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Objective: Adipose tissue plays a key role in obesity-related metabolic dysfunction. MicroRNA (miRNA) are gene regulatory molecules involved in intercellular and inter-organ communication. It was hypothesized that miRNA levels in adipose tissue would change after gastric bypass surgery and that this would provide insights into their role in obesity-induced metabolic dysregulation., Methods: miRNA profiling (Affymetrix GeneChip miRNA 2.0 Array) of omental and subcutaneous adipose (n = 15 females) before and after gastric bypass surgery was performed., Results: One omental and thirteen subcutaneous adipose miRNAs were significantly differentially expressed after gastric bypass, including downregulation of miR-223-3p and its antisense relative miR-223-5p in both adipose tissues. mRNA levels of miR-223-3p targets NLRP3 and GLUT4 were decreased and increased, respectively, following gastric bypass in both adipose tissues. Significantly more NLRP3 protein was observed in omental adipose after gastric bypass (P = 0.02). Significant hypomethlyation of NLRP3 and hypermethylation of miR-223 were observed in both adipose tissues after gastric bypass. In subcutaneous adipose, significant correlations were observed between both miR-223-3p and miR-223-5p and glucose and between NLRP3 mRNA and protein levels and blood lipids., Conclusions: This is the first report detailing genome-wide miRNA profiling of omental adipose before and after gastric bypass, and it further highlights the association of miR-223-3p and the NLRP3 inflammasome with obesity., (© 2020 The Obesity Society.)

Obesity, particularly visceral adiposity, has been linked to mitochondrial dysfunction and increased oxidative stress, which have been suggested as mechanisms of insulin resistance. The mechanism(s) behind this remains incompletely understood. In this study, we hypothesized that mitochondrial complex II dysfunction plays a role in impaired insulin sensitivity in visceral adipose tissue of subjects with obesity. We obtained subcutaneous and visceral adipose tissue biopsies from 43 subjects with obesity (body mass index ≥ 30 kg/m 2 ) during planned bariatric surgery. Compared with subcutaneous adipose tissue, visceral adipose tissue exhibited decreased complex II activity, which was restored with the reducing agent dithiothreitol (5 mM) ( P < 0.01). A biotin switch assay identified that cysteine oxidative posttranslational modifications (OPTM) in complex II subunit A (succinate dehydrogenase A) were increased in visceral vs. subcutaneous fat ( P < 0.05). Insulin treatment (100 nM) stimulated complex II activity in subcutaneous fat ( P < 0.05). In contrast, insulin treatment of visceral fat led to a decrease in complex II activity ( P < 0.01), which was restored with addition of the mitochondria-specific oxidant scavenger mito-TEMPO (10 µM). In a cohort of 10 subjects with severe obesity, surgical weight loss decreased OPTM and restored complex II activity, exclusively in the visceral depot. Mitochondrial complex II may be an unrecognized and novel mediator of insulin resistance associated with visceral adiposity. The activity of complex II is improved by weight loss, which may contribute to metabolic improvements associated with bariatric surgery.

Objective: Extracellular microRNAs (miRNAs) represent functional biomarkers for obesity and related disorders; this study investigated plasma miRNAs in insulin resistance phenotypes in obesity., Methods: One hundred seventy-five miRNAs were analyzed in females with obesity (insulin sensitivity, n = 11; insulin resistance, n = 19; type 2 diabetes, n = 15) and without obesity (n = 12). Correlations between miRNA level and clinical parameters and levels of 15 miRNAs in a murine obesity model were investigated., Results: One hundred six miRNAs were significantly (adjusted P ≤ 0.05) different between controls and at least one obesity phenotype, including miRNAs with the following attributes: previously reported roles in obesity and altered circulating levels (e.g., miR-122, miR-192); known roles in obesity but no reported changes in circulating levels (e.g., miR-378a); and no current reported role in, or association with, obesity (e.g., miR-28-5p, miR-374b, miR-32). The miRNAs in the latter group were found to be associated with extracellular vesicles. Forty-eight miRNAs showed significant correlations with clinical parameters; stepwise regression retained let-7b, miR-144-5p, miR-34a, and miR-532-5p in a model predictive of insulin resistance (R 2  = 0.57, P = 7.5 × 10 -8 ). Both miR-378a and miR-122 were perturbed in metabolically relevant tissues in a murine model of obesity., Conclusions: This study expands on the role of extracellular miRNAs in insulin-resistant phenotypes of obesity and identifies candidate miRNAs not previously associated with obesity., (© 2017 The Obesity Society.)

Background: Epigenetic mechanisms provide an interface between environmental factors and the genome and are known to play a role in complex diseases such as obesity. These mechanisms, including DNA methylation, influence the regulation of development, differentiation and the establishment of cellular identity. Here we employ two approaches to identify differential methylation between two white adipose tissue depots in obese individuals before and after gastric bypass and significant weight loss. We analyse genome-wide DNA methylation data using (a) traditional paired t tests to identify significantly differentially methylated loci (Bonferroni-adjusted P  ≤ 1 × 10 -7 ) and (b) novel combinatorial algorithms to identify loci that differentiate between tissue types., Results: Significant differential methylation was observed for 3239 and 7722 CpG sites, including 784 and 1129 extended regions, between adipose tissue types before and after significant weight loss, respectively. The vast majority of these extended differentially methylated regions (702) were consistent across both time points and enriched for genes with a role in transcriptional regulation and/or development (e.g. homeobox genes). Other differentially methylated loci were only observed at one time point and thus potentially highlight genes important to adipose tissue dysfunction observed in obesity. Strong correlations ( r  > 0.75, P  ≤ 0.001) were observed between changes in DNA methylation (subcutaneous adipose vs omentum) and changes in clinical trait, in particular for CpG sites within PITX2 and fasting glucose and four CpG sites within ISL2 and HDL. A single CpG site (cg00838040, ATP2C2 ) gave strong tissue separation, with validation in independent subcutaneous ( n  = 681) and omental ( n  = 33) adipose samples., Conclusions: This is the first study to report a genome-wide DNA methylome comparison of subcutaneous abdominal and omental adipose before and after weight loss. The combinatorial approach we utilised is a powerful tool for the identification of methylation loci that strongly differentiate between these tissues. This study provides a solid basis for future research focused on the development of adipose tissue and its potential dysfunction in obesity, as well as the role DNA methylation plays in these processes.

