Tissue-specific Insulin Sensitivity Research Articles

Tissue-specific inflammation and insulin sensitivity in subjects with obesity

Obesity is associated with low-grade inflammation and insulin resistance (IR). The contribution of adipose tissue (AT) and hepatic inflammation to IR remains unclear. We conducted a study across three cohorts to investigate this relationship.The first cohort consists of six women with normal weight and twenty with obesity. In women with obesity, we found an upregulation of inflammatory markers in subcutaneous and visceral adipose tissue, isolated AT macrophages, and the liver, but no linear correlation with tissue-specific insulin sensitivity. In the second cohort, we studied 24 women with obesity in the upper vs lower insulin sensitivity quartile. We demonstrated that several omental and mesenteric AT inflammatory genes and T cell-related pathways are upregulated in IR, independent of BMI. The third cohort consists of 23 women and 18 men with obesity, studied before and one year after bariatric surgery. Weight loss following surgery was associated with downregulation of multiple immune pathways in subcutaneous AT and skeletal muscle, alongside notable metabolic improvements.Our results show that obesity is characterised by systemic and tissue-specific inflammation. Subjects with obesity and IR show a more pronounced inflammation phenotype, independent of BMI. Bariatric surgery-induced weight loss is associated with reduced inflammation and improved metabolic health.

Body composition and body fat distribution in tissue-specific insulin resistance and in response to a 12-week isocaloric dietary macronutrient intervention

BackgroundBody composition and body fat distribution are important predictors of cardiometabolic diseases. The etiology of cardiometabolic diseases is heterogenous, and partly driven by inter-individual differences in tissue-specific insulin sensitivity.ObjectivesTo investigate (1) the associations between body composition and whole-body, liver and muscle insulin sensitivity, and (2) changes in body composition and insulin sensitivity and their relationship after a 12-week isocaloric diet high in mono-unsaturated fatty acids (HMUFA) or a low-fat, high-protein, high-fiber (LFHP) diet.MethodsThis subcohort analysis of the PERSON study includes 93 individuals (53% women, BMI 25–40 kg/m2, 40–75 years) who participated in this randomized intervention study. At baseline and after 12 weeks of following the LFHP, or HMUFA diet, we performed a 7-point oral glucose tolerance test to assess whole-body, liver, and muscle insulin sensitivity, and whole-body magnetic resonance imaging to determine body composition and body fat distribution. Both diets are within the guidelines of healthy nutrition.ResultsAt baseline, liver fat content was associated with worse liver insulin sensitivity (β [95%CI]; 0.12 [0.01; 0.22]). Only in women, thigh muscle fat content was inversely related to muscle insulin sensitivity (-0.27 [-0.48; -0.05]). Visceral adipose tissue (VAT) was inversely associated with whole-body, liver, and muscle insulin sensitivity. Both diets decreased VAT, abdominal subcutaneous adipose tissue (aSAT), and liver fat, but not whole-body and tissue-specific insulin sensitivity with no differences between diets. Waist circumference, however, decreased more following the LFHP diet as compared to the HMUFA diet (-3.0 vs. -0.5 cm, respectively). After the LFHP but not HMUFA diet, improvements in body composition were positively associated with improvements in whole-body and liver insulin sensitivity.ConclusionsLiver and muscle insulin sensitivity are distinctly associated with liver and muscle fat accumulation. Although both LFHP and HMUFA diets improved in body fat, VAT, aSAT, and liver fat, only LFHP-induced improvements in body composition are associated with improved insulin sensitivity.Trial registrationNCT03708419 (clinicaltrials.gov).

MTORC1 and SGLT2 Inhibitors-A Therapeutic Perspective for Diabetic Cardiomyopathy.

Diabetic cardiomyopathy is a critical diabetes-mediated co-morbidity characterized by cardiac dysfunction and heart failure, without predisposing hypertensive or atherosclerotic conditions. Metabolic insulin resistance, promoting hyperglycemia and hyperlipidemia, is the primary cause of diabetes-related disorders, but ambiguous tissue-specific insulin sensitivity has shed light on the importance of identifying a unified target paradigm for both the glycemic and non-glycemic context of type 2 diabetes (T2D). Several studies have indicated hyperactivation of the mammalian target of rapamycin (mTOR), specifically complex 1 (mTORC1), as a critical mediator of T2D pathophysiology by promoting insulin resistance, hyperlipidemia, inflammation, vasoconstriction, and stress. Moreover, mTORC1 inhibitors like rapamycin and their analogs have shown significant benefits in diabetes and related cardiac dysfunction. Recently, FDA-approved anti-hyperglycemic sodium-glucose co-transporter 2 inhibitors (SGLT2is) have gained therapeutic popularity for T2D and diabetic cardiomyopathy, even acknowledging the absence of SGLT2 channels in the heart. Recent studies have proposed SGLT2-independent drug mechanisms to ascertain their cardioprotective benefits by regulating sodium homeostasis and mimicking energy deprivation. In this review, we systematically discuss the role of mTORC1 as a unified, eminent target to treat T2D-mediated cardiac dysfunction and scrutinize whether SGLT2is can target mTORC1 signaling to benefit patients with diabetic cardiomyopathy. Further studies are warranted to establish the underlying cardioprotective mechanisms of SGLT2is under diabetic conditions, with selective inhibition of cardiac mTORC1 but the concomitant activation of mTORC2 (mTOR complex 2) signaling.

