Rôle et mécanisme d'action de la metformine et du telmisartan sur la régulation de la prise alimentaire

Dans ce travail de thèse, nous avons étudié les mécanismes d'action de deux médicaments connus pour diminuer la prise alimentaire et pondérale : la metformine et le telmisartan. Nous avons dans un premier temps étudié les effets de la metformine, un antidiabétique oral connu pour avoir des effets anorexigènes. Les mécanismes hypothalamiques potentiellement impliqués dans la modulation de la prise alimentaire par la metformine ont été étudiés dans trois groupes de rats : un groupe de rats obèses (DIO), un groupe de rats résistants à l'obésité (DR) ainsi qu'un groupe contrôle. A la fin de la période de prise pondérale de six mois, les rats DIO avaient des taux d'ARNm de NPY hypothalamique plus élevés que leurs congénères résistants et contrôles. Chez les DIO ainsi que chez les DR un traitement par metformine induit une baisse significative de la prise alimentaire accompagnée par une baisse du poids. Nous avons pu d'autre part constater que la perte de poids obtenue par un traitement de metformine était corrélée aux taux circulants de leptine avant le traitement. Cet effet s'accompagne d'une augmentation de l'expression du récepteur ObRb au niveau hypothalamique. Dans un second temps, nous avons étudié les effets du telmisartan, un inhibiteur du récepteur à l'angiotensine II ayant une activité agoniste partielle PPARγ. L'influence du telmisartan associé à la pioglitazone sur la prise alimentaire et pondérale a été examinée en étudiant leur effet sur les neuropeptides hypothalamiques responsables du contrôle de la prise alimentaire. Quatre groupes de souris soumises à un régime riche en graisse ont été formés : un groupe placebo, un groupe pioglitazone, un groupe telmisartan et un groupe pioglitazone-telmisartan. Le telmisartan a aboli la prise pondérale induite par une diète riche en graisse ou par un traitement de pioglitazone. Cette diminution était corrélée à une baisse de la prise alimentaire et de l'expression hypothalamique d'AgRP. Cette étude confirme donc les effets anorexigènes du telmisartan et démontre pour la première fois le rôle fonctionnel du telmisartan sur l'expression hypothalamique d'AgRP. English Abstract : In this work, we investigated the effect of two drugs known to have interessants effects on food intake and body weight. First we investigated the hypothalamic mechanisms potentially implicated in the modulation of feeding by the glucose-lowering drug metformin in three different groups of animals: diet-induced obese (DIO) and diet-resistant (DR) male rats as well as lean controls (CT). At the end of the high fat diet period, despite higher leptin levels, DIO rats had higher levels of hypothalamic NPY expression than DR or CT, suggesting a central leptin resistance. In DIO but also in DR rats, metformin treatment induced significant reductions of food intake accompanied by decreases in body weight. Interestingly, the weight loss achieved by metformin was correlated with pre-treatment plasma leptin levels. This effect was paralleled by a stimulation of the expression of the leptin receptor gene (ObRb) in the arcuate nucleus. Next we investigated the antihypertensive drug Telmisartan, an angiotensin II receptor blocker with PPARγ agonistic properties. The influence of telmisartan, of pioglitazone and of their association on weight gain and food intake was assessed by studying their effects on neuro-endocrine mediators involved in food intake. Mice were fed a high fat diet, weightmatched and randomized in four treatment groups: vehicle, pioglitazone, telmisartan and pioglitazone-telmisartan. Telmisartan treatment was found to abolish weight and fat gain in either vehicle or pioglitazone treated mice. This effect was accompanied by a decrease in food intake. The hypothalamic expression of the agouti-related protein and plasma leptin levels show also a decrease under metformin treatment. This study confirms the anorexigenic effects of telmisartan in mice fed a high fat diet, and suggests for the first time a functional role of telmisartan on hypothalamic orexigenic agouti-related protein regulation.

In Vivo Modulation of Mitochondrial Activity Determines HSC Engraftment and Post-Transplant Survival in Mice