Background: Environmental factors can influence obesity by epigenetic mechanisms. Adipose tissue plays a key role in obesity-related metabolic dysfunction, and gastric bypass provides a model to investigate obesity and weight loss in humans., Results: Here, we investigate DNA methylation in adipose tissue from obese women before and after gastric bypass and significant weight loss. In total, 485,577 CpG sites were profiled in matched, before and after weight loss, subcutaneous and omental adipose tissue. A paired analysis revealed significant differential methylation in omental and subcutaneous adipose tissue. A greater proportion of CpGs are hypermethylated before weight loss and increased methylation is observed in the 3' untranslated region and gene bodies relative to promoter regions. Differential methylation is found within genes associated with obesity, epigenetic regulation and development, such as CETP, FOXP2, HDAC4, DNMT3B, KCNQ1 and HOX clusters. We identify robust correlations between changes in methylation and clinical trait, including associations between fasting glucose and HDAC4, SLC37A3 and DENND1C in subcutaneous adipose. Genes investigated with differential promoter methylation all show significantly different levels of mRNA before and after gastric bypass., Conclusions: This is the first study reporting global DNA methylation profiling of adipose tissue before and after gastric bypass and associated weight loss. It provides a strong basis for future work and offers additional evidence for the role of DNA methylation of adipose tissue in obesity.

The explanation for the rapid improvement in insulin resistance after Roux-en Y gastric bypass (RYGB) may involve mechanisms additional to caloric restriction and improvements in peripheral glucose disposal. 8 severely obese patients underwent a 6-day very low calorie diet (VLCD) (456 kcal/day) followed 1-3 weeks later by RYGB. Insulin resistance was measured by short intravenous insulin tolerance test (IVITT) and by homeostasis model assessment (HOMA) before and again 6 days after the VLCD and after RYGB. In a group of 24 matched patients, HOMA assessments were made before and six days after RYGB. HOMA-IR fell significantly from 6.84.9 to 4.32.9 (p < 0.05) following VLCD, but this was less than the subsequent fall following RYGB (6.8 ± 4.9 to 1.50.4, p < 0.01). Control patients who underwent RYGB alone, reduced their HOMA-IR to 1.50.9 following the operation which was not significantly different from the VLCD then RYGB group. Following VLCD, IVITT showed no significant change. However, 6 days after RYGB, IVITT showed worsened insulin induced glucose uptake (p < 0.05). Patients undergoing VLCD over six days had a reduction in HOMA-IR which was half that of patients undergoing RYGB. Patients who underwent both VLCD and RYGB had a total reduction in HOMA similar to those who underwent the RYGB alone. In contrast, IVITT showed a worsening in insulin induced glucose disposal following RYGB, which suggests worsening peripheral insulin resistance. This study supports the hypothesis that mechanisms other than caloric restriction are involved in the acute improvement in HOMA-IR following RYGB.

Background: Severely obese type 2 diabetics who undergo Roux-en Y gastric bypass surgery have significant improvements in glycaemic control. Little work has been undertaken to establish the independent predictors of such resolution or to develop a predictive model. The aim of this study was to develop a mathematical model and establish independent predictors for the resolution of diabetes., Methods: A consecutive sample of 130 severely obese type 2 diabetics who underwent gastric bypass surgery for weight loss from November 1997 to May 2007 with prospective pre-operative documentation of biochemical and clinical measurements was followed up over 12 months. Logistic discrimination analysis was undertaken to identify those variables with independent predictive value and to develop a predictive model for resolution of type 2 diabetes. Consecutive samples of 130 patients with body mass index (BMI) ≥ 35 with type 2 diabetes were selected. One hundred and twenty-seven patients completed the study with a sufficient data set. Patients were deemed unresolved if (1) diabetic medication was still required after surgery; (2) if fasting plasma glucose (FPG) remained >7 mmol/L; or (3) HbA1c remained >7%., Results: Resolution of diabetes was seen in 84%, while diabetes remained but was improved in 16% of patients. Resolution was rapid and sustained with 74% of those on medication before surgery being able to discontinue this by the time of discharge 6 days following surgery. Five pre-operative variables were found to have independent predictive value for resolution of diabetes, including BMI, HbA1c, FPG, hypertension and requirement for insulin. Two models have been proposed for prediction of diabetes resolution, each with 86% correct classification in this cohort of patients., Conclusions: Type 2 diabetes resolves in a very high percentage of patients undergoing gastric bypass surgery for severe obesity. The key predictive variables include pre-operative BMI, HbA1c, FPG, the presence of hypertension and diabetic status.