Rôle de la phase amplificatrice de la sécrétion d’insuline dans le développement de l’obésité induite par une diète hautement calorique

Diabetes & Metabolism Volume 37, numéro 1S1 page A3 (mars 2011)

L. Vetterli, S. Carobbio, F. Frigerio, A. Gjinovci, P. Herrera, P. Maechler

Le glutamate, produit grâce à la glutamate déshydrogénase, participe à la phase amplificatrice de la sécrétion d’insuline. Nous avons généré une lignée de souris dont les cellules bêta-pancréatiques n’expriment plus cette enzyme (ßGlud1-/-) avec comme conséquence une réponse sécrétoire moindre (J.Biol.Chem. 2009, 284:921-9). Ici, nous avons testé la réponse à une diète hautement calorique de ces souris.
Matériels et méthodes :

Les souris contrôles et ßGlud1-/- ont reçu une diète enrichie en calories pendant 20 semaines. Ensuite, nous avons effectué des tests de tolérance au glucose ainsi que diverses mesures métaboliques. Après isolation des îlots pancréatiques, les réponses sécrétoires ont été testées au cours d’expériences de périfusions. L’expression de gènes a également été analysée sur différents tissus par PCR quantitative.

Résultats :

Après 20 semaines de diète riche en calories, les souris contrôles sont devenues obèses et pesaient nettement plus que les souris contrôles sous diète normale (45,2 g contre 35,3 g). Les souris ßGlud1-/- sur diète riche en calories ont maintenu un poids comparable à celui des souris contrôles sur diète normale et présentaient une masse graisseuse ainsi qu’une taille d’adipocytes moindres ; ceci malgré une prise de nourriture semblable. L’efficacité métabolique était diminuée chez les souris ßGlud1-/- comparativement aux souris contrôles (0,69 g/MJ contre 1,6 g/MJ). Les souris ßGlud1-/- présentaient un quotient respiratoire plus bas comparé aux contrôles, indiquant une oxydation lipidique plus élevée. En adéquation avec la préservation d’un phénotype non obèse les souris ßGlud1-/- n’ont pas développé d’intolérance au glucose. Finalement, la sécrétion d’insuline était nettement plus faible chez les souris ßGlud1-/- que chez les souris contrôles (- 80% à 11,8 mM glucose, - 59% à 22,8 mM glucose ; p<0.01).

Conclusion :

L’absence de glutamate déshydrogénase dans la cellule bêta-pancréatique limite la sécrétion d’insuline en empêchant le développement de la phase amplificatrice. La conséquence observée est une protection contre une obésité induite par la diète.

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Interaction between Testosterone and Growth Hormone on Whole-Body Protein Anabolism Occurs in the Liver
The Journal of Clinical Endocrinology & Metabolism   2011 Vol. 96 (4): 1060-1067     Vita Birzniece

Context:

GH and testosterone both exert protein-anabolic effects and may act synergistically. Liver and muscle are major sites of protein metabolism.

Objective:

Our objective was to determine whether the site of GH and testosterone interaction on protein metabolism is primarily hepatic or extrahepatic.

Design:

In this open-label randomized crossover study, the impact on whole-body protein metabolism of oral (solely hepatic testosterone exposure) and transdermal (systemic testosterone exposure) testosterone replacement in the presence or absence of GH was compared.

Patients and Intervention:

Eleven hypopituitary men with GH and testosterone deficiency were randomized to 2-wk treatments with transdermal testosterone (10 mg) or oral testosterone (40 mg), with or without GH replacement (0.6 mg/d). The dose of testosterone administered orally achieves physiological portal testosterone concentrations without spillover into the systemic circulation.

Main Outcome Measures:

Whole-body leucine turnover was measured, from which leucine rate of appearance (LRa), an index of protein breakdown, and leucine oxidation (Lox), a measure of irreversible protein loss, were estimated at the end of each treatment.