The effect of weight loss on whole-body and tissue-specific insulin sensitivity and hepatic lipid content and composition: SWEET substudy.

This study (1) investigated the effect of weight loss on whole-body and tissue-specific insulin sensitivity and on intrahepatic lipid (IHL) content and composition and (2) investigated the association between weight-loss-induced changes in insulin sensitivity and IHL content in individuals with overweight or obesity. In this secondary analysis of the European SWEET project, 50 adults (age 18-65 years) with overweight or obesity (BMI ≥ 25 kg/m2 ) followed a low-energy diet (LED) for 2 months. At baseline and after the LED, body composition (dual-energy x-ray absorptiometry), IHL content and composition (proton magnetic resonance spectroscopy), whole-body insulin sensitivity (Matsuda index), muscle insulin sensitivity index (MISI), and hepatic insulin resistance index (HIRI) were determined (7-point oral glucose tolerance test). The LED reduced body weight (p < 0.001). This was accompanied by increased Matsuda index and reduced HIRI (both p < 0.001) but no change in MISI (p = 0.260). Weight loss decreased IHL content (mean [SEM], 3.9% [0.7%] vs. 1.6% [0.5%], p < 0.001) and the hepatic saturated fatty acid fraction (41.0% [1.5%] vs. 36.6% [1.9%], p = 0.039). The reduced IHL content was associated with an improvement in HIRI (r = 0.402, p = 0.025). Weight loss decreased IHL content and the hepatic saturated fatty acid fraction. The decrease in IHL content was associated with weight-loss-induced improvement in hepatic insulin sensitivity in individuals with overweight or obesity.

1579-P: Impact of Adipose Tissue Insulin Sensitivity on Hepatic Insulin Sensitivity Preservation in Longitudinal Observation of Patients with NAFLD

Hepatic insulin resistance associated with NAFLD is a major pathogenesis of type 2 diabetes and its complications. In addition to reducing lipids in the liver, identifying the factors that may preserve hepatic insulin sensitivity (H-IS) is crucial. In this study, we investigated the factors that may preserve H-IS in patients with NAFLD in longitudinal observations. Comprehensively, putative biomarkers in blood and urine, body composition, tissue-specific lipid accumulation and insulin sensitivity by 1H-MRS and hyperinsulinemic euglycemic clamp, respectively, and pathological diagnosis using liver biopsy were assessed in patients with NAFLD (n=62) at baseline. After more than one year of general treatment, consented 36 patients (average age 51.3±11.2, men n=21, diabetes n=23) were subjected to the same assessment as baseline. To investigate the indices associated with H-IS, all indices were compared between upper and lower one third patients of Δ% suppression of endogenous glucose production (EGP) (+11.5±4.0 vs. -10.9±5.1%, respectively). As results, body weight, fasting plasma glucose, HbA1c, muscle and adipose tissue insulin sensitivity, visceral fat, and adiponectin levels were significantly improved in improved H-IS group. Interestingly, Δhepatic lipid content or fibrosis index was not different between the improved and worsened H-IS groups. Furthermore, simple regression analysis with Δ% suppression of EGP and all indices revealed that Δ% suppression of free fatty acid, visceral fat area, and adiponectin levels were significantly associated with Δ% suppression of EGP. Multiple regression analysis with Δ% suppression of EGP and these three indices showed that only Δ% suppression of free fatty acid significantly associated with Δ% suppression of EGP. Taken together, not only lipid volume but also the quality of accumulated lipid is important to preserve hepatic insulin sensitivity in patients with NAFLD. Disclosure F.Shigiyama: None. S.Hiruma: None. N.Kumashiro: Research Support; Terumo Corporation, LifeScan Diabetes Institute, Sumitomo Dainippon Pharma Co., Ltd., Speaker's Bureau; Daiichi Sankyo, Novo Nordisk.