Cellular metabolism is emerging as a potential fate determinant in cancer and stem cell biology, constituting a crucial regulator of the hematopoietic stem cell (HSC) pool [1-4]. The extremely low oxygen tension in the HSC microenvironment of the adult bone marrow forces HSCs into a low metabolic profile that is thought to enable their maintenance by protecting them from reactive oxygen species (ROS). Although HSC quiescence has for long been associated with low mitochondrial activity, as testified by the low rhodamine stain that marks primitive HSCs, we hypothesized that mitochondrial activation could be an HSC fate determinant in its own right. We thus set to investigate the implications of pharmacologically modulating mitochondrial activity during bone marrow transplantation, and have found that forcing mitochondrial activation in the post-transplant period dramatically increases survival. Specifically, we examined the mitochondrial content and activation profile of each murine hematopoietic stem and progenitor compartment. Long-term-HSCs (LT-HSC, Lin-cKit+Sca1+ (LKS) CD150+CD34-), short-term-HSCs (ST-HSC, LKS+150+34+), multipotent progenitors (MPPs, LKS+150-) and committed progenitors (PROG, Lin-cKit+Sca1-) display distinct mitochondrial profiles, with both mitochondrial content and activity increasing with differentiation. Indeed, we found that overall function of the hematopoietic progenitor and stem cell compartment can be resolved by mitochondrial activity alone, as illustrated by the fact that low mitochondrial activity LKS cells (TMRM low) can provide efficient long-term engraftment, while high mitochondrial activity LKS cells (TMRM high) cannot engraft in lethally irradiated mice. Moreover, low mitochondrial activity can equally predict efficiency of engraftment within the LT-HSC and ST-HSC compartments, opening the field to a novel method of discriminating a population of transitioning ST-HSCs that retain long-term engraftment capacity. Based on previous experience that a high-fat bone marrow microenvironment depletes short-term hematopoietic progenitors while conserving their long-term counterparts [5], we set to measure HSC mitochondrial activation in high-fat diet fed mice, known to decrease metabolic rate on a per cell basis through excess insulin/IGF-1 production. Congruently, we found lower mitochondrial activation as assessed by flow cytometry and RT-PCR analysis as well as a depletion of the short-term progenitor compartment in high fat versus control chow diet fed mice. We then tested the effects of a mitochondrial activator known to counteract the negative effects of high fat diet. We first analyzed the in vitro effect on HSC cell cycle kinetics, where no significant change in proliferation or division time was found. However, HSCs responded to the mitochondrial activator by increasing asynchrony, a behavior that is thought to directly correlate with asymmetric division [6]. As opposed to high-fat diet fed mice, mice fed with the mitochondrial activator showed an increase in ST-HSCs, while all the other hematopoietic compartments were comparable to mice fed on control diet. Given the dependency on short-term progenitors to rapidly reconstitute hematopoiesis following bone marrow transplantation, we tested the effect of pharmacological mitochondrial activation on the recovery of mice transplanted with a limiting HSC dose. Survival 3 weeks post-transplant was 80% in the treated group compared to 0% in the control group, as predicted by faster recovery of platelet and neutrophil counts. In conclusion, we have found that mitochondrial activation regulates the long-term to short-term HSC transition, unraveling mitochondrial modulation as a valuable drug target for post-transplant therapy. Identification of molecular pathways accountable for the metabolically mediated fate switch is currently ongoing.