Results:

In the absence of GH, neither transdermal nor oral testosterone affected LRa or Lox. GH therapy significantly increased LRa, an effect equally reduced by transdermal and oral testosterone administration. GH replacement alone did not significantly change Lox, whereas addition of testosterone treatment reduced Lox, with the effect not significantly different between transdermal and oral testosterone.

Conclusions:

In the doses used, testosterone stimulates protein anabolism by reducing protein breakdown and oxidation only in the presence of GH. Because the net effect on protein metabolism during GH therapy is not different between systemic and solely hepatic testosterone administration, we conclude that the liver is the primary site of this hormonal interaction.

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Caffeinated Coffee Does Not Acutely Affect Energy Intake, Appetite, or Inflammation but Prevents Serum Cortisol Concentrations from Falling in Healthy Men
Anna Gavrieli         J. Nutr. April 1, 2011 vol. 141 no. 4 703-707

Our aim in this crossover study was to investigate the acute effects of caffeinated and decaffeinated coffee consumption on appetite feelings, energy intake, and appetite-, inflammation-, stress-, and glucose metabolism-related markers. Sixteen healthy men (age range, 21–39 y; BMI range, 19.7–28.6 kg/m2) received in a random order on 3 separate occasions a standard breakfast snack with 200 mL of either caffeinated coffee (3 mg caffeine/kg body weight), decaffeinated coffee, or water (control). Before intervention (−15 min) and at standard time points following breakfast consumption (0, 15, 30, 60, 90, 120, 150, and 180 min), participants recorded their appetite feelings and we collected blood samples for measurements of circulating glucose, insulin, cortisol, and appetite- and inflammation-related markers. At 180 min, participants consumed a meal ad libitum. The appetite-related ratings, the appetite plasma hormonal responses as well as the plasma glucose, serum insulin, and plasma and serum inflammatory marker responses did not show an overall intervention effect or a time x intervention interaction. Ad libitum energy intake did not differ among the 3 interventions. However, a significant intervention effect (P = 0.04) and a time x intervention interaction (P-interaction = 0.02) were found for serum cortisol; cortisol concentrations were significantly higher following the caffeinated coffee intervention, compared to control, at 60 min and thereafter. In conclusion, the usually consumed amount of caffeinated coffee does not have short-term effects on appetite, energy intake, glucose metabolism, and inflammatory markers, but it increases circulating cortisol concentrations in healthy men.

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Use of dietary supplements by cardiologists, dermatologists and orthopedists: report of a survey
Annette Dickinson, Andrew Shao, Nicolas Boyon and Julio C. Franco Nutrition Journal 2011, 10:20 doi:10.1186/1475-2891-10-20

Dietary supplements are regularly used by a majority of the American population, and usage by health professionals is also common. There is considerable interest in usage patterns within the population and in the reasons for using dietary supplements. The “Life…supplemented” Healthcare Professionals 2008 Impact Study (HCP Impact Study) surveyed usage of dietary supplements by physicians in three specialties: cardiology, dermatology, and orthopedics.

Methods

The HCP Impact Study was conducted online by Ipsos Public Affairs for the Council for Responsible Nutrition (CRN), a trade association of the dietary supplement industry. Respondents were 900 physicians, including 300 each from three specialties - cardiology, dermatology, and orthopedics.

Results

Fifty-seven percent of cardiologists said they use dietary supplements at least occasionally, as did 75% of dermatologists and 73% of orthopedists.
The product most commonly reported to be used was a multivitamin, but over 25% in each specialty said they used omega-3 fatty acids and over 20% said they used some botanical supplements. Regular dietary supplement use was reported by 37% of cardiologists, 59% of dermatologists, and 50% of orthopedists. Seventy-two percent of cardiologists, 66% of dermatologists, and 91% of orthopedists reported recommending dietary supplements to their patients. The primary reason given for recommending dietary supplements to patients was for heart health or lowering cholesterol for the cardiologists; benefits for skin, hair and nails for the dermatologists; and bone and joint health for the orthopedists.

