biopsies were obtained to assess mitochondrial content, oxidative phosphorylation activity, and superoxide anion (reactive oxygen species) production.Assessment of muscle mitochondrial content and function was planned before data collection began.Abdominal obesity was negatively correlated to insulin sensitivity index (r = -0.39; P0.01), and only group 4 was insulin-resistant (P0.05). There were no between-group differences in muscle mitochondrial content and maximal activity of key oxidative enzymes. In contrast, muscle mitochondrial ADP-stimulated respiration rate was 24% higher in groups 2 and 3 compared to groups 1 and 4 (P0.05). Mitochondrial ATP and reactive oxygen species production rates were 27 and 48% lower in group 4 than in group 1 (P0.05).Abdominal obesity is associated with alterations in intrinsic muscle mitochondrial function but not content. These adaptations mainly result in reduced mitochondrial ATP production rate in response to insulin resistance.

International audience; OBJECTIVE: Mitochondrial activity is altered in skeletal muscle of obese, insulin-resistant or type 2 diabetic patients. We hypothesized that this situation was associated with profound adaptations in resting muscle energetics. For that purpose, we used in vivo (31)P-nuclear magnetic resonance ((31)P-NMR) in male sedentary Wistar rats fed with obesogenic diets known to induce alterations in muscle mitochondrial activity. METHODS AND PROCEDURES: Two experimental diets (high sucrose and high fat) were provided for 6 weeks at two levels of energy (standard, N and high, H) and compared to control diet. The rates of the adenosine triphosphate (ATP) exchange between phosphocreatine (PCr) and gamma-ATP (k(a)) and beta-adenosine diphosphate (beta-ADP) to beta-ATP (k(b)) were evaluated using (31)P-NMR in resting gastrocnemius muscle. Muscle contents in phosphorylated compounds as well as creatine, were assessed using (31)P-NMR and biochemical assays, respectively. RESULTS: ATP content increased by 6.7-8.5% in standard-energy high-sucrose (NSU), high-energy high-fat (HF) and high-energy high-sucrose (HSU) groups compared to control (P < 0.05), whereas PCr content decreased by 4.2-6.4% (P < 0.01). Consequently, PCr to ATP ratio decreased in NSU, HF, and HSU groups, compared to control (P < 0.01). Furthermore in high-energy groups (HF and HSU) compared to control, creatine contents were decreased by 14-19% (P < 0.001), whereas k(a) and k(b) fluxes were increased by 89-133% (P < 0.001) and 243-277% (P < 0.01), respectively. DISCUSSION: Our in vivo data showed adaptations of resting skeletal muscle energetics in response to high-energy diets. Increased activity of enzymes catalyzing ATP production may reflect a compensatory mechanism to face impaired mitochondrial ATP synthesis in order to preserve intracellular energy homeostasis.

International audience; Mitochondrial dysfunction in skeletal muscle has been implicated in the development of type 2 diabetes. However, whether these changes are a cause or a consequence of insulin resistance is not clear. We investigated the structure and function of muscle mitochondria during the development of insulin resistance and progression to diabetes in mice fed a high-fat, high-sucrose diet. Although 1 month of high-fat, high-sucrose diet feeding was sufficient to induce glucose intolerance, mice showed no evidence of mitochondrial dysfunction at this stage. However, an extended diet intervention induced a diabetic state in which we observed altered mitochondrial biogenesis, structure, and function in muscle tissue. We assessed the role of oxidative stress in the development of these mitochondrial abnormalities and found that diet-induced diabetic mice had an increase in ROS production in skeletal muscle. In addition, ROS production was associated with mitochondrial alterations in the muscle of hyperglycemic streptozotocin-treated mice, and normalization of glycemia or antioxidant treatment decreased muscle ROS production and restored mitochondrial integrity. Glucose- or lipid-induced ROS production resulted in mitochondrial alterations in muscle cells in vitro, and these effects were blocked by antioxidant treatment. These data suggest that mitochondrial alterations do not precede the onset of insulin resistance and result from increased ROS production in muscle in diet-induced diabetic mice.

