Effets de la modulation de la masse grasse sur la production d'adiponectine chez la souris (conséquences sur le métabolisme hépatique des lipides)

L adiponectine (ApN) est une adipokine de 30 KDa produite abondamment par le tissu adipeux qui a été décrite pour la première fois en 1995. Dès lors qu une corrélation inverse entre les taux circulants d ApN et l adiposité a été mise en évidence, de très nombreuses études ont été initiées pour chercher à établir un lien avec les pathologies liées au syndrome métabolique. Ainsi, chez les patients obèses et diabétiques, une perte de poids induite par un traitement médicamenteux ou un régime hypocalorique s accompagne d une augmentation des taux circulants d ApN et d une amélioration des paramètres biochimiques. Il ressort de ces études que des taux élevés d ApN sont corrélés à une amélioration de la sensibilité à l insuline, des paramètres lipidiques et une diminution du risque cardiovasculaire. Cependant, les mécanismes d action conduisant à l amélioration du métabolisme lipidique et glucidique restent encore mal connus. Au cours de cette étude, nous avons, dans un premier temps, cherché à déterminer les conséquences d une variation de la masse grasse sur la production de l ApN chez la souris. Pour cela, différentes stratégies nutritionnelles et pharmacologiques, conduisant à une fonte ou à une augmentation de la masse grasse, ont utilisées. Les résultats obtenus suggèrent que la production d ApN n est pas dépendante de la taille des adipocytes mais plutôt de leur état inflammatoire. Dans un second temps, grâce à un modèle d explants de foie en culture, nous avons cherché à déterminer les effets directs de l ApN sur le métabolisme lipidique du foie. Une première approche a consisté à tester les effets à long terme c est à dire susceptibles de correspondre à des modifications d expression génique et de synthèse protéique en incubant les explants pendant 21h dans un milieu de culture contenant de l ApN en présence ou non d insuline. Les résultats suggèrent que l ApN accentue les effets de l insuline, ce qui se traduit par une meilleure utilisation du glucose avec en contre partie une stimulation de la lipogenèse et une réduction de la ß-oxydation en présence d insuline. De plus, l ApN apparaît exercer un effet sur les voies de catabolisme des HDL. Par une seconde approche, nous avons testé les effets à court terme de l ApN sur les capacités b-oxydatives en traitant les explants pendant 45 min. Dans ces conditions plus appropriées pour mettre en évidence l activation des voies de régulation rapides, la présence d ApN entraine une stimulation de la ß-oxydation qui s accompagne d une augmentation de la p- AMPK. En conclusion, ces résultats suggèrent que l ApN exerce des effets directs sur le métabolisme hépatique du glucose compatible avec l effet insulino-sensibilisateur observé in vivo. En revanche, les résultats ne permettent pas, à ce stade, d établir une relation entre une induction par l ApN de l activité ß-oxydative des acides gras dans le foie et ces effets bénéfiques sur les paramètres lipidiques.Adiponectin (ApN), a 30-kDa adipokine abundantly produced by adipose tissue has been described for the first time in 1995. Early findings demonstrating serum adiponectin levels are inversely correlated with obesity initiated intense investigation of the relationship between adiponectin and all symptoms of the metabolic syndrome. Of these studies, strong evidence suggests that a weight loss induced by medication or hypocaloric diet led to increased circulating ApN levels and improvement of biochemical parameters. Thus, high levels of ApN have been correlated with an improvement of insulin sensitivity and lipid parameters reducing cardiovascular risk. However mechanisms involved in the improvement of glucose and lipid metabolism are not fully understood. In this study, we wanted to determine whether variations of plasma ApN levels are associated with alterations of liver lipid metabolism in mice. For this, we used different nutritional and pharmacological strategies to induce fat mass variations and measured corresponding ApN production and lipid parameters. First, results suggested that production of ApN is not dependent on the size of adipocytes, but rather to their inflammatory state. The effect of ApN of liver metabolism was further studied using an in vitro model of liver explants in culture. A first approach consists of testing the long-term effects of ApN on liver incubating the slices for 21h in the presence or not of insulin. Biochemical and molecular data suggested that ApN accentuates the effects of insulin, resulting in improvement of glucose utilization associated with a stimulation of lipogenesis and a reduction in b-oxidation in the presence of insulin. In addition, ApN appears to affect HDL catabolism pathways. In a second approach, we tested the short-term effects of ApN on b-oxidative capacity treating the slices for 45 min. Under these conditions more appropriated to highlight the activation of fast regulatory pathways, ApN induced a stimulation of ß-oxidation which was accompanied by an increase in p-AMPK. In conclusion, data suggested that ApN has direct effects on hepatic glucose metabolism consistent with the insulin-sensitizer effect demonstrated in vivo. However, at this stage, these results did not give evidence of a relationship between induction of liver fatty acid b- oxidation by ApN and its beneficial effects on lipid parameters.DIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Impact du système endocannabinoïdien sur la physiologie de l'obésité (effets de l'antagonisme des récepteurs CB1 sur le métabolisme glucido-lipidique de la souris obèse)