Metabolic effects of fructose in humans

Abstract : Fructose is a simple sugar, whose consumption has increased over the past decades. In rodents, a high-fructose diet (HFrD) induces several features of the metabolic syndrome. The aim of the studies included in this thesis was to investigate the metabolic effects of a HFrD in humans, with a focus on insulin sensitivity and ectopic fat deposition. Moreover, we addressed the question whether these effects may differ between individuals according to gender and the genetic background. The first study was designed to evaluate the impact of a 4-week HFrD on insulin sensitivity and lipid metabolism in 7 healthy men. Insulin sensitivity, intrahepatocellular lipids (IHCL) and intramyocellular lipids (IMCL) contents were measured before and after 1 and 4 weeks of HFrD (1.5 g fructose/kg body weight/day). Insulin sensitivity was assessed by a 2-step hyperinsulinemic euglycemic clamp. IHCL and IMCL were measured by 1H-magnetic resonance spectroscopy (MRS). Fructose caused significant (P<0.05) increases in fasting plasma concentrations of triacylglycerol (TG) (+36%), VLDL-TG (+72%) and glucose (+6%) without any change in body weight, IHCL, IMCL, and insulin sensitivity. In the second study, muscle biopsies were taken from five of these healthy male subjects before and after 4 weeks of HFrD. mRNA concentrations of 18 genes involved in lipid and carbohydrate metabolism were quantified by real-time quantitative PCR. We found that a 4-week HFrD increased the expression of genes involved in lipid synthesis, while it decreased those involved in insulin sensitivity and lipid oxidation; these molecular changes maybe early markers of insulin resistance and altered lipid metabolism. The third study aimed at delineating whether male and females equally respond to a HFrD. For this purpose, higher doses of fructose (twice the dose of the previous study) were provided to 8 healthy young males and 8 healthy young females over 6 days. HFrD significantly increased fasting TG in males (+71 %), whereas this increase was markedly blunted in females (+16%). Males also developed hepatic insulin resistance, characterized by increased hepatic glucose output (+12%), and showed higher alanine aminotransferase concentration (+38%), but none of these effect was observed in females. This study suggests that short-term HFrD leads to hypertriglyceridemia and hepatic insulin resistance in men, but premenopausal women seem protected against these effects. Finally, the fourth study investigated whether healthy offspring of type 2 diabetic patients (OffT2D), a subgroup of individuals prone to metabolic disorders due to their genetic background, may have exacerbated response to HFrD. Eight healthy males (Ctrl) and 16 OffT2D received a HFrD and isocaloric diet in a randomized order. In both groups, HFrD significantly increased IHCL (Ctrl: +76%; OffT2D: +79%) and fasting plasma VLDL-TG (Ctrl: +51 %; OffT2D: +110%). In absolute values, these increments were significantly higher in OffT2D, suggesting that these individuals may be more prone to developing metabolic disorders when challenged by high fructose intake. In order to better delineate the specific effects of fructose vs the hypercaloric energy content, we repeated the complete metabolic investigations after an isocaloric high glucose diet in four of the eight Ctrl volunteers. After a high glucose diet, TG and IHCL concentrations remained similar to the control values, in contrast to the marked increases observed after the HFrD. In conclusion, the studies included in this thesis provided novel insights into the metabolic effects of fructose in humans. They showed that fructose may rapidly increase fasting VLDL-TG, IHCL and lead to hepatic insulin resistance; these effects seem specific to fructose, and potential mechanisms may involve both stimulation of hepatic de novo lipogenesis and decreased lipid oxidation. Moreover, the results suggest that women seem protected against such deleterious effects, while OffT2D displayed exacerbated response. Résumé : Le fructose est un sucre simple, dont la consommation a augmenté durant les dernières décennies. Dans les modèles animaux, un régime riche en fructose (RRFru) peut induire plusieurs composantes du syndrome métabolique. Le but de cette thèse était d'étudier les effets d'un régime riche en fructose sur la sensibilité à l'insuline et la déposition de lipides ectopiques chez l'humain, et si ces effets variaient selon le genre ou le background génétique. La première étude avait pour but d'évaluer l'effet d'un RRFru d'une durée de 4 semaines sur la sensibilité à l'insuline et le métabolisme des lipides chez des hommes sains. La sensibilité à l'insuline, les lipides intrahépatiques (IHCL) et intramusculaires (IMCL) ont été mesurés avant, et après 1 et 4 semaines du RRFru (1.5 g fructose/kg/jour). La sensibilité à l'insuline a été déterminée par un clamp hyperinsulinémique euglycémique, et les IHCL/IMCL par spectroscopie à résonnance magnétique. Le fructose a augmenté les concentrations plasmatiques à jeun des VLDL- triglycérides (TG) (+72%) et de glucose (+6%), sans induire de changement au niveau de la sensibilité à l'insuline, IHCL ou IMCL. Dans la deuxième étude, des biopsies de muscle squelettique ont été prélevées chez cinq de ces volontaires avant et après les 4 semaines de RRFru. Les concentrations de mRNA de 18 gènes impliqués dans le métabolisme des lipides et des hydrates de carbone ont été mesurées par RT-PCR quantitative. Le RRFru a augmenté l'expression de gènes impliqués dans la synthèse de lipides, et diminué celles de gènes impliqués dans la sensibilité à l'insuline et l'oxydation de lipides. Ces changements pourraient constituer des altérations précoces de la sensibilité à l'insuline et du métabolisme lipidique en réponse au fructose. La troisième étude avait pour but de définir si les réponses au RRFru étaient semblables entre les hommes et les femmes. Pour ceci, des doses plus