Conclusions

Reported dietary supplement use was relatively common in this sample of physicians, and when they recommended dietary supplements to patients, they tended to do so for reasons related to their specialty.

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Effects of high-whey-protein intake and resistance training on renal, bone and metabolic parameters in rats
Virginia A. Aparicio British Journal of NutritionBritish Journal of Nutrition (2011), 105: 836-845

Consumption of high-protein (HP) diets is postulated to exert a negative influence on bone and renal health. However, no conclusive evidence has been presented related to this issue or to the potential protective action of resistance training on HP-induced systemic effects. We examined the effects of HP diet consumption on food intake, body-weight gain, body composition, and renal, bone and metabolic parameters of rats performing resistance training. A total of ninety-six adult male Wistar rats were randomly distributed in twelve experimental groups (n 8): normal-protein (10 %) or HP (45 %) diets, with or without resistance training, killed for experimental periods of 1, 2 or 3 months. Diets were based on a commercial whey protein hydrolysate. Consumption of HP diets and resistance training significantly affected food intake, body weight and body composition, as well as the plasma levels of total cholesterol, HDL-cholesterol and TAG. The buffering action of resistance training on such diet-induced alterations was especially evident in the levels of plasma TAG. Consumption of HP diets led to a considerable increase in kidney weight, urinary volume and acidity, as well as in the urinary excretion of Ca, with a parallel reduction in the urinary excretion of citrate (P < 0·05). No apparent deleterious effect on bone mineral content was found. In conclusion, consumption of HP diets caused alterations in renal health status and some metabolic parameters, but did not seem to affect bone status. Resistance training had a protective action against alterations of renal health status and some metabolic parameters such as plasma TAG.

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Habitual Intake of Guaraná and Metabolic Morbidities: An Epidemiological Study of an Elderly Amazonian Population
Cristina da Costa Krewer   Phytotherapy Research   Early View

The aim of the present study was to evaluate the associations of metabolic disorders and anthropometric and biochemical biomarkers of lipid, glucose and oxidative metabolism and the habitual ingestion of guaraná (Paullinia cupana, Mart. Var. sorbilis) by an elderly population residing in the Amazon Riverine region of the Maués municipality (Brazil). A case-controlled study was performed that included 637 elderly (≥60 years of age) patients classified as either those who habitually drank guaraná (GI, n = 421) or those who never drank guaraná (NG, n  = 239) based upon their self-reported intake of guaraná. Indeed, the prevalence of various metabolic disorders was associated with guaraná ingestion. The prevalence of hypertension, obesity and metabolic syndrome in the GI group was lower than the prevalence found in the NG group. The NG group exhibited lower systolic and diastolic blood pressure values. The males in the GI group exhibited a lower waist circumference, on average, than the circumference found in the NG group, whereas the females in the GI group had lower cholesterol (total and LDL-c) levels than the control cohort. Additionally, a significant association was found between lower levels of advanced oxidative protein product (AOPP) and habitual guaraná consumption. The results constitute the first epidemiological study to suggest a potentially protective effect of habitual guaraná ingestion against metabolic disorders in elderly subjects.

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The secular trend for grip strength in Canada and the United States
Irwin W. Silvermana Journal of Sports Sciences 28 February 2011

Worldwide, body weight has risen dramatically in recent decades, raising the question of whether there were concomitant changes in physical fitness. Past research with children and adolescents has shown that body weight and grip strength are positively correlated. Therefore, it was predicted that grip strength had increased on average in children and adolescents over the past four or five decades. To test this prediction, relevant data were extracted from 18 studies for males (N = 5676 in total) and 17 studies for females (N = 5489 in total). The studies were conducted in Canada and the United States from about 1966 on, with participants’ ages ranging from 6 through 19 years. Weighted least squares regression analyses showed that grip strength was significantly predicted by age but not by country. Male grip strength decreased significantly over the period covered, but the change was very small, accounting for far less than 1% of the variance in male grip strength. Discussion focuses on potential explanations for why grip strength did not change over time as predicted.

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