National audience

Objective: Obesity and insulin resistance are associated with muscle mitochondrial dysfunction, which might be related to impairment of mitochondrial protein synthesis. This study aimed at investigating mixed and mitochondrial protein synthesis in skeletal muscle in response to dietary manipulations. Research Methods and Procedures: High-sucrose (SU) and high-fat, high-sucrose (F) diets were provided for 6 weeks to Wistar rats at standard (N) and high (H) energy intakes and compared with controls. Fractional synthesis rates of mixed (FSRPT) and mitochondrial (FSRm) proteins within the oxidative (soleus) and glycolytic (tibialis) muscles were measured using stable isotope flooding dose technique using l-[13C]-valine. Carbonyl content, citrate synthase, and cytochrome c oxidase activities were assayed spectrophotometrically on isolated mitochondria. Results: In the soleus, FSRPT was increased by 40% in the NSU and NF groups and by 65% in the HSU and HF groups (p < 0.001 vs. control). FSRm was increased with high-fat diets (NF, +16%; HF, +32%; p < 0.01). In the tibialis, FSRPT was enhanced in all experimental groups (+31% to 37%, p < 0.05 vs. control). FSRm was augmented in the NSU, NF, and HF groups (+28% to 32%, p < 0.01). Cytochrome c oxidase activity was significantly decreased in all experimental groups in the soleus (p < 0.001). Discussion: Muscle mixed and mitochondrial protein FSR are enhanced after short-term dietary intervention known to induce insulin resistance and obesity. Adaptations are muscle type specific and may not explain alterations in mitochondrial oxidative capacity but might contribute to maintain mitochondrial functioning.

International audience; OBJECTIVE: Mitochondrial dysfunction might predispose individuals to develop insulin resistance. Our objective was to determine whether mitochondrial dysfunction or insulin resistance was the primary event during high-fat (HF) diet. RESEARCH METHODS AND PROCEDURES: Rats were fed an HF diet for 0, 3, 6, 9, 14, 20, or 40 days and compared with control. Soleus and tibialis muscle mitochondrial activity were assessed using permeabilized fiber technique. Insulin [area under the curve for insulin (AUC(I))] and glucose [area under the curve for glucose (AUC(G))] responses to intraperitoneal glucose tolerance test as well as fasting plasma non-esterified fatty acids (NEFAs), triglyceride, and glycerol concentrations were determined. RESULTS: AUC(I) and AUC(G) were altered from Day 6 (p < 0.01 vs. Day 0). In soleus, oxidative phosphorylation (OXPHOS) activity was transiently enhanced by 26% after 14 days of HF diet (p < 0.05 vs. Day 0) conjointly with 62% increase in NEFA concentration (p < 0.05 vs. Day 0). This was associated with normalized AUC(G) at Day 14 and with a decline of plasma NEFA concentration together with stabilization of intra-abdominal adiposity at Day 20. Prolongation of HF diet again caused an increase in plasma NEFA concentration, intra-abdominal adiposity, AUC(I), and AUC(G). At Day 40, significant decrease in OXPHOS activity was observed in soleus. DISCUSSION: Mitochondria first adapt to overfeeding in oxidative muscle limiting excess fat deposition. This potentially contributes to maintain glucose homeostasis. Persistent overfeeding causes insulin resistance and results in a slow decline in oxidative muscle OXPHOS activity. This shows that the involvement of mitochondria in the predisposition to insulin resistance is mainly due to an inability to face prolonged excess fat delivery.

International audience; The relationship between iron and insulin-resistance (IR) is documented by the positive correlation between iron stores and IR. Moreover, some patients exhibited a hepatic iron overload associated with IR (HIO-IR) but the mechanism involved in this overload is not known. Thus, we studied the iron metabolism disturbances in an animal model of IR and the influence of provoked hyperglycemia/hyperinsulinemia on plasma iron parameters. Wistar rats were fed a control or a high-fat/high-energy (HF/HE) diet. Plasma glucose, insulin, iron, transferrin and transferrin saturation (TS) were measured during intra-peritoneal glucose test tolerance (IPGTT) compared to saline. Hemogram, tissue iron concentrations and hepatic hepcidin mRNA expression were determined at the end of experiment. HF/HE rats exhibited higher body and liver weights, increased IR-index and hemoglobin concentration. Iron content was lower in the spleen of HF/HE rats and tended to decrease in the liver as compared to controls. Transferrin values were higher and these of TS lower in HF/HE group. The hepcidin mRNA was 3.5-fold lower in HF/HE rats than in controls. IPGTT had no effect on iron status parameters in both groups. As reflected by higher hemoglobin concentration, IR could increase erythropoïesis which enhances iron requirement. Iron stores and TS value decreased leading to a down-regulation of hepcidin expression which increased iron absorption. Hepcidin expression should be investigated in metabolic syndrome and hepatic iron overload associated with IR.