élevées de fructose ont été administrées à 8 jeunes hommes et 8 jeunes femmes durant 6 jours. Le RRFru a augmenté les TG chez les hommes (+71 %), et de manière nettement plus modeste chez les femmes (+16%). Les hommes ont développé une résistance hépatique à l'insuline, ainsi qu'une augmentation des concentrations d'alanine aminotransférase (+38%), mais aucun de ces effets n'a été observé chez les femmes. Cette étude suggère qu'à court terme, un RRFru mène à une hypertriglycéridémie et résistance hépatique à l'insuline chez l'homme, tandis que les femmes semblent en être protégées. Finalement, la 4ème étude a investigué si des personnes apparentées à des patients diabétiques de type 2 (AppDT2), qui constituent un groupe d'individus à risque de développer des maladies métaboliques en raison de leur background génétique, avaient des réponses plus marquées au RRFru. Huit hommes sains (Ctrl) et 16 AppDT2 on reçu dans un ordre randomisé un RRFru et une diète isocalorique durant 6 jours. Dans les deux groupes, le RRFru a augmenté significativement les IHCL (Ctrl: +76%; AppDT2: +79%) et les VLDL-TG plasmatiques à jeun (Ctrl: +51%; AppDT2: +110%). En valeurs absolues, ces deux augmentations étaient plus importantes dans le groupe des AppDT2, suggérant que ces individus sont plus à risque de développer des problèmes métaboliques suite à un apport de fructose. Afin de définir les effets spécifiques du fructose, quatre des huit sujets Ctrl ont été soumis à un régime riche en glucose. Après le régime riche en glucose, les concentrations de TG et d'IHCL étaient semblables aux valeurs obtenues après une diète isocalorique, contrairement aux nombreux effets observés après le RRFru. En conclusion, ces différentes études ont démontré que chez l'humain, le fructose peut rapidement induire une augmentation des VLDL-TG à jeun, des IHCL et une résistance hépatique à l'insuline ; ces effets semblent être spécifiques au fructose. De plus, les différents résultats obtenus montrent que les femmes développent des effets moindres en réponse au fructose, contrairement aux AppDT2, chez qui les effets du fructose semblent plus marqués. Résumé grand public : Le fructose est un sucre simple, présent naturellement et en faibles quantités dans les fruits, mais également constituant du sucrose - appelé aussi sucre de table. Depuis les années 1970, la consommation de fructose a augmenté dans les pays industrialisés et émergents, principalement par le biais d'une hausse de consommation de boissons sucrées de type soda. Dans des modèles animaux tels que les rongeurs, un régime riche en fructose mène au développement de plusieurs facteurs de risques étroitement liés aux maladies cardiovasculaires, à l'obésité et au diabète de type 2; ceux-ci sont caractérisés par une augmentation des concentrations de glucose et de lipides sanguins, ainsi qu'une accumulation de lipides dits « ectopiques », à savoir dans le foie et les muscles. Le but de cette thèse était de définir les effets d'un régime riche en fructose chez l'être humain. De plus, nous nous sommes intéressés à savoir si ces effets étaient semblables entre différents groupes d'individus, à savoir des personnes de sexe masculin / féminin, ou des personnes dont au moins un des parents est diabétique de type 2. Pour ceci, différents groupes de volontaires (hommes, femmes, avec histoire familiale de diabète de type 2) âgés de 18-30 ans se sont soumis à une alimentation enrichie en fructose, d'une durée allant de 6 à 28 jours, suivant l'étude à laquelle ils participaient. La quantité de fructose consommée en plus de l'alimentation normale durant ces périodes équivalait au contenu en fructose de 2-4 litres de boissons sucrées par jour. Des prises de sang ont été effectuées au terme de chacun de ces différents régimes, ainsi que des mesures de sensibilité à l'insuline et de concentrations de lipides dans le foie et le muscle par résonnance magnétique nucléaire, en collaboration avec l'Hôpital de l'Ile de Berne. Les résultats montrent qu'après 6 jours de régime riche en fructose, les volontaires sains de sexe masculin ont presque doublé leurs concentrations de lipides sanguins et hépatiques. De plus, le foie de ces volontaires réagissait moins bien à l'insuline, ce qui pourrait mener à long terme à des maladies métaboliques comme le diabète de type 2. Un des mécanismes postulés est que le fructose pourrait stimuler la formation de lipides dans le foie, contribuant ainsi à un dysfonctionnement de cet organe. De manière surprenante, des femmes d'âge et d'IMC (Indice de Masse Corporelle) comparables aux hommes étudiés n'ont pas développé ces différents effets en réponse au régime riche en fructose. Il semblerait donc qu'elles possèdent certaines propriétés pouvant les «protéger », du moins à court terme, des problèmes métaboliques induits par le fructose. De tels mécanismes sont pour l'heure inconnus, mais il est possible que des différences hormonales, ou de répartition de la masse graisseuse dans le corps, puissent jouer un rôle. Enfin, nous avons également démontré que chez certaines personnes ayant au moins un parent (père ou mère) diabétique de type 2, les augmentations de lipides sanguins et hépatiques induits par le fructose étaient plus marquées que chez des volontaires sans parents diabétiques. Ceci est néanmoins à tempérer par le fait que nous avons observé une grande hétérogénéité des réponses parmi ces individus, découlant certainement d'interactions complexes entre différents facteurs tels que la génétique, le mode de vie, l'alimentation et l'activité physique. Ces différents résultats donnent lieu à une meilleure compréhension du rôle de facteurs alimentaires dans le développement de problèmes métaboliques tels que le diabète de type 2. Ils vont également permettre de tester différentes approches thérapeutiques. Bien qu'ayant été obtenus avec des doses de fructose importantes, ces études soulignent l'effet potentiellement dangereux pour la santé d'une alimentation riche en sucres.