1566-P: The TM6SF2 rs58542926 Polymorphism Dissociates Hepatocellular Lipids from Insulin Resistance in Recent-Onset Type 2 Diabetes

Increased hepatocellular lipid content (HCL) is generally linked to insulin resistance, which contributes to greater risk of type 2 diabetes and cardiovascular complications. Conversely, a single-nucleotide polymorphism (TM6SF2EK; rs58542926) in the transmembrane 6 superfamily member 2 gene has been associated with nonalcoholic fatty liver disease (NAFLD), but lower cardiovascular risk. Thus, this case-control study tested the role of this polymorphism for tissue-specific insulin sensitivity during the early course of diabetes. Males with recent-onset type 2 diabetes with (TM6SF2EK: n=16) or without (TM6SF2EE: n=16) the heterozygous TM6SF2 polymorphism of similar age and BMI, underwent Botnia-clamps with [6,6-2H2]glucose to measure whole-body, hepatic and adipose tissue insulin sensitivity. HCL and liver fibrosis were assessed with 1H-magnetic resonance spectroscopy and non-invasive tests (FIB4, APRI, AST/ALT), respectively. A subset of both groups (n=24) was re-evaluated after 5 years. Despite doubled HCL, TM6SF2EK had similar hepatic and adipose tissue insulin sensitivity and even 27% higher whole-body insulin sensitivity than TM6SF2EE. The novel diabetes endotypes were equally distributed among both groups. After 5 years, whole-body insulin sensitivity, HCL and liver fibrosis indices were similar, while adipose tissue insulin sensitivity decreased by 87% and 55% both in TM6SF2EK and TM6SF2EE and circulating triacylglycerol increased in TM6SF2EE only. The TM6SF2 gene polymorphism rs58542926 dissociates ectopic fat content from insulin resistance in recent-onset type 2 diabetes, which is however attenuated by disease duration. This suggests that diabetes-related metabolic alterations dominate over the effects of the TM6SF2 gene polymorphism during the early course of diabetes and NAFLD. Disclosure K.Bódis: None. R.Guthoff: Other Relationship; Alimera, Bayer Inc., Novartis, Allergan. V.Schrauwen-hinderling: None. H.Al-hasani: None. V.Burkart: None. J.Szendroedi: None. R.Wagner: Advisory Panel; Daiichi Sankyo, Speaker's Bureau; Novo Nordisk, Sanofi. D.F.Markgraf: Employee; Boehringer Ingelheim Pharma GmbH&amp;Co.KG. M.Roden: Advisory Panel; Eli Lilly and Company, Consultant; TARGET PharmaSolutions, Inc., Research Support; Boehringer-Ingelheim, Novo Nordisk, Novartis, Sanofi. M.Bombrich: None. M.Schön: None. B.Knebel: None. O.P.Zaharia: None. G.J.Bönhof: None. Y.Karusheva: None. Y.Kupriyanova: None. J.Kotzka: None.

A Short-Term High-Fat Diet Worsens Insulin Sensitivity with Changes in Metabolic Parameters in Non-Obese Japanese Men.

A short-term high-calorie high-fat diet (HCHFD) impairs insulin sensitivity in non-obese South Asian but not Caucasian men; however, the effect of short-term HCHFD on insulin sensitivity in East Asians is unknown. We recruited 21 healthy non-obese Japanese men to evaluate metabolic parameters and gut microbiota before and after 6-day HCHFD consisting of a regular diet plus a 45% energy excess with dairy fat supplementation. We evaluated tissue-specific insulin sensitivity and metabolic clearance rate of insulin (MCRI) using a two-step hyperinsulinemic euglycemic clamp, glucose tolerance using the glucose tolerance test, and measured ectopic fat in muscle and the liver using ¹H-magnetic resonance spectroscopy. The primary outcome of this study was insulin sensitivity measured by the clamp study. The secondary/exploratory outcomes were other metabolic changes. After HCHFD, levels of circulating lipopolysaccharide binding protein (LBP), a marker of endotoxemia, increased by 14%. In addition, intramyocellular lipid levels in the tibialis anterior and soleus and intrahepatic lipid levels increased by 47%, 31%, and 200%, respectively. Insulin sensitivity decreased by 4% in muscle and 8% in liver. However, even with reduced insulin sensitivity, glucose metabolism was maintained by increased serum insulin concentrations due to lower MCRI and higher endogenous insulin secretion during the clamp. Glucose levels during the meal tolerance test were comparable before and after HCHFD. In conclusion, short-term HCHFD impaired insulin sensitivity in the muscle and livers of non-obese Japanese men with increased LBP and ectopic fat accumulation. Elevated insulin levels from modulated insulin secretion and clearance might contribute to the maintenance of normal glucose metabolism during the clamp and meal tolerance test.