Le système endocannabinoïdien (SEC) est impliqué dans de nombreuses fonctions biologiques comme la régulation du métabolisme énergétique. Ces dernières années, de nombreuses études ont montré que l obésité était associée à une suractivation du SEC et en particuliers des récepteurs CB1 (CB1R) centraux. De plus, l inactivation des CB1R par des antagonistes spécifiques comme le Rimonabant (SR141716) conduits à une amélioration des paramètres métaboliques chez le sujet obèse. Cependant, l inactivation des CB1R périphériques pourrait également contribuer à l amélioration de ces paramètres et c est cette dernière notion que nous avons cherché à approfondir. Pour cela, nous avons testé les effets du SR141716, sur des souris obèses afin d établir des relations entre l activité du SEC et le statut lipidique en étudiant plus particulièrement la régulation du métabolisme dans deux tissus clé, le foie et le tissu adipeux (TA). Des souris préalablement rendues obèses via un régime alimentaire enrichi en sucre et en graisse ont été traitées 6 semaines par SR141716 et le traitement à conduit à une perte de poids associée à une normalisation paramètres plasmatiques ainsi qu à une résorption de la stéatose hépatique. L hypothèse majeure de cette étude est que la réversion de la stéatose serait associée à un effet bénéfique du traitement sur le métabolisme du TA viscéral et qu il y aurait donc des effets directs du SR141716 sur les tissus périphériques. Par conséquent, les effets de l antagonisme des CB1R périphériques sur le métabolisme lipidique ont ensuite été étudiés in vitro. Pour cela, nous avons tout d abord développé un modèle d explants de foie en culture traités avec SR141716. Dans ce modèle, le blocage des CB1R hépatiques est associé à une diminution de leur expression génique et dans certaines conditions à une augmentation des capacités -oxydatives. Enfin, afin d étudier l impact du SEC sur le métabolisme adipocytaire, nous avons mis au point un modèle d explants de TA en culture en distinguant le TA viscéral du sous-cutané. Des résultats préliminaires semblent indiquer que le blocage des CB1R limite la lipolyse dans le TA viscéral. En conclusion, ces travaux de thèse démontrent que les CB1R périphériques constituent une cible thérapeutique très prometteuse pour le traitement de l obésité et des désordres associés.The endocannabinoïd system (ECS) is involved in many biological functions such as regulation of energy metabolism. Recently, several studies have shown an association between obesity and ECS overactivity. In addition, specific CB1R antagonists such as Rimonabant (SR141716) improved metabolic parameters in obese patients essentially through inactivation of central CB1R. However, peripheral CB1R inactivation could also contribute to the improvement of these parameters and it is this notion that we have studied. To this purpose, we tested the effects of SR141716 on obese mice in order to establish relationships between the ECS activity and lipid metabolism by looking more specifically to its regulation in two key tissues, the liver and the adipose tissue (AT). Obese mice previously fed with a high sucrose high fat diet were treated six weeks by SR141716 and this treatment induced weight loss associated with a normalization of plasmatic parameters and a reduction of hepatic steatosis. The major hypothesis of this study is that steatosis reversion was associated with a beneficial effect of treatment on visceral AT metabolism and that SR141716 would have direct effects on peripheral tissues. Therefore, these effects of CB1R antagonism on peripheral lipid metabolism have been studied in vitro. In this way, we first developed a model of liver explants in culture treated with SR141716. In this model, CB1R antagonism in the liver was associated with a decrease in CB1 gene expression and in certain conditions with an increased in -oxidative capacity. Finally, in order to study the impact of the ECS on adipocyte metabolism, we developed a model of cultured AT explants distinguishing visceral and subcutaneous AT. Preliminary results suggested that CB1R antagonism limits lipolysis in visceral AT. In conclusion, this work showed that peripheral CB1R are a very promising therapeutic target for treating obesity and related disorders.DIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Orosensory Detection of Dietary Fatty Acids Is Altered in CB1R−/− Mice