Nutrición, fibrosis quística y aparato digestivo

The prevalence of hyponutrition in cystic fibrosis is high although it may vary according to the different studies. Detection of hyponutrition should be done by combining different methods, depending on their availability. However, the simplest and most validated criterion is to measure at each visit the weight (and height in children) in order to calculate the body mass index and categorizing hyponutrition according to absolute criteria: in adults < 18.5 kg/m(2), and in children as percentiles of the body mass index. Worsening of the nutritional status is directly related with the decrease in lung function parameters and it has been proposed as a morbidity (and even mortality) predictive factor in people with cystic fibrosis, independently of the level of pulmonary dysfunction. Exocrine pancreatic insufficiency is present is approximately 70-90% of the patients with cystic fibrosis and the genotype-phenotype correlation is high. Most of the patients with exocrine pancreatic insufficiency tolerate a high-fat diet provided that they are treated with pancreatic enzymes at appropriate doses. The prevalence of diabetes increases with age, reaching up 40% of the cases in patients older than 30 years. Clinical liver involvement is less prevalent (it approximately affects 1/3 of the patients). Other intestinal complications such as meconial ileus, gastroesophageal reflux, obstruction of the distal intestine, or fibrosing colon disease may also condition malnourishment. In patients with cystic fibrosis, a usual high-fat diet providing 120%-150% of the recommended calories is advised. If the nutritional goals are not achieved or maintained with diet modifications, artificial supplements may be added, although the recommendation for their use has not been endorsed by solid scientific evidences. The most frequently used preparations usually are polymeric or hypercaloric. The indications for enteral (through a tube, especially gastrostomy) or parenteral nutritional support are similar to those used in other pathologies. Dietary and nutritional control should be included in a multidisciplinary program allowing the improvement of the functional capacity and the quality of life and reducing, at least from a theoretical viewpoint, the morbimortality associated to malnourishment in these patients.

Connexin40 regulates renin production and blood pressure.

Renin secretion is regulated by coordinated signaling between the various cells of the juxtaglomerular apparatus. The renin-secreting cells (RSC), which play a major role in the control of blood pressure, are coupled to each other and to endothelial cells by Connexin40 (Cx40)-containing channels. In this study, we show that Cx40 knockout (Cx40-/-) mice, but not their heterozygous littermates, are hypertensive due to the increase in the number of RSC, renin biosynthesis, and plasma renin. Treatment with the angiotensin II receptor AT1 antagonist candesartan or the angiotensin II-converting enzyme inhibitor ramipril reduced the blood pressure of the Cx40-/- mice to the same levels seen in wild-type (WT) mice. The elevated blood pressure of the knockout mice was not affected by clipping one renal artery (2K1C, renin-dependent model of hypertension) or after a high salt diet. Under these conditions, however, Cx40-/- mice showed an altered production and release of renin. The renin mRNA ratio between the clipped and the non-clipped kidney was lower in the knockout than in the WT 2K1C mice. This indicates that the response to a change in blood pressure was altered. The RSC of the Cx40-/- mice did not have a compensatory increase in the levels of either Cx43 or Cx37. Our data show that renin secretion is dependent on Cx40 and suggest the Cx40-/- mice may be a genetic model of renin-dependent hypertension.

The glucocorticoid-induced leucine zipper (gilz/tsc22d3-2) gene locus plays a crucial role in male fertility.

The glucocorticoid-induced leucine zipper (Tsc22d3-2) is a widely expressed dexamethasone-induced transcript that has been proposed to be important in immunity, adipogenesis, and renal sodium handling based on in vitro studies. To address its function in vivo, we have used Cre/loxP technology to generate mice deficient for Tsc22d3-2. Male knockout mice were viable but surprisingly did not show any major deficiencies in immunological processes or inflammatory responses. Tsc22d3-2 knockout mice adapted to a sodium-deprived diet and to water deprivation conditions but developed a subtle deficiency in renal sodium and water handling. Moreover, the affected animals developed a mild metabolic phenotype evident by a reduction in weight from 6 months of age, mild hyperinsulinemia, and resistance to a high-fat diet. Tsc22d3-2-deficient males were infertile and exhibited severe testis dysplasia from postnatal d 10 onward with increases in apoptotic cells within seminiferous tubules, an increased number of Leydig cells, and significantly elevated FSH and testosterone levels. Thus, our analysis of the Tsc22d3-2-deficient mice demonstrated a previously uncharacterized function of glucocorticoid-induced leucine zipper protein in testis development.

Interaction between dietary lipids an physical inactivity on insulin sensitivity and on intramyocellular lipids in healthy men