Effects of TM6SF2 rs58542926 polymorphism on hepatocellular lipids and insulin resistance in early type 2 diabetes

Background and aimsIncreased hepatocellular lipid content (HCL) is linked to insulin resistance, risk of type 2 diabetes and related complications. Conversely, a single-nucleotide polymorphism (TM6SF2EK; rs58542926) in the transmembrane 6 superfamily member 2-gene has been associated with nonalcoholic fatty liver disease (NAFLD), but lower cardiovascular risk. This case-control study tested the role of this polymorphism for tissue-specific insulin sensitivity during early course of diabetes. Methods and resultsMales with recent-onset type 2 diabetes with (TM6SF2EK: n = 16) or without (TM6SF2EE: n = 16) the heterozygous TM6SF2-polymorphism of similar age and body mass index, underwent Botnia-clamps with [6,6-2H2]glucose to measure whole-body-, hepatic- and adipose tissue-insulin sensitivity. HCL was assessed with 1H-magnetic-resonance-spectroscopy. A subset of both groups (n = 24) was re-evaluated after 5 years. Despite doubled HCL, TM6SF2EK had similar hepatic- and adipose tissue-insulin sensitivity and 27% higher whole-body-insulin sensitivity than TM6SF2EE. After 5 years, whole-body-insulin sensitivity, HCL were similar between groups, while adipose tissue-insulin sensitivity decreased by 87% and 55% within both groups and circulating triacylglycerol increased in TM6SF2EE only. ConclusionsThe TM6SF2-polymorphism rs58542926 dissociates HCL from insulin resistance in recent-onset type 2 diabetes, which is attenuated by disease duration. This suggests that diabetes-related metabolic alterations dominate over effects of the TM6SF2-polymorphism during early course of diabetes and NAFLD.

Alpha-linolenic acid modulates systemic and adipose tissue-specific insulin sensitivity, inflammation, and the endocannabinoid system in dairy cows

Metabolic disorders are often linked to alterations in insulin signaling. Omega-3 (n-3) fatty acids modulate immunometabolic responses; thus, we examined the effects of peripartum n-3 on systemic and adipose tissue (AT)-specific insulin sensitivity, immune function, and the endocannabinoid system (ECS) in dairy cows. Cows were supplemented peripartum with saturated fat (CTL) or flaxseed supplement rich in alpha-linolenic acid (ALA). Blood immunometabolic biomarkers were examined, and at 5–8 d postpartum (PP), an intravenous glucose-tolerance-test (GTT) and AT biopsies were performed. Insulin sensitivity in AT was assessed by phosphoproteomics and proteomics. Peripartum n-3 reduced the plasma concentrations of Interleukin-6 (IL-6) and IL-17α, lowered the percentage of white blood cells PP, and reduced inflammatory proteins in AT. Systemic insulin sensitivity was higher in ALA than in CTL. In AT, the top canonical pathways, according to the differential phosphoproteome in ALA, were protein-kinase-A signaling and insulin-receptor signaling; network analysis and immunoblots validated the lower phosphorylation of protein kinase B (Akt), and lower abundance of insulin receptor, together suggesting reduced insulin sensitivity in ALA AT. The n-3 reduced the plasma concentrations of ECS-associated ligands, and lowered the abundances of cannabinoid-1-receptor and monoglycerol-lipase in peripheral blood mononuclear cells PP. Peripartum ALA supplementation in dairy cows improved systemic insulin sensitivity and immune function, reduced ECS components, and had tissue-specific effects on insulin-sensitivity in AT, possibly counter-balancing the systemic responses.

Circulating and adipose tissue immune cells in tissue-specific insulin resistance in humans with overweight and obesity.

A proinflammatory adipose tissue (AT) microenvironment and systemic low-grade inflammation may differentially affect tissue-specific insulin sensitivity. This study investigated the relationships of abdominal subcutaneous AT (aSAT) and circulating immune cells, aSAT gene expression, and circulating inflammatory markers with liver and skeletal muscle insulin sensitivity in people with overweight and obesity. Individuals with overweight and obesity from the PERSonalized Glucose Optimization Through Nutritional Intervention (PERSON) Study (n=219) and the Maastricht Study (replication cohort; n=1256) underwent a seven-point oral glucose tolerance test to assess liver and muscle insulin sensitivity, and circulating inflammatory markers were determined. In subgroups, flow cytometry was performed to identify circulating and aSAT immune cells, and aSAT gene expression was evaluated. The relative abundances of circulating T cells, nonclassical monocytes, and CD56dim CD16+ natural killer cells were inversely associated with liver, but not muscle, insulin sensitivity in the PERSON Study. The inverse association between circulating (classical) monocytes and liver insulin sensitivity was confirmed in the Maastricht Study. In aSAT, immune cell populations were not related to insulin sensitivity. Furthermore, aSAT gene expression of interleukin 6 and CD14 was positively associated with muscle, but not liver, insulin sensitivity. The present findings demonstrate that circulating immune cell populations and inflammatory gene expression in aSAT show distinct associations with liver and muscle insulin sensitivity.