International audience; Caloric restriction (CR) delays the onset of age-related mitochondrial abnormalities but does not prevent the decline in ATP production needed to sustain muscle protein fractional synthesis rate (FSR) and contractile activity. We hypothesized that improving mitochondrial activity and FSR using a CR diet with maintained protein intakes could enhance myofibrillar protein FSR and consequently improve muscle strength in aging rats. Wistar rats (21 months old) were fed either an ad libitum (AL), 40% protein-energy restricted (PER) or 40% AL-isonitrogenous energy restricted (ER) diet for 5 months. ATP production, electron transport chain activity, reactive oxygen species (ROS) generation, protein carbonyl content and FSR were determined in both tibialis anterior (TA) and soleus muscle mitochondria. Myosin and actin FSR and grip force were also investigated. The ER diet led to improved mitochondrial activity and ATP production in the TA and soleus muscles in comparison with PER. Furthermore, mitochondrial FSR in the TA was enhanced under the ER diet but diminished under the PER. Mitochondrial protein carbonyl content was decreased by both the ER and PER diets. The ER diet was able to improve myosin and actin FSR and grip force. Therefore, the synergistic effects of CR with maintained protein intake may help to limit the progression of sarcopenia by optimizing the turnover rates and functions of major proteins in skeletal muscle.

International audience

644; International audience

Introduction Des dysfonctionnements mitochondriaux dans le muscle squelettique seraient impliques dans le developpement du diabete de type 2. Cependant, si ces alterations sont une cause ou une consequence de l’insulino-resistance n’est toujours pas determine. Materiels et methodes Nous avons donc etudie la structure et les fonctions mitochondriales au cours du developpement de l’insulino-resistance, induite chez l’animal par une diete riche en lipides et en sucrose. Resultats Aucune alteration mitochondriale n’est mis en evidence dans le muscle de souris prediabetiques, alors que la biogenese, la structure et les fonctions mitochondriales sont alterees dans le muscle de souris diabetiques. D’autre part, nous demontrons que le stress oxydant musculaire est un element causal majeur dans ces alterations mitochondriales puisque 1. il existe une augmentation de la production locale de radicaux libres (RL) uniquement dans le muscle squelettique de souris diabetiques, associee a une hyperglycemie et hyperlipidemie, 2. Une production de RL est egalement associee a des alterations mitochondriales dans le muscle de souris de souris rendues hyperglycemiques par un traitement a la streptozotocine, 3. Chez ces souris, la normalisation de la glycemie par un traitement a l’insuline ou a la phlorizine, ainsi qu’un traitement antioxydant, diminuent la production de RL et restaurent les alterations mitochondriales, et 4. l’induction d’une production de RL par du glucose ou des lipides, in vitro, altere la densite et les fonctions mitochondriales dans des cellules musculaires en culture, et ces effets sont restaures par un traitement antioxydant. Conclusion L’ensemble de ces donnees suggerent que les alterations mitochondriales ne sont pas causales dans le developpement de l’insulino-resistance, mais plutot la consequence d’un stress oxydant musculaires associe a l’hyperglycemie et l’hyperlipidemie des souris diabetiques.

Introduction Une reduction des fonctions oxydatives mitochondriales est frequemment observee dans le muscle de patients insulinoresistants, obeses ou diabetiques de type 2. Mais dans la plupart des etudes existantes, la fonction mitochondriale est evaluee independamment de l'activite physique et lorsque l'obesite ou le diabete est deja diagnostique. Le but de notre travail etait d'observer les changements de la fonction mitochondriale musculaire en fonction du tour de taille (TT) chez l'homme sedentaire. Materiels et methodes Soixante hommes (35-50 ans) ont ete repartis en 5 groupes en fonction du TT : 115 cm (G5 n=5). Le comportement sedentaire a ete valide par un questionnaire d'activite (Baecke) et un test d'effort sur velo. Chaque sujet a ete caracterise par un bilan metabolique : bilan plasmatique, test de tolerance au glucose, composition corporelle et fonction mitochondriale (fibres musculaires permeabilisees a partir d'une biopsie du vastus lateralis ). Observation Seuls les sujets obeses (G5) presentent un dysfunctionnement mitochondrial alors que le sensibilite a l'insuline est significativement diminuee (G4 et G5). Les groupes intermediaires (G2 et G3) presentent une respiration mitochondriale dans le muscle plus elevee que dans les groupes extremes (minces G1 et obeses G4 et G5). Une correlation negative existe entre l'obesite abdominale et la production mitochondriale d'ATP et d'especes reactives de l'oxygene dans le muscle. Discussion Ce travail suggere que l'adaptation de l'activite mitochondriale musculaire en situation de surpoids pourrait contribuer a limiter les complications metaboliques associees mais jusqu'a un certain stade d'obesite abdominale. L'expression de genes cles impliques dans le controle des fonctions mitochondriales est en cours d'investigation (RT-PCR). Conclusion Il n'existe pas de relation lineaire entre l'obesite abdominale et la capacite oxydative mitochondriale musculaire chez l'homme sedentaire.