International audienceObesity is one of the major public health issues, and its prevalence is steadily increasing all the world over. The endocannabinoid system (ECS) has been shown to be involved in the intake of palatable food via activation of cannabinoid 1 receptor (CB₁R). However, the involvement of lingual CB₁R in the orosensory perception of dietary fatty acids has never been investigated. In the present study, behavioral tests on CB₁R-/- and wild type (WT) mice showed that the invalidation of Cb₁r gene was associated with low preference for solutions containing rapeseed oil or a long-chain fatty acid (LCFA), such as linoleic acid (LA). Administration of rimonabant, a CB₁R inverse agonist, in mice also brought about a low preference for dietary fat. No difference in CD36 and GPR120 protein expressions were observed in taste bud cells (TBC) from WT and CB₁R-/- mice. However, LCFA induced a higher increase in [Ca2+]i in TBC from WT mice than that in TBC from CB₁R-/- mice. TBC from CB₁R-/- mice also exhibited decreased Proglucagon and Glp-1r mRNA and a low GLP-1 basal level. We report that CB₁R is involved in fat taste perception via calcium signaling and GLP-1 secretion

Immunolocalisation of Fatty Acid Transporter (FAT) and liver fatty acid binding protein (L-FABPc) in the small intestine

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Acute activation of cannabinoid receptors by anandamide reduces gastrointestinal motility and improves postprandial glycemia in mice.

International audienceThe endocannabinoid system (ECS) is associated with an alteration of glucose homeostasis dependent on cannabinoid receptor-1 (CB1R) activation. However, very little information is available concerning the consequences of ECS activation on intestinal glucose absorption. Mice were injected intraperitoneally with anandamide, an endocannabinoid binding both CB1R and CB2R. We measured plasma glucose and xylose appearance after oral loading, gastrointestinal motility, and glucose transepithelial transport using the everted sac method. Anandamide improved hyperglycemia after oral glucose charge whereas glucose clearance and insulin sensitivity were impaired, pointing out some gastrointestinal events. Plasma xylose appearance was delayed in association with a strong decrease in gastrointestinal transit, while anandamide did not alter transporter-mediated glucose absorption. Interestingly, transit was nearly normalized by coinjection of SR141716 and AM630 (CB1R and CB2R antagonist, respectively), and AM630 also reduced the delay of plasma glucose appearance induced by anandamide. When gastric emptying was bypassed by direct glucose administration in the duodenum, anandamide still reduced plasma glucose appearance in wild-type but not in CB1R(-/-) mice. In conclusion, our findings demonstrated that acute activation of intestinal ECS reduced postprandial glycemia independently on intestinal glucose transport but rather inhibiting gastric emptying and small intestine motility and strongly suggest the involvement of both CB1R and CB2R

Fatty acid regulation of fatty acid-binding protein expression in the small intestine