Résumé Interaction entre les lipides alimentaires et l'inactivité physique sur la sensibilité à l'insuline et les lipides intramyocellulaires chez le sujet masculin en bonne santé Ces deux dernières décennies, l'incidence de la résistance à l'insuline n'a cessé de progresser dans les pays industrialisés. Un grand nombre de travaux suggèrent que ce trouble métabolique joue un rôle important dans la pathogenèse de maladies propres au monde industrialisé, telles que le diabète, l'hypertension et les maladies cardiovasculaires. Malgré de nombreuses études, les mécanismes à l'origine de la résistance à l'insuline restent encore incomplètement élucidés. En plus d'une composante génétique, de nombreux facteurs environnementaux semblent impliqués parmi ces derniers, nous nous sommes intéressés à l'effet d'une alimentation riche en graisses associée à une période d'inactivité physique de courte durée. Nous nous sommes également penchés sur la corrélation décrite entre la résistance à l'insuline et la concentration de graisses présentes à l'intérieur des cellules musculaires squelettiques, appelées lipides intramyocellulaires. Pour ce faire, 8 volontaires masculins ont été étudiés à deux occasions. Après deux jours de diète équilibrée associée à une activité physique, les participants étaient confinés au lit strict pour 60 heures et devaient manger une alimentation soit riche en graisses saturées soit riche en hydrates de carbones. Pour évaluer l'effet de l'alimentation seule, 6 des 8 volontaires ont été réétudiés après deux jours de diète équilibrée suivie par 60 heures d'alimentation riche en graisses saturées associées à une activité physique contrôlée. Nous avons estimé la sensibilité à l'insuline par la technique du clamp hyperinsulinémique euglycémique alors que la concentration de lipides intramyocellulaires a été déterminée par spectroscopie par résonance magnétique. Après 60 heures d'inactivité physique associée à une alimentation riche en lipides, nous avons observé une diminution de l'utilisation de glucose dépendante de l'insuline (-24±6%; p<0.05), alors qu'aucune modification significative de ce même paramètre n'a été constatée lorsque l'inactivité physique était associée à une alimentation riche en hydrates de carbones (+19±10%). Ces deux conditions se sont accompagnées d'une augmentation des lipides intramyocellulaires (+32±7% et +17±8% respectivement). Bien que l'augmentation des lipides intramyocellulaires observée après 60 heures d'une alimentation riche en graisses saturées associée à une activité physique modérée fût d'une ampleur similaire à celle de la condition associant une alimentation riche en graisses et inactivité physique, l'utilisation de glucose induite par l'insuline n'a pas été modifiée de manière significative (-7±9%) Ces résultats indiquent que l'inactivité physique et une alimentation riche en graisses saturées semblent interagir, induisant une diminution de la sensibilité à l'insuline globale. La concentration de lipides intramyocellulaires a été influencée par les lipides issus de l'alimentation et l'inactivité physique, sans être toutefois corrélée à la résistance à l'insuline. Abstract OBJECTIVE - To assess the effect of a possible interaction between dietary fat and physical inactivity on whole-body insulin sensitivity and intramyocellular lipids (IMCLs). RESEARCH DESIGN AND METHODS - Eight healthy male volunteers were studied on two occasions. After 2 days of an equilibrated diet and moderate physical activity, participants remained inactive (bed rest) for 60 h and consumed either a high-saturated fat (45% fat, of which ~60% was saturated fat [BR-HF]) or a high-carbohydrate (70% carbohydrate [BR-HCHO]) diet. To evaluate the effect of a high-fat diet alone, six of the eight volunteers were restudied after a 2-day equilibrated diet followed by 60 h on a high-saturated fat diet and controlled physical activity (PA-HF). Insulin sensitivity was measured by hyperinsulinemic-euglycemic clamp and IMCL concentrations by H-magnetic resonance spectroscopy. RESULTS - Insulin-mediated glucose disposal was decreased by BR-HF condition (-24 ± 6%, P < 0.05) but did not change with BR-HCHO ( + 19 ± 10%, NS). BR-HF and BR-HCHO increased IMCL levels (+32 ± 7%, P < 0.05 and +17 ± 8%, P < 0.0011, respectively). Although the increase in IMCL levels with PA-HF (+31 ± 19%, P = 0.12) was similar to that during BR-HF, insulin-mediated glucose disposal ( -7 ± 9%, NS) was not decreased. CONCLUSIONS - These data indicate that physical inactivity and a high-saturated fat diet may interact to reduce whole-body insulin sensitivity. IMCL content was influenced by dietary lipid and physical inactivity but was not directly associated with insulin resistance.

Leucine supplementation protects from insulin resistance by regulating adiposity levels.

BACKGROUND Leucine supplementation might have therapeutic potential in preventing diet-induced obesity and improving insulin sensitivity. However, the underlying mechanisms are at present unclear. Additionally, it is unclear whether leucine supplementation might be equally efficacious once obesity has developed. METHODOLOGY/PRINCIPAL FINDINGS Male C57BL/6J mice were fed chow or a high-fat diet (HFD), supplemented or not with leucine for 17 weeks. Another group of HFD-fed mice (HFD-pairfat group) was food restricted in order to reach an adiposity level comparable to that of HFD-Leu mice. Finally, a third group of mice was exposed to HFD for 12 weeks before being chronically supplemented with leucine. Leucine supplementation in HFD-fed mice decreased body weight and fat mass by increasing energy expenditure, fatty acid oxidation and locomotor activity in vivo. The decreased adiposity in HFD-Leu mice was associated with increased expression of uncoupling protein 3 (UCP-3) in the brown adipose tissue, better insulin sensitivity, increased intestinal gluconeogenesis and preservation of islets of Langerhans histomorphology and function. HFD-pairfat mice had a comparable improvement in insulin sensitivity, without changes in islets physiology or intestinal gluconeogenesis. Remarkably, both HFD-Leu and HFD-pairfat mice had decreased hepatic lipid content, which likely helped improve insulin sensitivity. In contrast, when leucine was supplemented to already obese animals, no changes in body weight, body composition or glucose metabolism were observed. CONCLUSIONS/SIGNIFICANCE These findings suggest that leucine improves insulin sensitivity in HFD-fed mice by primarily decreasing adiposity, rather than directly acting on peripheral target organs. However, beneficial effects of leucine on intestinal gluconeogenesis and islets of Langerhans's physiology might help prevent type 2 diabetes development. Differently, metabolic benefit of leucine supplementation is lacking in already obese animals, a phenomenon possibly related to the extent of the obesity before starting the supplementation.

