ABSTRACT: The obese, insulin resistant state is characterized by impairments in lipid metabolism. Dietary polyphenols might improve these deteriorations. We have previously shown that 3-days supplementation of combined Epigallocatechin-gallate and Resveratrol (E+R) increased energy expenditure, which was accompanied by improved metabolic flexibility after a high-fat mixed-meal (HFMM) in men. The present study aimed to investigate whether these short-term effects translate into longer-term improvement of insulin sensitivity and lipid metabolism. In this randomized, double-blind study, 42 overweight subjects (21 male, 38±2 yrs, BMI 29.7±0.5 kg/m2, HOMA-IR 2.1±0.2) received either E+R (300 and 80 mg/d, respectively) or placebo (PLA) for 12 weeks (3 months). Before (t0) and after (t3) intervention, tissue-specific insulin sensitivity was assessed by a hyperinsulinemic-euglycemic clamp with stable isotope infusion. Fasting and postprandial (HFMM) lipid metabolism was assessed using indirect calorimetry and blood sampling. Adipose tissue and skeletal muscle lipolysis was measured using microdialysis in men and skeletal muscle biopsies were collected to assess mitochondrial function and gene expression alterations via microarray analysis. E+R supplementation increased fasting (P=0.06) and postprandial (P=0.03) fat oxidation but did not alter energy expenditure compared to PLA. This was accompanied by an E+R-induced increase in oxidative capacity in permeabilized muscle fibers (p<0.05). Moreover, E+R supplementation attenuated the increase in plasma triacylglycerol concentration that was observed in the PLA group (AUC, p<0.05), and tended to decrease visceral fat mass (P=0.09). Finally, insulin-stimulated glucose disposal and suppression of endogenous glucose production were not affected by E+R supplementation. 12 weeks E+R supplementation increased whole-body fat oxidation and skeletal muscle oxidative capacity, but this did not translate into increased tissue-specific insulin sensitivity in overweight and obese subjects. To identify pathways that may underlie the E+R-induced improvement of skeletal muscle mitochondrial capacity, we performed microarray analysis on skeletal muscle biopsies (vastus lateralis muscle), collected before and after 12-weeks E+R or PLA treatment. Gene Set Enrichment Analysis (GSEA) indicated that the most upregulated pathways after E+R supplementation were related to the citric acid cycle and respiratory electron transport chain, while pathways related to carbohydrate metabolism were upregulated in the PLA group. In this randomized, double-blind placebo-controlled, parallel intervention trial, subjects received either a combination of E+R supplements (INTV, 282 mg/d and 80 mg/d, respectively) or placebo (PLA, partly hydrolyzed microcrystalline cellulose-filled capsules) for a period of 12 weeks (3 months) to assess effects of E+R supplementation on tissue-specific insulin sensitivity (primary outcomes) and fasting and postprandial substrate metabolism (secondary outcomes). Skeletal muscle (m. vastus lateralis) biopsies were taken under local anesthesia during fasting conditions before (t0) and after the 12-weeks (t3) intervention period. Extraxted RNA was hybridized on HTA 2.0 Affymetrix arrays and microarray analysis was performed on paired sample sets for 27 subjects (p, PLA n = 14; E+R n = 13).