Metabolic surgery-induced changes of the growth hormone system relate to improved adipose tissue function

AimsBody weight loss improves insulin resistance and growth hormone secretion in obesity, which may be regulated by leptin according to preclinical studies. How changes in leptin, lipids and insulin sensitivity after bariatric (metabolic) surgery affect the human growth hormone system is yet unclear.Participants and methodsPeople with obesity (OBE, n = 79, BMI 50.8 ± 6.3 kg/m2) were studied before, 2, 12, 24 and 52 weeks after metabolic surgery and compared to lean healthy humans (control; CON, n = 24, BMI 24.3 ± 3.1 kg/m2). Tissue-specific insulin sensitivity was assessed by hyperinsulinemic-euglycemic clamps with D-[6,6-2H2]glucose. Fasting leptin, growth hormone (GH), insulin-like growth factor 1 (IGF-1) and IGF-binding proteins (IGFBP1, IGFBP3) were measured using ELISA.ResultsAt baseline, OBE exhibited higher glycemia and leptinemia as well as pronounced peripheral, adipose tissue and hepatic insulin resistance compared to CON. GH and IGFBP1 were lower, while IGF1 was comparable between groups. At 52 weeks, OBE had lost 33% body weight and doubled their peripheral insulin sensitivity, which was paralleled by continuous increases in GH, IGF-1 and IGFBP1 as well as decrease in leptin. The rise in GH correlated with reductions in free fatty acids, adipose tissue insulin resistance and insulinemia, but not with changes in body weight, peripheral insulin sensitivity, glycemia or leptinemia. The rise in IGF-1 correlated with reduction in high-sensitive C-reactive protein.ConclusionReversal of alterations of the GH-IGF-1 axis after surgically-induced weight loss is unlikely related to improved leptin secretion and/or insulin sensitivity, but is rather associated with restored adipose tissue function and reduced low-grade inflammation.

Hepatocyte Toll-Like Receptor 4 Mediates Alcohol-Induced Insulin Resistance in Mice.

Accumulating evidence has demonstrated the association between alcohol overconsumption and the development of insulin resistance. However, the underlying mechanisms are not completely understood. To investigate the requirement and sufficiency of hepatocyte toll-like receptor 4 (TLR4) in alcohol-induced insulin resistance, we used two mouse models (Tlr4fl/fl and Tlr4LoxTB) that allow ablation of TLR4 only in hepatocytes (Tlr4LKO) and restoration of endogenous TLR4 expression in hepatocytes on a TLR4-null background (Tlr4LoxTB × Alb-Cre), respectively. A Lieber-DeCarli feeding model was used to induce glucose intolerance and insulin resistance in mice. Glucose tolerance test, insulin tolerance test, and insulin signaling experiments were performed to examine systemic and tissue-specific insulin sensitivity. We found that alcohol-fed hepatocyte TLR4 deficient mice (Tlr4LKO) had lower blood glucose levels in response to intraperitoneal injection of insulin. Moreover, increased phosphorylation of glycogen synthase kinase-3β (GSK3β) was observed in the liver of Tlr4LKO mice after chronic alcohol intake. In contrast, when hepatic TLR4 was reactivated in mice (Tlr4LoxTB × Alb-Cre), alcohol feeding caused glucose intolerance in these mice compared with littermate controls (Tlr4LoxTB). In addition, AKT phosphorylation was dramatically reduced in the liver and epididymal white adipose tissue (eWAT) of alcohol-fed Tlr4LoxTB × Alb-Cre mice, which was similar to that of mice with whole-body TLR4 reactivation (Tlr4LoxTB × Zp3-Cre). Collectively, these findings suggest that hepatocyte TLR4 is both required and sufficient in the development of insulin resistance induced by alcohol overconsumption.

Mitochondrial respiration is decreased in visceral but not subcutaneous adipose tissue in obese individuals with fatty liver disease.

Adipose tissue dysfunction is involved in the development of insulin resistance and is responsible for excessive lipid delivery to other organs such as the liver. We tested the hypothesis that impaired mitochondrial function is a common feature of subcutaneous (SAT) and visceral adipose tissue (VAT), but may differently contribute to adipose tissue insulin resistance (IR) in obesity, non-alcoholic fatty liver (NAFL) and steatohepatitis (NASH). In this cross-sectional study, we analyzed tissue-specific insulin sensitivity using stable isotope dilution and hyperinsulinemic-normoglycemic clamp tests. We also assessed mitochondrial respiration, mRNA and protein expression, and tissue morphology in biopsies of SAT and VAT from obese humans without NAFL, with NAFL or with NASH (n= 22/group). Compared to individuals without liver disease, persons with NAFL and NASH had about 30% (p= 0.010) and 33% (p= 0.002) lower maximal mitochondrial respiration, respectively, in VAT, but not in SAT. The lower maximal mitochondrial respiration of VAT was associated with lower adipose tissue insulin sensitivity (β= 0.985, p= 0.041) and with increased VAT protein expression of tumor necrosis factor A across all groups (β=-0.085, p= 0.040). VAT from individuals with NASH was characterized by lower expression of oxidative phosphorylation complex IV (p= 0.042) and higher mRNA expression of the macrophage marker CD68 (p= 0.002) than VAT from participants without NAFL. Humans with non-alcoholic fatty liver disease have distinct abnormalities of VAT energy metabolism, which correlate with adipose tissue dysfunction and may favor progression of NAFL to NASH. Adipose tissue (commonly called body fat) can be found under the skin (subcutaneous) or around internal organs (visceral). Dysfunction of adipose tissue can cause insulin resistance and lead to excess delivery of fat to other organs such as the liver. Herein, we show that dysfunction specifically in visceral adipose tissue was associated with fatty liver disease. NCT01477957.