In vivo assessment of antiretroviral therapy-associated side effects

Antiretroviral therapy has been associated with side effects, either from the drug itself or in conjunction with the effects of human immunodeficiency virus infection. Here, we evaluated the side effects of the protease inhibitor (PI) indinavir in hamsters consuming a normal or high-fat diet. Indinavir treatment increased the hamster death rate and resulted in an increase in triglyceride, cholesterol and glucose serum levels and a reduction in anti-oxLDL auto-antibodies. The treatment led to histopathological alterations of the kidney and the heart. These results suggest that hamsters are an interesting model for the study of the side effects of antiretroviral drugs, such as PIs.

Experimental bacterial endocarditis after dental extractions in rats with periodontitis.

The development of bacterial endocarditis was analyzed after dental extractions in rats with or without periodontal disease. Periodontal disease was produced in rats by tying silk ligatures around the two maxillary first molars and placing the animals on a high sucrose diet for 14 weeks. Sterile aortic valve vegetations were produced by means of a transaortic catheter, and 24 hr later the maxillary first molars were extracted. The animals were killed 72 hr after the extractions. In rats with periodontal disease, extractions resulted in a 48% (14 of 29) incidence of bacterial endocarditis, most cases of which were due to Streptococcus spp. (one was caused by Staphylococcus aureus). In contrast, when the teeth with a healthy periodontium were extracted, only 6% (one of 15) of the rats developed endocarditis. When catheters were placed in animals with periodontal disease but no extractions were performed, no endocarditis occurred.

Deletion of Sirt3 does not affect atherosclerosis but accelerates weight gain and impairs rapid metabolic adaptation in LDL receptor knockout mice: implications for cardiovascular risk factor development.

Sirt3 is a mitochondrial NAD(+)-dependent deacetylase that governs mitochondrial metabolism and reactive oxygen species homeostasis. Sirt3 deficiency has been reported to accelerate the development of the metabolic syndrome. However, the role of Sirt3 in atherosclerosis remains enigmatic. We aimed to investigate whether Sirt3 deficiency affects atherosclerosis, plaque vulnerability, and metabolic homeostasis. Low-density lipoprotein receptor knockout (LDLR(-/-)) and LDLR/Sirt3 double-knockout (Sirt3(-/-)LDLR(-/-)) mice were fed a high-cholesterol diet (1.25 % w/w) for 12 weeks. Atherosclerosis was assessed en face in thoraco-abdominal aortae and in cross sections of aortic roots. Sirt3 deletion led to hepatic mitochondrial protein hyperacetylation. Unexpectedly, though plasma malondialdehyde levels were elevated in Sirt3-deficient mice, Sirt3 deletion affected neither plaque burden nor features of plaque vulnerability (i.e., fibrous cap thickness and necrotic core diameter). Likewise, plaque macrophage and T cell infiltration as well as endothelial activation remained unaltered. Electron microscopy of aortic walls revealed no difference in mitochondrial microarchitecture between both groups. Interestingly, loss of Sirt3 was associated with accelerated weight gain and an impaired capacity to cope with rapid changes in nutrient supply as assessed by indirect calorimetry. Serum lipid levels and glucose tolerance were unaffected by Sirt3 deletion in LDLR(-/-) mice. Sirt3 deficiency does not affect atherosclerosis in LDLR(-/-) mice. However, Sirt3 controls systemic levels of oxidative stress, limits expedited weight gain, and allows rapid metabolic adaptation. Thus, Sirt3 may contribute to postponing cardiovascular risk factor development.

Cell autonomous lipin 1 function is essential for development and maintenance of white and brown adipose tissue.

