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Impaired adipose tissue (AT) function closely associates with obesity, type 2 diabetes and nonalcoholic fatty liver disease (NAFLD) . Mitochondrial oxidative phosphorylation (OXPHOS) capacity of AT improves after weight loss surgery. However, it is not clear if the improvement is affected by the presence of NAFLD before surgery. We examined 52 severely obese people exhibiting no histological liver disease (OBE_CON) , simple steatosis (OBE_NAFL) or steatohepatitis (OBE_NASH) before (0 weeks) , 12 and 52 weeks after bariatric surgery. Whole-body insulin sensitivity was measured by hyperinsulinemic euglycemic clamps. OXPHOS capacity of subcutaneous AT was assessed by high-resolution respirometry. Transcript levels of TNFα in AT were quantified by RT-PCR. Before surgery, OBE_NASH presented with lower insulin sensitivity and higher HbA1c compared to OBE_CON and OBE_NAFL (all p In conclusion, in severe obesity, weight loss-related improvements in AT OXPHOS capacity may be mediated to a great extent by reduced AT inflammation in people without liver disease; however, with pre-surgery manifestation of NASH and worsening of metabolic control, residual systemic subclinical inflammation may attenuate the improvement of AT OXPHOS capacity after bariatric surgery. Disclosure S.Kahl: None. G.Heilmann: None. I.Esposito: None. M.Schlensak: None. M.Roden: Advisory Panel; Eli Lilly and Company, Research Support; Boehringer Ingelheim International GmbH, Nutricia, Speaker's Bureau; Novo Nordisk. K.Strassburger: None. S.Gancheva: None. N.Saatmann: None. C.Granata: None. C.Herder: Research Support; Sanofi. K.Pafili: None. J.Puetzer-furmanczak: None. T.Sarabhai: None. Funding German Federal Ministry of Health; Ministry of Culture and Science of the State North Rhine-Westphalia;German Federal Ministry of Education and Research;European Funds for Regional Development (EFRE-0400191) ;EUREKA Eurostars-2 (E!113230DIA-PEP) ;German Science Foundation (CRC/SFB1116/2 B12; RTG/GRK 2576 vivid, Project 3) ;Schmutzler Stiftung

Adipose dysfunction may drive the development of insulin resistance, type 2 diabetes (T2D) and nonalcoholic (NA) fatty liver disease (NAFLD), comprising NA fatty liver and steatohepatitis (NAFL and NASH). Possible underlying mechanism comprise impaired lipid storage or mitochondrial oxidation favoring increased fatty acid flux to other tissues. Thus, we examined subcutaneous (SAT) and visceral adipose tissue (VAT) mitochondrial capacity in humans with different degrees of insulin resistance and histologically proven NAFLD. Obese people without NAFL (OBE-CON, n=20, 38±8 years, body mass index 53±6 kg/m2, 10% T2D), with NAFL (OBE-NAFL, n=20, 40±8 years, 51±5 kg/m2, 25% T2D) or NASH (OBE-NASH, n=20, 42±10 years, 51±6 kg/m2, 40% T2D) underwent metabolic phenotyping and tissue biopsies. O2 flux rates from different substrates were measured with high resolution respirometry in SAT and VAT. In VAT, maximal uncoupled respiration was lower in OBE-NAFL (least square means (LSM): 0.46 pmol*mg wet weight–1*s–1 [95% confidence interval 0.21;0.71], p In conclusion, oxidative capacity is downregulated in VAT, but not in SAT of obese humans with NAFLD, which may be related to the degree of insulin resistance. Disclosure K. Pafili: None. M. Schlensak: None. M. Roden: Advisory Panel; Self; Allergan plc, Bristol-Myers Squibb Company, Novo Nordisk A/S, Research Support; Self; Boehringer Ingelheim International GmbH, Danone Nutricia, Sanofi-Aventis Deutschland GmbH. S. Kahl: None. D. Pesta: None. K. Strassburger: None. L. Mastrototaro: None. J. Puetzer-furmanczak: None. B. Dewidar: None. T. Sarabhai: None. I. Esposito: None.

Weight loss-induced improvement in insulin sensitivity (IS) has been related to enhanced muscle energy metabolism. Thus, we hypothesized that weight loss due to bariatric surgery may induce epigenomic changes, which in turn modify mitochondrial function and intracellular lipids. We previously reported that IS fails to improve at 2 weeks (2 w), but then continuously increases until 52 weeks (52 w) after surgery. Now, we monitored muscle mitochondrial function and lipid intermediates in 49 obese humans (OBE; 40±10 years, BMI 51±7 kg/m2) before and for 52 w after bariatric surgery. Genome-wide gene expression and DNA methylation were analyzed in a subgroup of 16 OBE. Initial weight loss increases muscle oxidative capacity by 11% at 2 w, but transient elevation of certain muscle diacylglycerols resulting from unrestrained adipose lipolysis prevents from rapid improvement in IS. At 52 w, both mitochondrial function and intracellular lipids are comparable to lean humans. Acute alterations in expression of 1287 genes involved primarily in mitochondrial function, transcriptional regulation, protein transport, fatty acid metabolism and inflammatory processes, but not changes in DNA methylation, underlie the transient upregulation of mitochondrial function and lipolysis. At 52 w, 1091CpGs are differentially methylated, which relates to improved IS. Specifically, epigenetic alterations at 52 w in FTO gene, encoding an α-ketoglutarate dependent dioxygenase, and TOMM7 gene, encoding a translocase of the outer mitochondrial membrane, contribute to reprogramming transient changes in mRNA expression at 2 w. In conclusion, initial metabolic changes after weight loss induce epigenetic modification of genes involved in muscle energy metabolism, which in turn leads to long-term beneficial changes in gene expression. Disclosure S. Gancheva: None. M. Ouni: None. C. Koliaki: None. T. Jelenik: None. D.F. Markgraf: None. J. Szendroedi: None. M. Schlensak: None. A. Schuermann: None. M. Roden: Speaker's Bureau; Self; Boehringer Ingelheim GmbH. Research Support; Self; Boehringer Ingelheim GmbH. Consultant; Self; Poxel SA. Research Support; Self; Danone Nutricia Early Life Nutrition, GlaxoSmithKline plc., Nutricia Advanced Medical Nutrition, Sanofi.