International audienceThe effects of dietary oil intake and fatty acid infusions on the expression of intestinal and liver fatty acid-binding proteins (I-FABP and L-FABP, respectively) were investigated in the small intestine of mice. A daily force-feeding for 7 days with 0.2 ml sunflower oil specifically increased L-FABP mRNA and protein levels in duodenum and proximal jejunum. This upregulation was mediated in time- and dose-dependent manners by a minute quantity of linoleic acid, the main fatty acid found in sunflower oil. The L-FABP induction was only found with long-chain fatty acids, with the nonmetabolizable, substituted fatty acid alpha-bromopalmitate being far more active. A hormonally mediated effect is unlikely because long-chain fatty acids induced L-FABP mRNA in the Caco-2 cell line cultured in serum-free medium. Therefore, long-chain fatty acids are strong inducers of L-FABP gene expression in the small intestine. In contrast to data found in the rat, I-FABP gene expression appears to be unaffected by a lipid-enriched diet in the mouse

Hepatic steatosis is not due to impaired fatty acid oxidation capacities in C57BL/6J fed the conjugated trans-10, cis-12-isomer of linoleic acid

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Therapeutic potential of a novel peripherally restricted CB1R inverse agonist on the progression of diabetic nephropathy

International audienceObjective: This study assessed the efficacy of INV-202, a novel peripherally restricted cannabinoid type-1 receptor (CB1R) inverse agonist, in a streptozotocin-induced type-1 diabetes nephropathy mouse model.Methods: Diabetes was induced in 8-week-old C57BL6/J male mice via intraperitoneal injection of streptozotocin (45 mg/kg/day for 5 days); nondiabetic controls received citrate buffer. Diabetic mice were randomized to 3 groups based on blood glucose, polyuria, and albuminuria, and administered daily oral doses for 28-days of INV-202 at 0.3 or 3 mg/kg or vehicle.Results: INV-202 did not affect body weight but decreased kidney weight compared with the vehicle group. While polyuria was unaffected by INV-202 treatment, urinary urea (control 30.77 ± 14.93; vehicle 189.81 ± 31.49; INV-202 (0.3 mg/kg) 127.76 ± 20; INV-202 (3 mg/kg) 93.70 ± 24.97 mg/24h) and albumin (control 3.06 ± 0.38; vehicle 850.08 ± 170.50; INV-202 (0.3 mg/kg) 290.65 ± 88.70; INV-202 (3 mg/kg) 111.29 ± 33.47 µg/24h) excretion both decreased compared with vehicle-treated diabetic mice. Compared with the vehicle group, there was a significant improvement in the urinary albumin to creatinine ratio across INV-202 groups. Regardless of the dose, INV-202 significantly reduced angiotensin II excretion in diabetic mice. The treatment also decreased Agtr1a renal expression in a dose-dependent manner. Compared with nondiabetic controls, the glomerular filtration rate was increased in the vehicle group and significantly decreased by INV-202 at 3 mg/kg. While the vehicle group showed a significant loss in the mean number of podocytes per glomerulus, INV-202 treatment limited podocyte loss in a dose-dependent manner. Moreover, in both INV-202 groups, expression of genes coding for podocyte structural proteins nephrin (Nphs1), podocin (Nphs2), and podocalyxin (Pdxl) were restored to levels similar to nondiabetic controls. INV-202 partially limited the proximal tubular epithelial cell (PTEC) hyperplasia and normalized genetic markers for PTEC lesions. INV-202 also reduced expression of genes contributing to oxidative stress (Nox2, Nox4, and P47phox) and inflammation (Tnf). In addition, diabetes-induced renal fibrosis was significantly reduced by INV-202.Conclusions: INV-202 reduced glomerular injury, preserved podocyte structure and function, reduced injury to PTECs, and ultimately reduced renal fibrosis in a streptozotocin-induced diabetic nephropathy mouse model. These results suggest that INV-202 may represent a new therapeutic option in the treatment of diabetic kidney disease

Association of liver steatosis with lipid oversecretion and hypotriglyceridaemia in C57BL/6j mice fed trans-10, cis-12-linoleic acid

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Association of liver steatosis with lipid oversecretion and hypotriglyceridaemia in C57BL/6j mice fed trans-10, cis-12-linoleic acid

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