Hyperbaric oxygen rapidly improves tissue-specific insulin sensitivity and mitochondrial capacity in humans with type 2 diabetes: a randomised placebo-controlled crossover trial

Aims/hypothesisHyperbaric oxygen (HBO) therapy may improve hyperglycaemia in humans with type 2 diabetes, but underlying mechanisms are unclear. Our objective was to examine the glucometabolic effects of HBO on whole-body glucose disposal in humans with type 2 diabetes.MethodsIn a randomised placebo-controlled crossover trial located at the German Diabetes Center, 12 male individuals with type 2 diabetes (age 18–75 years, BMI <35 kg/m2, HbA1c 42–75 mmol/mol [6–9%]), randomly allocated by one person, underwent 2-h HBO, once with 100% (240 kPa; HBO) and once with 21% oxygen (240 kPa; control, CON). Insulin sensitivity was assessed by hyperinsulinaemic–euglycaemic clamps with d-[6,6-2H2]glucose, hepatic and skeletal muscle energy metabolism were assessed by 1H/31P-magnetic resonance spectroscopy, while high-resolution respirometry measured skeletal muscle and white adipose tissue (WAT) mitochondrial capacity. All participants and people assessing the outcomes were blinded.ResultsHBO decreased fasting blood glucose by 19% and increased whole-body, hepatic and WAT insulin sensitivity about one-third (p<0.05 vs CON). Upon HBO, hepatic γ-ATP concentrations doubled, mitochondrial respiratory control doubled in skeletal muscle and tripled in WAT (p<0.05 vs CON). HBO increased myocellular insulin-stimulated serine-473/threonine-308 phosphorylation of Akt but decreased basal inhibitory serine-1101 phosphorylation of IRS-1 and endoplasmic reticulum stress (p<0.05 vs CON).Conclusions/interpretationHBO-mediated improvement of insulin sensitivity likely results from decreased endoplasmic reticulum stress and increased mitochondrial capacity, possibly leading to low-dose reactive oxygen species-mediated mitohormesis in humans with type 2 diabetes.Trial registrationClinicalTrials.gov NCT04219215FundingGerman Federal Ministry of Health, German Federal Ministry of Education and Research, North-Rhine Westfalia Ministry of Culture and Science, European-Regional-Development-Fund, German-Research-Foundation (DFG), Schmutzler StiftungGraphical abstract

Mild intermittent hypoxia exposure alters gut microbiota composition in men with overweight and obesity.

Results from high altitude studies in humans and controlled animal experiments suggest that hypoxia exposure induces alterations in gut microbiota composition, which may in turn affect host metabolism. However, well-controlled studies investigating the effects of normobaric hypoxia exposure on gut microbiota composition in humans are lacking. The aim of this study was to explore the impact of mild intermittent hypoxia (MIH) exposure on gut microbiota composition in men with overweight and/or obesity. We performed a randomised, single-blind crossover study, in which participants were exposed to MIH (FiO2: 15%, 3×2 h per day) and normoxia (FiO2: 21%) for seven consecutive days. Following the MIH and normoxia exposure regimens, faecal samples were collected for determination of faecal microbiota composition using 16S rRNA gene-amplicon sequencing in the morning of day 8. Paired faecal samples were available for five individuals. Furthermore, tissue-specific insulin sensitivity was determined using the gold-standard two-step hyperinsulinemic-euglycemic clamp. MIH did not affect microbial alpha and beta-diversity but reduced the relative abundance of Christensenellaceae and Clostridiaceae bacterial families. MIH significantly increased the abundances of obligate anaerobic bacterial genera including Fusicatenibacter, Butyricicoccus and Holdemania, whilst reducing Christensenellaceae R-7 group and Clostridium sensu stricto 1, although these findings were not statistically significant after correction for multiple testing. Furthermore, MIH-induced alterations in abundances of several genera were associated with changes in metabolic parameters such as adipose and peripheral insulin sensitivity, plasma levels of insulin, fatty acids, triacylglycerol and lactate, and substrate oxidation. In conclusion, we demonstrate for the first time that MIH exposure induces modest effects on faecal microbiota composition in humans, shifting several bacterial families and genera towards higher abundances of anaerobic butyrate-producing bacteria. Moreover, MIH-induced effects on faecal microbial composition were associated with parameters related to glucose and lipid homeostasis, supporting a link between MIH-induced alterations in faecal microbiota composition and host metabolism. The study was registered at the Netherlands Trial Register: NL7120/NTR7325.

