LPS-Enhanced Glucose-Stimulated Insulin Secretion Is Normalized by Resveratrol.

UNLABELLED: Low-grade inflammation is seen with obesity and is suggested to be a mediator of insulin resistance. The eliciting factor of low-grade inflammation is unknown but increased permeability of gut bacteria-derived lipopolysaccharides (LPS) resulting in endotoxemia could be a candidate. Here we test the effect of LPS and the anti-inflammatory compound resveratrol on glucose homeostasis, insulin levels and inflammation. Mice were subcutaneously implanted with osmotic mini pumps infusing either low-dose LPS or saline for 28 days. Half of the mice were treated with resveratrol delivered through the diet. LPS caused increased inflammation of the liver and adipose tissue (epididymal and subcutaneous) together with enlarged spleens and increased number of leukocytes in the blood. Resveratrol specifically reduced the inflammatory status in epididymal fat (reduced expression of TNFa and Il1b, whereas the increased macrophage infiltration was unaltered) without affecting the other tissues investigated. By LC-MS, we were able to quantitate resveratrol metabolites in epididymal but not subcutaneous adipose tissue. LPS induced insulin resistance as the glucose-stimulated insulin secretion during an oral glucose tolerance test was increased despite similar plasma glucose level resulting in an increase in the insulinogenic index (IGI; delta0-15insulin/delta0-15glucose) from 13.73 to 22.40 pmol/mmol (P < 0.001). This aberration in insulin and glucose homeostasis was normalized by resveratrol. IN CONCLUSION: Low-dose LPS enhanced the glucose-stimulated insulin secretion without affecting the blood glucose suggesting increased insulin resistance. Resveratrol restored LPS-induced alteration of the insulin secretion and demonstrated anti-inflammatory effects specifically in epididymal adipose tissue possibly due to preferential accumulation of resveratrol metabolites pointing towards a possible important involvement of this tissue for the effects on insulin resistance and insulin secretion.

Growth hormone signaling in muscle and adipose tissue of obese human subjects: associations with measures of body composition and interaction with resveratrol treatment.

CONTEXT: Growth hormone (GH) secretion is reduced in obesity, despite normal serum insulin-like growth factor I (IGF-1) levels, but the association between obesity and the GH signaling is unknown. Furthermore, SIRT1, an nicotinamide adenine dinucleotide-dependent protein deacetylase, reduces hepatic IGF-1 production in mice via blunting of GH-induced STAT5 signaling. OBJECTIVE: To study GH signaling in muscle and fat in obese subjects and the interaction with concomitant administration of the putative SIRT1 activator resveratrol, and to assess the effects of inhibiting or knocking down SIRT1 on GH regulated genes in vitro. DESIGN AND PARTICIPANTS: Twenty-four obese males were examined in a randomized, double blinded, parallel-group study with resveratrol or placebo treatment for 5 weeks followed by a GH bolus. Muscle and fat biopsies were collected before and after GH. Body composition was assessed by DEXA and MRI. MAIN OUTCOME MEASURE: (1) Effect of body composition and age on GH-stimulated STAT5b phosphorylation and IGF-1, SOCS2, and CISH mRNA in muscle and fat. (2) The impact of resveratrol treatment on GH activity. (3) Impact of inhibiting or knocking down SIRT1 on effects of GH in vitro. RESULTS: Significant GH-induced STAT5b phosphorylation in muscle and fat in obese subjects was recorded together with increased CISH and SOCS2 mRNA. GH-induced STAT5b phosphorylation in muscle correlated positively with age [r = 0.53, p < 0.01], but not with body composition. Resveratrol administration had no impact on body composition, serum IGF-1, or GH signaling in vivo, and SIRT1 knock down or inhibition did not affect GH signaling in vitro. CONCLUSION: (1) GH induced STAT5b phosphorylation is detectable in muscle and fat in adult males with simple obesity, but is not determined by body composition. (2) Resveratrol supplementation does not impact circulating IGF-1 levels or GH signaling in human muscle and fat. (3) Our data speak against a major impact of SIRT1on GH action in human subjects.

Ghrelin- and GH-induced insulin resistance: no association with retinol-binding protein-4.

OBJECTIVE: Supraphysiological levels of ghrelin and GH induce insulin resistance. Serum levels of retinol-binding protein-4 (RBP4) correlate inversely with insulin sensitivity in patients with type 2 diabetes. We aimed to determine whether ghrelin and GH affect RBP4 levels in human subjects. MATERIALS AND METHODS: To study GH-independent effects of ghrelin, seven hypopituitary men undergoing replacement therapy with GH and hydrocortisone were given ghrelin (5 pmol/kg per min) and saline infusions for 300 min in a randomized, double-blind, placebo-controlled, crossover design. Circulating RBP4 levels were measured at baseline and during a hyperinsulinemic-euglycemic clamp on both study days. To study the direct effects of GH, nine healthy men were treated with GH (2 mg at 2200 h) and placebo for 8 days in a randomized, double-blind, placebo-controlled, crossover study. Serum RBP4 levels were measured before and after treatment, and insulin sensitivity was measured by the hyperinsulinemic-euglycemic clamp technique. RESULTS: Ghrelin acutely decreased peripheral insulin sensitivity. Serum RBP4 concentrations decreased in response to insulin infusion during the saline experiment (mg/l): 43.2±4.3 (baseline) vs 40.4±4.2 (clamp), P<0.001, but this effect was abrogated during ghrelin infusion (mg/l): 42.4±4.5 (baseline) vs 42.9±4.7 (clamp), P=0.73. In healthy subjects, serum RBP4 levels were not affected by GH administration (mg/l): 41.7±4.1 (GH) vs 43.8±4.6 (saline), P=0.09, although GH induced insulin resistance. CONCLUSIONS: i) Serum RBP4 concentrations decrease in response to hyperinsulinemia, ii) ghrelin abrogates the inhibitory effect of insulin on circulating RBP4 concentrations, and iii) ghrelin as well as GH acutely induces insulin resistance in skeletal muscle without significant changes in circulating RBP4 levels.

High-dose resveratrol supplementation in obese men: an investigator-initiated, randomized, placebo-controlled clinical trial of substrate metabolism, insulin sensitivity, and body composition.

Obesity, diabetes, hypertension, and hyperlipidemia constitute risk factors for morbidity and premature mortality. Based on animal and in vitro studies, resveratrol reverts these risk factors via stimulation of silent mating type information regulation 2 homolog 1 (SIRT1), but data in human subjects are scarce. The objective of this study was to examine the metabolic effects of high-dose resveratrol in obese human subjects. In a randomized, placebo-controlled, double-blinded, and parallel-group design, 24 obese but otherwise healthy men were randomly assigned to 4 weeks of resveratrol or placebo treatment. Extensive metabolic examinations including assessment of glucose turnover and insulin sensitivity (hyperinsulinemic euglycemic clamp) were performed before and after the treatment. Insulin sensitivity, the primary outcome measure, deteriorated insignificantly in both groups. Endogenous glucose production and the turnover and oxidation rates of glucose remained unchanged. Resveratrol supplementation also had no effect on blood pressure; resting energy expenditure; oxidation rates of lipid; ectopic or visceral fat content; or inflammatory and metabolic biomarkers. The lack of effect disagrees with persuasive data obtained from rodent models and raises doubt about the justification of resveratrol as a human nutritional supplement in metabolic disorders.