Introduction et but de l’etude L’insuffisance cardiaque evolue dans 16% des cas vers un etat de denutrition caracterise par une perte importante du muscle squelettique, appelee cachexie cardiaque. La cachexie cardiaque pourrait faire intervenir de profondes modifications du metabolisme proteique, ainsi que des perturbations des fonctions mitochondriales au sein du muscle. Notre but etait donc d’etudier la proteosynthese et les fonctions mitochondriales de differents types musculaires (squelettiques types 1 et 2, cardiaque) durant la cachexie cardiaque chez le rat. Materiel et methodes Un infarctus du myocarde (IDM) a ete realise chez 7 rats LEWIS de 3 mois par ligature chirurgicale de l’IVA. La dysfonction ventriculaire gauche etait confirmee par echocardiographie. Un animal ayant maigri de plus de 7,5% etait considere comme cachectique cardiaque (CC) et etait alors sacrifie simultanement a un rat temoin sain (TS). Apres l’injection d’un traceur isotopique ([13C]valine), le sang, les muscles (soleus, gastrocnemius, tibialis anterior), le coeur, le foie et le tissu adipeux intra-abdominal etaient preleves. Le taux de synthese (FSR) des proteines mitochondriales etait calcule a partir de l’enrichissement en [13C]valine des proteines mesure par spectrometrie de masse. Les activites enzymatiques mitochondriales de la citrate synthase (CS) et de la cytochrome c oxydase (COX) etaient mesurees par spectrophotometrie. L’analyse statistique utilisait un test non parametrique de Mann-Withney. Resultats 6 rats sur les 7 ayant subi l’IDM sont devenus cachectiques, en moyenne en 85 jours. Le poids du foie etait statistiquement superieur dans le groupe CC par rapport aux TS (11,4±2,4 g vs 8,6±1,3 g, P Conclusions Cette etude confirme que la CC est associee a de profondes alterations de la fonction mitochondriale musculaire dans les muscles squelettiques de type oxydatif (soleus), associees a une augmentation de la vitesse de synthese des proteines de cet organite. Ce dernier phenomene pourrait etre lie a des mecanismes de compensation tentant de limiter les perturbations fonctionnelles.

Poster P10; International audience

Supplemental Material can be found at: http://jn.nutrition.org/cgi/content/full/136/8/2194/DC1; International audience; Obesity is often associated with insulin resistance and mitochondrial dysfunction within skeletal muscles, but the causative factors are not clearly identified. The present study examined the role of nutrition, both qualitatively and quantitatively, in the induction of muscle mitochondrial defects. Two experimental diets [high sucrose (SU) and high fat (F)] were provided for 6 wk to male Wistar rats at 2 levels of energy [standard (N) and high (H)] and compared with a standard energy cornstarch-based diet (C). Insulin sensitivity (intraperitoneal glucose tolerance test, IPGTT) and intramyocellular triglyceride (IMTG) content (H-1 MRS) were determined at wk 5. Mitochondrial oxidative phosphorylation and superoxide anion radical (MSR) production were assessed on soleus (oxidative) and tibialis (glycolytic) muscles. Experimental diets induced hyperinsulinemia during IPGTT (P < 0.01 vs. C). Rats in the HSU and HF groups were hyperglycemic relative to the C group, P < 0.05 vs. C. The severity of insulin resistance paralleled IMTG accumulation (P < 0.05). In soleus, mitochondrial respiration and ATP production rates were lower in HSU and HF than in C (P < 0.05). By contrast, respiration was unaffected by the diets in tibialis, whereas ATP production tended to be lower in rats fed the experimental diets compared with C (P = 0.09). Mitochondrial adaptations were associated with more than a 50% reduction in MSR production in HSU and HF compared with C in both soleus (P < 0.05) and tibialis (P < 0.01). Changes in mitochondrial functions in the NSU and NF groups were intermediate and not significantly different from C. Therefore, excess fat or sucrose and more importantly, excess energy intake by rats is associated with muscle type-specific mitochondrial adaptations, which contribute to decrease mitochondrial production of ATP and reactive oxygen species.