Through analysis of mice with spatially and temporally restricted inactivation of Lpin1, we characterized its cell autonomous function in both white (WAT) and brown (BAT) adipocyte development and maintenance. We observed that the lipin 1 inactivation in adipocytes of aP2(Cre/+)/Lp(fEx2)(-)(3/fEx2)(-)(3) mice resulted in lipodystrophy and the presence of adipocytes with multilocular lipid droplets. We further showed that time-specific loss of lipin 1 in mature adipocytes in aP2(Cre-ERT2/+)/Lp(fEx2)(-)(3/fEx2)(-)(3) mice led to their replacement by newly formed Lpin1-positive adipocytes, thus establishing a role for lipin 1 in mature adipocyte maintenance. Importantly, we observed that the presence of newly formed Lpin1-positive adipocytes in aP2(Cre-ERT2/+)/Lp(fEx2)(-)(3/fEx2)(-)(3) mice protected these animals against WAT inflammation and hepatic steatosis induced by a high-fat diet. Loss of lipin 1 also affected BAT development and function, as revealed by histological changes, defects in the expression of peroxisome proliferator-activated receptor alpha (PPARα), PGC-1α, and UCP1, and functionally by altered cold sensitivity. Finally, our data indicate that phosphatidic acid, which accumulates in WAT of animals lacking lipin 1 function, specifically inhibits differentiation of preadipocytes. Together, these observations firmly demonstrate a cell autonomous role of lipin 1 in WAT and BAT biology and indicate its potential as a therapeutical target for the treatment of obesity.

Omega-3 fatty acids prevent inflammation and metabolic disorder through inhibition of NLRP3 inflammasome activation.

Omega-3 fatty acids (ω-3 FAs) have potential anti-inflammatory activity in a variety of inflammatory human diseases, but the mechanisms remain poorly understood. Here we show that stimulation of macrophages with ω-3 FAs, including eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and other family members, abolished NLRP3 inflammasome activation and inhibited subsequent caspase-1 activation and IL-1β secretion. In addition, G protein-coupled receptor 120 (GPR120) and GPR40 and their downstream scaffold protein β-arrestin-2 were shown to be involved in inflammasome inhibition induced by ω-3 FAs. Importantly, ω-3 FAs also prevented NLRP3 inflammasome-dependent inflammation and metabolic disorder in a high-fat-diet-induced type 2 diabetes model. Our results reveal a mechanism through which ω-3 FAs repress inflammation and prevent inflammation-driven diseases and suggest the potential clinical use of ω-3 FAs in gout, autoinflammatory syndromes, or other NLRP3 inflammasome-driven inflammatory diseases.

The anorexigenic effects of metformin involve increases in hypothalamic leptin receptor expression.

Metformin demonstrates anorectic effects in vivo and inhibits neuropeptide Y expression in cultured hypothalamic neurons. Here we investigated the mechanisms implicated in the modulation of feeding by metformin in animals rendered obese by long-term high-fat diet (diet-induced obesity [DIO]) and in animals resistant to obesity (diet resistant [DR]). Male Long-Evans rats were kept on normal chow feeding (controls) or on high-fat diet (DIO, DR) for 6 months. Afterward, rats were treated 14 days with metformin (75 mg/kg) or isotonic sodium chloride solution and killed. Energy efficiency, metabolic parameters, and gene expression were analyzed at the end of the high-fat diet period and after 14 days of metformin treatment. At the end of the high-fat diet period, despite higher leptin levels, DIO rats had higher levels of hypothalamic neuropeptide Y expression than DR or control rats, suggesting a central leptin resistance. In DIO but also in DR rats, metformin treatment induced significant reductions of food intake accompanied by decreases in body weight. Interestingly, the weight loss achieved by metformin was correlated with pretreatment plasma leptin levels. This effect was paralleled by a stimulation of the expression of the leptin receptor gene (ObRb) in the arcuate nucleus. These data identify the hypothalamic ObRb as a gene modulated after metformin treatment and suggest that the anorectic effects of the drug are potentially mediated via an increase in the central sensitivity to leptin. Thus, they provide a rationale for novel therapeutic approaches associating leptin and metformin in the treatment of obesity.

Intestinal gluconeogenesis is a key factor for early metabolic changes after gastric bypass but not after gastric lap-band in mice.

Unlike the adjustable gastric banding procedure (AGB), Roux-en-Y gastric bypass surgery (RYGBP) in humans has an intriguing effect: a rapid and substantial control of type 2 diabetes mellitus (T2DM). We performed gastric lap-band (GLB) and entero-gastro anastomosis (EGA) procedures in C57Bl6 mice that were fed a high-fat diet. The EGA procedure specifically reduced food intake and increased insulin sensitivity as measured by endogenous glucose production. Intestinal gluconeogenesis increased after the EGA procedure, but not after gastric banding. All EGA effects were abolished in GLUT-2 knockout mice and in mice with portal vein denervation. We thus provide mechanistic evidence that the beneficial effects of the EGA procedure on food intake and glucose homeostasis involve intestinal gluconeogenesis and its detection via a GLUT-2 and hepatoportal sensor pathway.