Fecal carriage of vanB antibiotic resistance gene affects adipose tissue function under vancomycin use

ABSTRACT Detrimental consequences of antibiotic treatment may include long-lasting disruption of the gut microbiota. Previous studies found no negative effects of antibiotics on metabolic health, although individualized responses were observed. Here, we aimed to investigate the subject-specific response to vancomycin use in tissue-specific insulin sensitivity by stratifying individuals based on the presence of antibiotic resistance genes (ARGs) or opportunistic pathogens (OPs) in the baseline fecal microbiota. Quantitative Polymerase Chain Reaction (qPCR) was used to detect ARGs and OPs in DNA isolated from fecal samples of 56 males with overweight/obesity (Body Mass Index: 25–35 kg/m2) and impaired glucose metabolism (fasting plasma glucose ≥5.6 mmol/L and/or 2-hour glucose 7.8–11.1 mmol/L). A two-step hyperinsulinemic-euglycemic clamp was performed to determine tissue-specific insulin sensitivity. Abdominal subcutaneous adipose tissue (AT) gene expression was assessed using Affymetrix microarray. Gut microbial composition was determined using the Human Intestinal Tract Chip (HITChip) microarray. At baseline, the vancomycin resistance gene vanB was present in 60% of our population. In individuals that were vanB-negative at baseline, AT insulin sensitivity (insulin-mediated suppression of plasma free fatty acids) improved during vancomycin use, while it decreased among vanB-positive individuals (% change post versus baseline: 14.1 ± 5.6 vs. −6.7 ± 7.5% (p = .042)). The vancomycin-induced increase in AT insulin sensitivity was accompanied by downregulation of inflammatory pathways and enrichment of extracellular matrix remodeling pathways in AT. In the vanB-positive group, well-known vanB-carrying bacteria, Enterococcus and Streptococcus, expanded in the gut microbiome. In conclusion, microbiome composition and adipose tissue biology were differentially affected by vancomycin treatment based on fecal vanB carriage.

1436-P: Metformin Increases Skeletal Muscle Mitochondrial Function and Acute Phase Insulin Sensitivity in Obstructive Sleep Apnea

Introduction: Obstructive sleep apnea (OSA) is a prevalent sleep disorder with high type 2 diabetes (T2D) risk. OSA therapy includes positive airway pressure (PAP) treatment, which resolves breathing events but modestly improves metabolic health. Metformin is recommended for T2D prevention but is not advocated in patients with OSA. Our pilot study evaluated the effects of metformin on glucose metabolism and mitochondrial function in OSA patients. Methods: Sixteen adults (50.5±1.6 years, BMI: 36.4±0.8 kg/m2) with OSA (apnea hypopnea index: 53.2±21.1 events/hour) were randomized to receive placebo (n=8) or metformin (n=8) treatment along with PAP for 3 months in a double-blind parallel-group design. Whole body and adipose tissue-specific insulin sensitivity (IS) was determined by oral glucose tolerance test (OGTT) . Skeletal muscle mitochondrial function was determined by high-resolution respirometry using biopsies obtained at baseline and after 3 months of treatment. Results: Change in whole body IS (Matsuda index) was not different in metformin or placebo treated groups (p=0.46) . However, improved acute phase responses during OGTT - glucose uptake (p=0.02) , insulin release (p=0.03) , and suppressed lipolysis (p=0.03) were observed with metformin treatment relative to control. Increased skeletal muscle mitochondrial function was evident with metformin relative to control. Specifically, metformin increased complex I phosphorylation and complex IV electron transfer capacity. Conclusion: Metformin treatment improves acute phase IS and insulin suppression of lipolysis in OSA patients. Strikingly, metformin improved skeletal muscle mitochondrial function independent of changes in second phase glucose disposal and BMI, indicating improved tissue metabolic function. These data suggest that in patients with OSA, improvement in tissue level metabolic function may precede changes in whole-body IS and metformin may improve metabolism. Disclosure E.R.M.Zunica: None. E.C.Heintz: None. R.C.Hebert: None. M.C.Tanksley: None. E.C.Mader: None. J.P.Kirwan: None. C.L.Axelrod: None. P.Singh: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases (DK123456789) ;National Institute of General Medical Sciences (GM123456789)

Bromodomain Inhibition Reveals FGF15/19 As a Target of Epigenetic Regulation and Metabolic Control.

Epigenetic regulation is an important factor in glucose metabolism, but underlying mechanisms remain largely unknown. Here we investigated epigenetic control of systemic metabolism by bromodomain-containing proteins (Brds), which are transcriptional regulators binding to acetylated histone, in both intestinal cells and mice treated with the bromodomain inhibitor JQ-1. In vivo treatment with JQ-1 resulted in hyperglycemia and severe glucose intolerance. Whole-body or tissue-specific insulin sensitivity was not altered by JQ-1; however, JQ-1 treatment reduced insulin secretion during both in vivo glucose tolerance testing and ex vivo incubation of isolated islets. JQ-1 also inhibited expression of fibroblast growth factor (FGF) 15 in the ileum and decreased FGF receptor 4-related signaling in the liver. These adverse metabolic effects of Brd4 inhibition were fully reversed by in vivo overexpression of FGF19, with normalization of hyperglycemia. At a cellular level, we demonstrate Brd4 binds to the promoter region of FGF19 in human intestinal cells; Brd inhibition by JQ-1 reduces FGF19 promoter binding and downregulates FGF19 expression. Thus, we identify Brd4 as a novel transcriptional regulator of intestinal FGF15/19 in ileum and FGF signaling in the liver and a contributor to the gut-liver axis and systemic glucose metabolism.

Reversible insulin resistance in muscle and fat unrelated to the metabolic syndrome in patients with acromegaly.

SummaryBackgroundPatients with active acromegaly exhibit insulin resistance despite a lean phenotype whereas controlled disease improves insulin sensitivity and increases fat mass. The mechanisms underlying this paradox remain elusive, but growth hormone (GH)-induced lipolysis plays a central role. The aim of the study was to investigative the molecular mechanisms of insulin resistance dissociated from obesity in patients with acromegaly.MethodsIn a prospective study, twenty-one patients with newly diagnosed acromegaly were studied at diagnosis and after disease control obtained by either surgery alone (n=10) or somatostatin analogue (SA) treatment (n=11) with assessment of body composition (DXA scan), whole body and tissue-specific insulin sensitivity and GH and insulin signalling in adipose tissue and skeletal muscle.FindingsDisease control of acromegaly significantly reduced lean body mass (p<0.001) and increased fat mass (p<0.001). At diagnosis, GH signalling (pSTAT5) was constitutively activated in fat and enhanced expression of GH-regulated genes (CISH and IGF-I) were detected in muscle and fat. Insulin sensitivity in skeletal muscle, liver and adipose tissue increased after disease control regardless of treatment modality. This was associated with enhanced insulin signalling in both muscle and fat including downregulation of phosphatase and tensin homolog (PTEN) together with reduced signalling of GH and lipolytic activators in fat.InterpretationIn conclusion, the study support that uncontrolled lipolysis is a major feature of insulin resistance in active acromegaly, and is characterized by upregulation of PTEN and suppression of insulin signalling in both muscle and fat.FundingThis work was supported by a grant from the Independent Research Fund, Denmark (7016-00303A) and from the Alfred Benzon Foundation, Denmark.

Effects of Weight Loss on Adipose and Muscular Neuropilin 1 mRNA Expression in Obesity: Potential Implication in SARS-CoV-2 Infections?

Introduction: Neuropilin 1 (NRP-1) is a novel co-receptor promoting SARS-CoV-2 infectivity. Animal data indicate a role in trans-endothelial lipid transport and storage. As human data are sparse, we aimed to assess the role of NRP-1 in 2 metabolic active tissues in human obesity and in the context of weight loss-induced short- and long-term metabolic changes. Methods: After a standardized 12-week weight reduction program, 143 subjects (age >18; body mass index ≥27 kg/m², 78% female) were randomized to a 12-month lifestyle intervention or a control group using a stratified randomization scheme. This was followed by 6-month follow-up without any intervention. Phenotyping was performed before and after weight loss, after 12-month intervention and after subsequent 6 months of follow-up. Tissue-specific insulin sensitivity was estimated by HOMA-IR (whole body and mostly driven by liver), insulin sensitivity index (ISI)_Clamp (predominantly skeletal muscle), and free fatty acid (FFA) suppression during hyperinsulinemic-euglycemic clamp (FFA_Supp) (predominantly adipose tissue). NRP-1 mRNA expression was measured in subcutaneous adipose tissue (NRP-1_AT) and skeletal muscle (NRP-1_SM) before and after weight loss. Results: NRP-1 was highly expressed in adipose tissue (7,893 [7,303–8,536] counts), but neither NRP-1_AT nor NRP-1_SM were related to estimates of obesity. Higher NRP-1_AT was associated with stronger FFA_Supp (r = −0.343, p = 0.003) and a tendency to higher ISI_Clamp (r = 0.202, p = 0.085). Weight loss induced a decline of NRP-1_AT but not NRP-1_SM. This was more pronounced in subjects with stronger reduction of adipose ACE-2 mRNA expression (r = 0.250; p = 0.032) but was not associated with short- and long-term improvement of FFA_Supp and ISI_Clamp. Conclusion: NRP-1_AT is related to adipose insulin sensitivity in obesity. Weight loss-induced decline of NRP-1_AT seems not to be involved in metabolic short- and long-term improvements after weight loss. However, weight loss-induced reduction of both NRP-1_AT and ACE-2_AT indicates a lower susceptibility of adipose tissue for SARS-CoV-2 after body weight reduction.